CA2177358A1 - Apparatus for reconstructing holographic images - Google Patents

Abstract

An apparatus for reconstructing holographic images includes a white light source, diffraction grating (1112) for generating zero-order diffracted light (1416) and at least first-order diffracted light, and light control film (LCF 1810) which is configured to block the zero-order diffracted light and to facilitate passage of a desired bandwidth of first-order diffracted light therethrough. In one embodiment light control film (LCF 1810) comprises a front layer (1802), a core layer (1804), and a back layer (1806). The back layer (1806) may be thought of as a datum, whereby a lateral shift in front film (1802) results in wavelength selectively, and a corresponding shift in core layer (1804) results in good zero-order light blocking. The resulting light is a pseudo-monochromatic source having sufficient coherence for use as a hologram reconstruction beam.

Description

2 1 7 7 3 ~ ~ PCT/U594/13639 .
Apparatus for Reconstructing 1 I~,luu~phic Imaûes CRQSS-REFERENCE TO RELATED APPLICATIONS
5 This is a continuation-in-part (CIP) of United States Patent Application Serial No. 07/982,3f 6 of the same title filed November 27, 1992 by inventor Stephen J. Hart;
and of International Patent Application No. PCT/US93/11501 of the same title andinventor filed November 26, 1993.
TECHNICAL FIFI n 0 The present invention relates, generally, to methods and apparatus for making holograms, and more particularly to a technique for sequentially exposing a film substrate to a plurality of two-dimensional images ~ tel)ldlive of a three-dimensional physical system to thereby produce a hologram of the physical system.
BAÇKGRQU~ID ART AND TECHNIÇ~I PRQBI F1~5 A hologram is a three-dimensional record, for example a film record, of a physical system which, when replayed, produces a true three-dimensional image of the system.
Holography differs from ~ os-u,uic ,~ ulo~ld,ully in that the holographic image exhibits full parallax by affording an observer a full range of viewpoints of the image from every angle, both horizontal and vertical, and full perspective; i.e., it affords the viewer a full 20 range of perspectives of the image from every distance from near to far. A holographic ~pl~st~ dlion of an image thus provides significant advantages over a stereoscopic l~p~ dlion of the same image. This is particularly true in medical diagnosis, where the examination and understanding of volumetric data is critical to proper medical treatment.
While the examination of data which fills a three-dimensional space occurs in all branches of art, science, and engineering, perhaps the most familiar examples involve medical imaging where, for example, Computerized Axial Tomography (CT or CAT), Magnetic Resonance (MR), and other scanning modalities are used to obtain a plurality of cross-sectional images of a human body part. Radiologists, physicians, and patients 30 observe these two-dimensional data "slices" to discern what the two-dimensional data implies about the three-dimensional organs and tissue I~ d by the data. The integration of a large number of two-dimensional data slices places great strain on the human visual system, even for relatively simple volumetric images. As the organ or tissue WO 9~/14960 ~ 1 7 ~ 3 5 8 PCT/US94/13639 underinvestigationbecomesmorecomplex,theabilitytoproperlyintegratelargeamounts of two-dimensional data to produce meaningful and understandable three-dimensional mental images may become overwhelming.
In prior art holograms employing a small number of superimposed holographic s images on a single film substrate, the existenoe of a relatively small ~e,~:"~d~ of spurious exposed and/or developed photosensitive elements (fog) does not d,l J,I~ idbly degrade the quality of the resulting hologram. In contrast, holograms made in accordance with the subject invention, discussed below, typically employ up to 100 or more hologramssuperimposed on a single film substrate; hence, the presence of a small amount of fog on 0 each hologram would have a serious cumulative effect on the quality of the final product.
A method and apparatus for producing holograms is therefore needed which permits a large number, for example up to several hundred or more different holograms to be recorded on a single film substrate, thereby facilitating the true, three-dimensional holographic reproduction of human body parts and other physical systems which are currently viewed in the form of discrete data slioes.
SUMMARY OF THE INVENTION
The present invention provides methods and apparatus for making holograms which overcome the limitations of the prior art.
In accordance with one aspect of the present invention, a hologram camera 20 assembly comprises a single laser source and a beam splitter configured to split the laser beam into a reference beam and an obied beam and to direct both beams at a film substrate. The assembly further comprises a spatial light modulator configured to sequential ly project a plural ity of two-di mensional i mages, for example a p l ural ity of sl ices of data ~-,""~ i"g a CT scan data set, into the object beam and onto the film. In this 2s man ner, a three-d i mensional holograph ic record of each two-di mensional sl ice of the data set is produoed on the film.
In accordance with another aspect of the invention, the entire data set, consisting of one to two hundred or more individual two-dimensional slices, is su~e, i",~.osed onto the film, resulting in the superposition of one hundred Qr more individual, interrelated 30 holograms on the single substrate (the master hologram~. In contrast to prior art techniques wherein a small number (e.g., one to four) of holograms are superimposed onto a single film substrate, the present invention contemplates methods and apparatus for recording a large number of relatively weak holograms, each consuming an WO 95/14960 ~ ~ ~7 7 ~ 5 ~ PCT/US94113639 d,U,UI U~il, Idlely equal, but in any event proportionate, share of the photosensitive elements within the film.
In accordance with a further aspect of the invention, a reference-to-object copy(transfer) assembly is provided whereby the d~u,~",~lltioned master hologram may be 5 quickly and efficiently reproduced in a single exposure as a single hologram.
In a.-u,-ld"~ with yet a further aspect of the invention, a ho~ogram viewing device is provided for viewing the hologram produced in accordance with the invention.
In particular, an exemplary viewing box in accordance with the present inventioncomprises a suitably enclosed, rectangular apparatus LU~ g a broad spectrum light 0 source, e.g, a white light source mounted therein, a collimating (e.g., Fresnel) lens, a broad spectrum light source, e.&, diffraction grating, and a Venetian blind (louver). The collimating lens is configured to direct a collimated source of white light through the diffraction grating. In the context of the present invention, a collimated light refers to light in which all LU~ JO~ thereof have the same direction of propagation such that 5 the beam has a substantially constant cross-sectional area over a reasonable propagation length.
The diffraction grating is configured to pass light therethrough at an angle which is a function of the wavelength of each light component. The hologram also passes light therethrough at respective angles which are a function of the corresponding wavelengths.
20 By inverting the hologram prior to viewing, all wavelengths of light emerge from the hologram substantially orthogonally thereto BRIEF DES(:RIPTION OF THE DRAWING FIGVRES
The subject invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and Figure 1 shows a typical computerized axial IUIllU~;ld~JIly (CT) device;
Figure 2 shows a plurality of two-dimensional data slices each containing data such as may be obtained by x-ray devices typically employed in the CT
device of Figure 1, the slices cooperating to form a volumetric data set;
Figure 3 shows a schematic diagram of a camera system in d.Lolddl~cl: with a preferred ~ budil~ of the present invention;
Figure 4 shows a schematic diagram of a beam splitter assembly in accordance with a preferred embodiment of the present invention;

WO95/14960 2 ~ 7~ 8 PCT/US94113639 Figure 5A to 5D are graphic illustrations showing the effect of Fourier Llal~ru~ g the laser beam utilized in the camera system of Figure 3;
Figure 6A shows an enlarged schematic diagram of a portion of the camera system of Figure 3;
Figure 6B shows a schematic diagram of an alternative embodiment of the spatial light modulator shown in Figure 3;
Figure 7 shows an enlarged schematic diagram of another portion of the camera system of Figure 3;
Figure 8 shows an enlarged schematic diagram of a portion of the 0 projection assembly utilized in the camera assembly of Figure 3;
Figure 9 shows a schematic layout of an exemplary copy rig in accordance with the present invention;
Figures 1 ûA and 1 ûB set forth orthoscopic and pseudoscopic views, respectively, of a master hologram being replayed in accondance with one aspect of the present invention;
Figure 11 shows a schematic diagram of a hologram viewing apparatus;
Figure 12 is a schematic diagram of an alternative embodiment of a "single step" camera system in accordance with the present invention;
Figure 13 is a schematic diagram of an alternative embodiment of the viewing apparatus shown in Figure 11 in accordance with the present invention;
Figure 14 is a schematic cross-section view of a first alternative embodiment of a laminated, composite light control film (LCF) useful in the context of the viewing apparatus shown in Figure 11;
Figures 15 shows a front view of an exemplary one of the film sheets 2s shown in Figure 14;
Figures 16 and 17 are schematic cross-section views illustrating the effect of manipulating the film sheets of Figure 14 on the passage of first order lightthrough the LCF; and Figure 18 is a schematic cross-section view of a second alternative embodiment of the LCF of Figure 14.
r~ETAlLED DESCRIPTION OF PREFERRED EXE~PLARY EMBODIMENTS
In the context of the present invention, a volumetric data set corresponding to a three-dimensional physical system (e.g., a human body part) is encoded onto a single WO 95/14960 2 1 7 7 3 ~ 8 PCT/US94/13639 recording material, e.g., a pllvlols~d,uhic substrate, to thereby produce a master hologram of the object. The master hologram may be used to produce one or more copies which, when replayed by directing an appropriate light source therethrough, recreates a three-dimensional image of the object exhibiting full parallax and full perspedive. Thus, for 5 a particular data set, the present invention contemplates a plurality of separate, ldled optical systems: a camera system for producing a master hologram; a copy system for generating copies of the master hologram; and a viewing system for replaying either the master hologram or copies thereof, depending on the particular configuration of the camera system.
0 THE DATA SET: -Presently known modalities for generating volumetric data ~ ding to aphysical system include, inter alia, computerized axial lmllo~ld~Jlly (CAT or CT) scans, magnetic resonance scans (MR~, three-dimensional ultra sound (US), positron emission ~nllo~5~dplly (PET), and the like. Although a preferred embodiment of the present 5 invention is described herein in the context of medical imaging systems which are typically used to investigate internal body parts (e.g., the brain, spinal cord, and various other bones and organs), those skilled in the art will appreciate that the present invention may be used in conjunction with any suitable data set defining any three-dimensional distribution of data, regardless of whether the data set represents a physical system, e.g, 20 numerical, graphical, and the like.
Referring now to Figures 1 and 2, a typical CT device comprises a gantry 10 and a table 12, as is known in the art. Table 12 is advantageously configured to move axially (along arrow A in Figure 1) at ,~"~d~l~"~,i"~d increments. A patient (not shown) is placed on table 12 such that the body part to be i,,~..,v~dl~d is generally disposed within the 2s perimeter of gantry 10.
Gantry 10 suitably comprises a pluQlity of x-ray sources and recording devices (both not shown) disposed about its circumference. As the patient is moved axially relative to gantry 10, the x-ray devices record a succession of two-dimensional data slices 14A, 14B, . . . 14X ~,""-,;,i"g the three-dimensional space (volume) 16 containing data 30 obtained with respect to the i~ dl~d body part (see Figure 2). That is, the individual dataslicesl4combinetoformavolumetricdatasetl6which,intotal,comprisesathree-dimensional image of the ill~ dl~d body part. As used herein, the terms "volume" or "volumetric space" refers to volumetric data set 16, including a plurality of two-_5_ WO 95114960 2 1 7 7 ~ 5 ~ PCTI[JS94/13639 dimensional data slices 14, each slice containing particular data regarding the body partu~;d~d by the given modality.
Typical data sets comprise on the order of 10 to 70 (for CT systems) or 12 to 128 (for MR) two- dimensional data slices 14. Those skilled in the art will appreciate that the s thickness and spacing between data slices 14 are configurable and may be adjusted by the CT technician. Typical slice thicknesses range from 1.5 to 10 millimeters and most typically d~ ly 5 millimeters. The thickness of the slices is desirably selected so that only a small degree of overlap exists between each successive data slice.
Presently known CT scan systems generate data slices having a resolution defined0 by, for example, a 256 or a 512 square pixel matrix. Furthermore, each address within the matrix is typically defined by a twelve bit grey level value. Cr scanners are conventionally calibrated in Houndsfield Units whereby air has a density of minus 1,000 and water a density of zero. Thus, each pixel within a data slice may have a grey level value between minus 1,000 and 3,095 (inclusive) in the context of a conventional CT
1s system. Because the human eye is capable of simultaneously perceiving a maximum of approximately one hundred (100) grey levels between pure white and pure black, it is desirable to manipulate the data set such that each data point within a slice exhibits one (1) of d~J,ul~)~dllld~ly fifty (50) to one hundred ~100) grey level values (as opposed to the 4,096 available grey level values). The process of redefining these grey level values is 20 variously referred to as "windov.~ing" (in radiology); "stretching" (in remote sensing/satellite imaging); and "photometric correction" (in astronomy).
The present inventor has d~l~llllillt:d that optimum contrast may be obtained bywindowing each data slice in accordance with its content. For example, in a CT data slice which depicts a cross-section of a bone, the bone being the subject of examination, 2s the relevant data will typically exhibit grey level values in the range of minus 600 to 1,400. Since the regions of the data slice exhibiting grey level values less than minus 600 or greater than 1,400 are not relevant to the examination, it may be desirable to clamp all grey level values above 1,400 to a high value corresponding to pure white, and those data points having grey level values lower than minus 600 to a low value corresponding 30 to pure black.
As a further example, normal grey level values for brain matter are typically in the range of about 40 while grey level values ~"t:~,uonding to tumorous tissue may be in the 120 range. If these values were expressed within a range of 4,096 grey level values, it WO 95114960 2 1 ~ 7 ~ 5 8 PCI/US94/13639 .
would be extremely difficult for the human eye to distinguish between normal brain and tumorous tissue. Therefore, it may be desirable to clamp all data points having grey level values greater than, e.g., 140, to a very high level ~nlt:a,uOI)d;llg to pure white, and to clamp those data points having grey scale values of less than, e.g., minus 30, to a very s low value corresponding to pure black. Windowing the data set in this manner contributes to the production of sharp, unambiguous holograms.
In addition to windowing a data set on a slice-to-slice basis, it may also be advantageous, under certain circumstances, to perform differential windowing within a particular slice, i.e., from pixel to pixel. For example, a certain slice or series of slices 0 may depict a deep tumor in a brain, which tumor is to be treated with radiation therapy, for example by irradiating the tumor with one or more radiation beams. In regions which are not to be irradiated, the slice may be windowed in a relatively dark manner. In regions which will have low to mid levels of radiation, a slice may be windowed somewhat more brightly. In regions of a high ~u~ dlion of radiation, the slioe may 5 be windowed even brighter. Finally, in regions actually containing the tumor, the slice may be windowed the brightest. In the context of the present invention, the resulting hologram produces a ghostly image of the entire head, a brighter brain region, with the brightest regions being those regions which are either being irradiated (if the data set was taken during treatment) or which are to be irradiated.
A further preprocessing technique useful in the context of the present inventionsurrounds manipulating the aggregate brightness level for some or all of the slices within a particular data set to thereby reduce the differences in aggregate brightness level from slice to slice and to reduce the need for long exposure times for same or all of the slices.
This technique is sometimes referred to herein as adding "asteroids" to certain data slices 25 to enhance their brightness level.
More particularly and as discussed below in greater detail, each slice ~olllp~ gthe finished hologram desirably consumes its proportionate share of available photo-sensitive elements within the holographic substrate during processing of the hologram.
In accordance with one aspect of the invention, this is achieved by coordinating various 30 processing ~dldlll~la for each data slice including, for example, the beam ratio, the aggregate brightness level for the particular data slice and the exposure time during which the particular data slice is projected on to the film substrate. As a general principle, brigh~r d~ta slices requi ~ Iess exposure tim~ and relatively faint data slices require a higher exposure time. in order to reduce the exposure time for faint slices, the aggregate brightness level for a particular faint slice may be artificially boosted by adding a random or otherwise irregular pattern of bright spots to the data slice, preferably in the wings of the data slice remote from the image under examination. Alternatively, the portion of the 5 object beam laser light may be diverted prior to passing through the data slice, for example through the use of an additional beam splitter, and controllably projected onto the film service. If desired, the diverted beam may be passed through as variable intensity polarizer, which polarizer comprises a random pattern of white spots, the intensity of which may be modulated to achieve a desired "astroid" beam intensity. In this regard, 0 the asteroid may ~u~p~u~;se a small pattern of bright spots, a large pattern of relatively diffused spots, or a ~ur~ dlioll of both. In accordance with a further aspect of the invention, the aforementioned polarizer may comprise a polaroid disk configured with asteroids, which disk may be rotated to modulate the asteroid intensity. Further, the asteroid disk may be equipped with a shutter to effectively shunt the asteroid beam for 5 those slices which do not require an artificially elevated aggregate brightness level. This pattern of random white spots, or asteroids, artificially enhances the aggregate gray scale value of the slice, thereby reducing the exposure time for the slice. If desired, the asteroids may be subsequently masked from view in the final, finished composite hologram.
Another step in preparing the data set involves cropping, whereby regions of each data slice or even an entire data slice not germane to the examination are simply eliminated. Cropping of unnecessary data also contributes to the formation of sharp, unambiguous holograms.
~lore particularly, each point within the volume of the emulsion exhibits a 25 microscopic fringe pattern ~u~ JUll~;lillg to the entire holographic image from a unique viewpoint. Stated another way, an arbitrary point at the lower left hand corner of a holographic film comprises an interference fringe pattern which encodes the entire holographic image as the image is seen from that particular point. Another arbitrary point on the holographic film near the center of the film will comprise an interference fringe 30 pattern ,~,u,~st:"~dlive of the entire holographic image when the image is viewed from the oenter of the film. These same phenomenon holds true for every point on the hologram.
As briefly discussed above, a suitable ,ullù~o~;,dul~ic substrate preferably comprises a volume of photographic emulsion which adheres to the surface of a plastic substrate, for WO95/14960 i~ ~ 7j'~5~ PCI/US94/13639 example triacetate. The emulsion typically comprises a very large number of silver halide crystals (grains) suspended in a gelatinous emulsion. Inasmuch as the emulsion contains a finite quantity of crystals, the elimination of u"l1e~ , y data (cropping) within a data slice ensures that substantially all of the silver halide grains which are converted (exposed) 5 for each data slice ~u~uol~d the relevant data from each slice. By conserving the number of silver halide grains which are converted for each data slice, a greater number of slices may be recorded onto a particular piece of film.
THE CAMERA SYSTEM
Once a data set is properly prepared (e.g., windowed and cropped), an individual10 hologram of each respective data slice is su,ue,i",,uos~d onto a single film substrate to generate a master hologram. In accordance with a preferred embodiment, each individual hologram corresponding to a particular data slice is produced while the data ~u"~uoi,di"g to a particular slice is disposed at a different distance from the film substrate, as discussed in greater detail below.
Referring now to Figures 3-4, a camera system 3û0 in accordance with the presentinvention suitably comprises a laser light source 302, a shutter 306, a first mirror 308, a beam splitting assembly 310, a second mirror 312, a reference beam expander 314, a collimatinglens316,afilmholder318,athirdmirror320,anobjectbeamexpander322, an imaging assembly 328, a projection optics assembly 324, a rear projection screen 20 comprising a diffusing surface 472 having a polarizer 327 mounted thereto, and a track assembly 334. Imaging assembly 328, projection optics assembly 324, and rear projection screen 326 are suitably rigidly mounted to track assembly 334 so that they move in unison as track assembly 334 is moved axially along the line indicated by arrow F. As discussed in greater detail below, track assembly 334 is advantageously configured 2s to replicate the relative positions of data slices ~u"".ii~i"g the subject of the hologram.
In a preferred embodiment, total travel of track assembly 334 is suitably sufficient to accommodatetheactualtraveloftheparticularscanningmodalityemployedingenerating the data set, for example on the order of 6 inches.
Camera assembly 300 is illustratively mounted on a rigid table 304 which is 30 suitably insulated from environmental vibrations. Laser source 302 suitably comprises a conventional laser beam generator, for example an Argon ion laser including an etalon to reduce the bandwidth of the emitted light, preferably an innova 306-SF manufactured by Coherent, Inc. of Palo Alto, California. Those skilled in the art will appreciate that _9, WO95/14960 2 1 773~ PCT/US94/13639 laser 302 suitably generates a monochromatic beam having a wavelength in the range of 400 to 750 I~dllOIll~l~ (nm), and preferably about 514.5 or 532 nm. Those skilled in the art will appreciate, however, that any suitable wavelength may be used for which the selected,ul,u~uE;,d,ul~icmaterialis~u",,~,dliL,le,includingwavelengthsintheultravioletand 5 infrared ranges.
Alternatively, laser 302 may comprise a solid state, diode-pumped frequency-doubled YAG laser, which suitably emits laser light at a wavelength of 532 nm. These lasers are capable of emitting in the range of 300 to 600 million watts of pure light, are extremely efficient and air-cooled, and exhibit high stability.
Laser 302 should also exhibit a coherence length which is at least as great as the difference between the total path traveled by the reference and object beams, and preferably a coherence length of at least twice this difference. In the illustrated embodiment, the nominal design path length traveled by the reference beam is equal to that of the object brain (d~plu~illldl~ly 292 centimeters); however, due to, inter alia, the 15 geometry of the setup, the particular reference angle employed, and the size of the film, some components of the reference and object beams may travel a slightly greater or lessor path length. Hence, laser 302 suitably exhibits a coherence length in excess of this difference, namely, c~ uxi~dlely two (2) meters.
Shutter 306 suitably comprises a conventional r~ u",e~l,d"ical shutter, for 20 example a Uniblit~ 35 model no. Lr~54Z manufactured by Vincent Associates of Rochester, New York. In a preferred embodiment, shutter 306 may be remotely actuated so that a reference beam and an object beam are produced only during exposure of the film substrate, effectively shunting the laser light from the system (e.g., via shutter 306~
at all other times. Those skilled in the art will appreciate that the use of a shutter is 25 u~",e~ d~y if a pulse laser source is employed. Moreover, it may be desirable to incorporate a plurality of shutters, for example a shutter to selectively control the reference beam and a different shutter to separately control the object beam, to permit independent control of each beam, for example to permit independent measurement and/or calibration of the respective intensities of the reference and object beams at the 30 film surface.
The various mirrors (e.g., first mirror 3û8, second mirror 312, third mirror 320, etc.) employed in camera assembly 300 suitably comprise conventional front surface mirrors, for example a dielectric mirror coated on a pyrex substrate, for example stock WO 95/14960 2 1 7 7 3 ~ 8 PCT/US94113639 mirror 10D20BD.1, manufactured by Newport. For a typical laser having a beam diameter on the order of 1.5 millimeters, mirror 308 suitably has a surface of d~Jplo~ ly 1 inch in diameter.
First mirror 308 is suitably configured to direct a source beam 402 to beam splitting assembly 310. In the illustrated t:,llL,o.li",~"~, first mirror 308 changes the direction of beam 402 by 90 degrees. Those skilled in the art, however, will appreciate that the relative disposition of the various optical components ~U~pli~illg camera assembly 300, and the particular path traveled by the various beams, are in large measure a function of the physical size of the available components. As a working premise, it is 0 desirable that the reference beam and object beam emanate from the same laser source to ensure proper ~u"~ld~iu" between the reference and the object beam at the surface of film holder 318, and that the path traveled by the reference beam from beam splitter 310 to film 319 is dp!,lu,.il"dlt:ly equal to the path traveled by the object beam from beam splitter 310 to film 319.
With momentary reference to Figure 4, beam splitter assembly 310 preferably comprises a variable wave plate 404, respective fixed wave plates 408 and 412, respective beam splitting cubes 406 and 414, and a mirror 416. On a gross level, beam splitting assembly 310 functions to separate source beam 402 into an object beam 410 and a reference beam 418. Moreover, again with reference to Figure 3, beam splitter assembly 310 also cooperates with imaging assembly 328 and polarizer 327 to ensure that the reference beam and the object beam are both purely polarized in the same polarization state, ;.e., either substantially S or P polarized as discussed in greater detail below, when they contact an exemplary film substrate 319 mounted in film holder 318.
By ensuring that the reference and object beams are pure polarized in the same 25 polarization state, sharp, low noise i"l~,r~ ".~ fringe patterns may be formed.
With continued reference to Figure 4, beam 402 generated by laser source 302 enters beam splitting assembly 310 in a relatively pure polarization state, for example as S polarized light. In the context of the present invention, S polarized light refers to light which is polarized with its electric field oscillating in a vertical plane; P polarized light 30 refers to light having its electric field oriented in a horizontal plane. Beam 4û2 then passes through variable wave plate 404 whereupon the beam is converted into a beam 403, convenientlydefinedas-~ risillgamixtureofSand Ppolarized lightcomponents.
Beam 403 then enters beam splitting cube 406, which is suitably configured to split beam WO gS/14960 2 1 7 ~ 3 5 8 I'CTIUS94113639 403 into a first beam 405 ~u~ n i~ g the P polarized light ~ulll,uol~l ll of beam 403 and a second beam 407 ~u"~u~ illg the 5 polarized light .u"IpUIl~lll of the beam 403. Beam splitting cube 406 suitably comprises a broad band beam splitter, for example a broad band polarization beam splitter, part no. 05FC1 6PB.3, manufactured by Newport.
5 Although beam splitting cube 406 is ideally configured to pass all of (and only) the P
polarized component of beam 403 and to divert all of (and only) the S polarized ~ur~Ju~ ll of 403, it has been observed that such cubes are generally imperfect beam splitters, ignoring small losses due to reflection off of beam splitter surfaces. More precisely, such cubes typically exhibit an extinction ratio on the order of a thousand to 0 one such that approximately 99.9 percent of the S polarized component of beam 403 is diverted into beam 407, and such that dp~lu7~illldl~ly 9û percent of the P polarized component of beam 403 passes through cube 406. Thus, beam 407 comprises 99.9 percent of the S polarized ~ulll,uo~ of beam 403, and approximately 10 percent of the P polarized component of beam 403; similarly, beam 405 comprises d,uplu~dllldlt:ly 90 s percent of the P polarized ~u~ elll of beam 403 and dpplu~dllldl~ly 0.1 percent of the S polarized cûmpûnent of beam 403.
Wave plates 404, 408, and 412 suitably comprise half wave plates for the laser wavelength in use, e.g, part no. 05RP02 manufactured by Newport. Wave plate 404 is configured to convert the S polarized beam 402 into a pl~d~ ed ratio of S and P
20 polarized u",~ "ls. In a preferred embodiment, variable wave plate 404 comprises an LCD layer, which layer changes the polarization of the incoming beam in accordance with the voltage level at the LCD layer. A suitable wave plate 404 may comprise a Liquid Crystal Light Control System, 932-VIS available from Newport. Accordingly, wave plate 404 divides S polarized beam 402 into a mixture of S and P polarized light as a function 25 of applied voltage. By manipulating the voltage on wave plate 404, the operator thereby controls the ratio of the intensity of the reference beam to the intensity of the object beam (the beam ratio). In a preferred embodiment, this ratio as measured at the plane of film 319 is approximately equal to unity.
In any event, beam 405 is almost completely pure P polarized, regardless of the 30 voltage applied to wave plate 4û4; beam 407 is ideally pure S polarized, but may nonetheless contain a substantial P polarized component, depending on the voltage applied to wave plate 404.

WO95114960 2 1 7 7 3 ~ ~ PCT/US94/13639 With continued reference to Figure 4, beam 4û5 then travels through wave plate 408 to convert the pure P polarized beam 4û5 to a pure S polarized object beam 41û.
Beam 407 is passed through wave plate 412 to convert the substantially S polarized beam toasubstantiallyPpolarizedbeam4û9whichthereafterpassesthroughsplittingcube414 5 to eliminate any extraneous S ~u~po~ . In particular, 99.9 percent of the residual S
un~uol~llL of beam 409 is diverted from cube 414 as beam 415 and shunted from the system. In the context of the present invention, any beam which is shunted from, or otherwise removed from the system may be conveniently employed to monitor the intensity and quality of the beam.
0 The p,~dD",in.l"tly P ~ur~,uul~ of beam 409 is passed through cube 414 and reflected by respective mirrors 416 and 312, resulting in a substantially pure P polarized reference beam 418. As discussed in greater detail below, by dividing source beam 402 into object beam 410 and reference beam 418 in the foregoing manner, both the object beam and reference beam exhibit extremely pure polarization, for example on the order 5 of one part impurity in several thousand. Moreover, a high degree of polarization purity is obtained regardless of the beam ratio, which is conveniently and precisely controlled by controlling the voltage applied to variable wave plate 404.
With continued reference to Figures 3 and 4, beam 418 is reflected off mirror 312 and enters beam expander 314. Beam expander 314 preferably comprises a conventional 20 positive lens 421 and a tiny aperture 420. The diameter of beam 418 at the time it enters beam expander 314 is suitably on the order of approximately 1.5 millimeters (essentially the same diameter as when it was ~ l,a,~5ed from laser 302). Positive lens 421 is configured to bring beam 418 to as small a focus as practicable. A suitable positive lens may comprise ",'~,us~upe objective M-20X manufactured by Newport. Aperture 420 2s suitably comprises a pin-hole aperture, for example a PH-15 aperture manufactured by Newport. For good quality lasers which emit pure light in the fundamental transverse rullld~ lic mode (TEMoo), a good quality lens, such as lens 421, can typically focus beam418downtotheorderofdl.p,uxi,,,dlely10to15micronsindiameter. Atthepoint of focus, the beam is then passed through aperture 420, which suitably comprises a small 30 pin hole on the order of 15 microns in diameter. Focusing the beam in this manner effects a Fourier transform of the beam.
More particularly and with reference to Figures 5A-5D, the TEMoo mode of propagation typically exhibited by a small diameter laser beam follows a Gaussian WO95/14960 2 ~ 7~ 3 5 8 PCTNS94/13639 distribution transverse to the direction of propagation of the beam. With specific reference to Figure 5A, this means that the intensity (I) of beam 418 exhibits a Gaussian distribution over a cross-section of the beam. For a Gaussian beam having a nominal diameter of one millimeter, a small amount of the beam at very low intensity extends 5 beyond the one millimeter range.
With reference to Figure 5B, a more accurate ~,ul~sellLdlion of the ideal condition shown in Figure 5A illustrates a substantially Gaussian distribution, but also including the random high frequency noise inevitably imparted to a beam as it is bounced off mirrors, polarized, etc. Note that Figure 5B exhibits the same basic Gaussian profile of the 10 theoretical Gaussian distribution of Figure 5A, but further including random high frequency noise in the beam form ripples.
It is known that the Fourier transform of a Gaussian with noise produces the same basic Gaussian profile, but with the high frequency noise ~u",,uo"~"I~ shifted out onto the wings, as shown in Figure 5C. When the Fourier transform of the beam is passed through an aperture, such as aperture 420 of beam expander 314, the high frequency wings are clipped, resulting in the extremely clean, noise free Gaussian distribution of Figure 5D.
Quite literally, focusing the beam to dp~lJIUXillldl~ a point source, and thereafter passing it through an apenure has the effect of shifting the high frequency noise to the outer bounds of the beam and clipping the noise.
Beam expander 314 thus produces a substantially noise free, Gaussian distributeddivergent reference beam 423.
In a preferred embodiment of the present invention, lens 421 and aperture 420 suitably comprise a single, integral optical ~UIllUUllt:llt, for example a Spatial Filter model 900 manufactured by Newport. Beam expander assembly 314 advantageously includes a screw thread, such that the distance between lens 421 and aperture 420 may be precisely controlled, for example on the order of about 5 millimeters, and two onhogonal set screws to control the horizontal and vertical positions of the aperture relative to the focus of lens 421.
With continued reference to Figure 3, mirror 312 is suitably configured to direct beam 423 at film 319 at a ~u~L~",i"ed angle which closely dpplu~dllldI~ Brewster's angle for the material ~UII~UIi~illg film 319. Those skilled in the an will appreciate that Brewster's angle is often defined as the arc tangent of the refractive index of the material upon which the beam is incident (here, film 319~. Typical refractive indices for such films WO 95/1~96~ 2 1 7 ~ 3 5 8 PCT/IJS94113639 .
are in the range of au,u,u~i,,,dlely 1-5 plus or minus 0.1. Thus, in aordance with a preferred ~",bodi",~"t of the invention, mirror 312 is configured such that beam 423 strikes film 319 at a Brewster's angle of a~uu,uxi,,,dl~ly 56 degrees (arc tan 1.5 - 56 degrees). Those skilled in the art will also appreciate that a P polarized beam incident 5 upon a surface at Brewster's angle will exhibit minimum reflection from that surface, resulting in maximum refraction of reference beam 423 into film 319, thereby facilitating maximum interference with the object beam and minimum back reflected light whichcould otherwise eventually find its way into the film from an incorrect diredion.
Referring now to Figures 4 and 6-7, object beam 410 is reflected by mirror 320 0 and directed into beam expander 322 which is similar in structure and function to beam expander 314 described above in conjunction with Figure 4. A substantially noise free, Gaussian distributed divergent object beam 411 emerges from beam expander 322 and is collimated by a collimating lens 434, resulting in a collimated object beam 436 having a diameter in the range of approximately 5 ~:"ti"~t:le~s. Collimating lens 434 suitably 5 comprises a bi-convex opticai glass lens KBX148 manufadured by Newpûrt. Collimated object beam 436 is applied to imaging assembly 328.
With reference to Figures 7 and 8, imaging assembly 328 suitably comprises a cathode ray tube (CRT) 444, a light valve 442, a wave plate 463, and a polarizing beam splitting cube 438. In a preferred embodiment, beam spl itting cube 438 is dl~pl UXill IdLt~ly 20 a 5 centimeter square (2 inch square) cube. As discussed in greater detail below, a beam 460, ~u~ul i,il,g a P polarized beam which incorporates the data from a data slice through the action of imaging assembly 328, emerges from imaging assembly 328 and is applied to projection optics assembly 324.
As discussed above, a data set ~u~ll,u~ lg a plurality of two-dimensional images25 corresponding to the three~i",~"siu"al subject of the hologram is prepared for use in producing the master hologram. The data set may also be maintained in an electronic data file in a conventional multi-purpose computer (not shown). The computer interfaces with CRT 444 such that the data slices are lldll~llliLI~d, one after the other, within imaging assembly 328.
More particularly, a first data slice is projected by CRT 444 onto light valve 442.
As explained in greater detail belûw, the image corresponding to the data slice is applied to film 319. The reference and object beams are applied to film 319 for a pr~d~Lt:"" ,e i amount of time sufficient to permit film 319 to capture (record) a fringe pattern associated WO 95/14960 2 ~ 7 7 3 5 8 PCTIU594113639 with that data slice and thereby create a hologram of the data slice within the emulsion ~ulllu~ lg film 319. Thereafter, track assembly 334 is moved axially and a subsequent data slice is projected onto fil m 319 in accordance with the distances between data sl ices;
a subsequent hologram ~u~ ol~ding to the subsequent data slice is thus s~,uel illluosed 5 onto film 319. This process is sequentially repeated for each data slice until the number of holograms superimposed onto film 319 ~ur~,uoll~ to the number of data slices 14 ~u~,uli~illg the particular volumetric data set 16 which is the subjed matter of the master hologram being produced.
More particularly and with continued reference to Figures 7 and 8, CRT 444 0 suitably comprises a conYentional fiber-optic face-plate CRT, for example, 41397T1 manufactured by the Hughes Aircraft Company of Carlsbad, California. CRT 444 is configured to project an image corresponding to a particular data slice onto the left hand side of light valve 442 (Figure 7).
In a preferred embodiment, light valve 442 is a Liquid Crystal Light Valve H416015 manufactured by Hughes Aircraft Company of Carlsbad, California. With specific reference to Figure 8, light valve 442 preferably comprises a photocathode 454, a mirror 450, having its mirrored surface facing to the right in Figure 8, and a liquid crystal layer 452. Liquid crystal layer 452 comprises a thin, planar volume of liquid crystal which alters the polarization of the light passing therethrough as a fundion of the localized 20 voltage level of the liquid crystal.
Photocathode 454 comprises a thin, planar volume of a photovoltaic material which exhibits localized voltage levels as a function of light incident thereon. As the image corresponding to a particular data slice 14 is applied by CRT 444 onto photocathode 454, local photovoltaic potentials are formed on the surface of 2~ photocathode 454 in direct correspondence to the light distribution within the cross-section of the applied image beam. In particular, the beam generated by CRT 444 ~u~ ,uùl)di~g to the data slice typically comprises light regions corresponding to bone, soft tissue, and the like, on a dark background. The dark background areas predictably exhibit relatively low grey scale values, whereas the lighter regions of the data slice 30 exhibit correspondingly higher grey scale values. A charge distribution corresponding to the projected image is produced on the surface of photocathode 454.
The static, non-uniform charge distribution on photocathode 454, corresponding to local brightness variations in the data embodied in a particular data slice 14, passes WO 95/14960 2 1 7 7 3 ~ ~ PCT/[JS94/13639 through mirror450 and produces ~u~ ùl~dil lg localized voltage levels across the surface of liquid crystal layer 452. These localized voltage levels within liquid crystal layer 452 rotate the local liquid crystal in plùpulliu~- to the local voltage level, thereby altering the pure S polarized light diverted from cube 438 onto mirrored surface 450, into localized 5 regions of polarized light having a P ~u~po~ associated therewith, as the light passes through crystal layer 452 and is reflected by mirror 450. The emeging beam 460 exhibits (in cross-section) a distribution of P polarized light in accordance with the voltage distribution within crystal layer 452 and, hence, in accordance with the image corresponding to the then current data slice 14.
0 Substantially all (e.g., 99.9%) of the S polarized light ~ulll~JIisillg beam 436 is diverted by cube 438 onto liquid crystal layer 452. This S polarized light is converted to P polarized light by liquid crystal layer 452 in accordance with the voltage distribution on its surface, as described above. The P polarized light is reflected by the mirrored surface of mirror 450 back into cube 438; the P polarized light passes readily through cube 438 into projection optics assembly 324.
The S ~c""po"e,~l of the beam reflected off of the mirrored surface of mirror 450 will be diverted 90 degrees by beam splitting cube 438. To prevent this stray S polarized light from re-entering the system, cube 438 may be tilted slightly so that this S polarized light is effectively shunted from the system.
The resultant beam 460 exhibits a distribution of P polarized light across its cross-section which directly corresponds to the data embodied in the data slice currently projected by CRT 444 onto light valve 442. As a result of the high extinction ratio of cube 438, beam 460 comprises essentially zero S polarization. Note also that the small portionofSpolarizedlight~u",~,~i,i"gbeam436which isnotreflectedbycube438into light valve 442 (namely, a beam 440) may be conveniently shunted from the system.
Beam splitting cube 438 is similar in structure and function to beam splitting cubes 406 and 414, described herein in connection with Figure 4, and preferably comprises a large broad band polarization beam splitter, for example a PBS-514.5-200 manufactured by CVI Laser Corporate of Albuquerque, New Mexico. In a preferred embodiment, beam splitting cube 438 has a cross-section at least as large as the image projected by CRT 444 onto light valve 442, e.g., 2 inches. This is in contrast to beam splitting cubes 406 and 414whichcanadvantageouslybeofsmallercross-section,e.g.,one-halfinch,~u""ud~c,Lle to the diameter of the unexpanded beam 402 from laser 302.
-17~

In the context of the present invention, light which is variously described as removed, eliminated, or shunted from the system may be disposed of in any number of convenient ways. For example, the light may be directed into a black box or onto a black, preferably textured surface. The precise manner in which the light is shunted, or s the particular location to which the light is shunted is largely a matter of convenience;
what is important is that light which is to be removed from the system be prevented from striking the film surface of a hologram (for reasons discussed herein), and further that the light be prevented from reentering the laser source which could disturb or even damage the laser.
0 Althoughprojectionoptics328illustrativelycompriseslightvalve442,anysuitablemechanism which effectively integrates the image ~u~,uo~ lg to a data slice into the object beam will work equally well in the context of the present invention. Indeed, light beam 460, after emerging from cube 438, merely comprises a nonuniform distribution of P polarized light which varies in intensity according to the distribution of data on the then 5 current data slice 14. The cross-section of beam 46û is substantially identical to a hypothetical beam of P polarized light passed through a ul,ulu~,d,ul~ic slide of the instant data sl ice.
Moreover, any suitable ",~.I,d~ l" may be employed in addition to or in lieu of CRT 444 to project data onto light valve 442. For example, a reflective, transmissive or 20 transflective LCD may be employed, which panel may be selectively energized on a pixel-by-pixel basis to thereby replicate the data corresponding to each particular data slice.
Alternatively, an dupluplidLe beam, for example a laser beam, may be suitably Id~ dlllled across the rear surfaoe of light valve 442 to thereby replicate the data corresponding to each data slice.
2s In yet a further embodiment, although CRT 444 is shown in Figure 7 as abutting light valve 442, it may be desirable to configure the projection assembly such that CRT
444 is separated from light valve 442. Such a separation may be desirable, for example, if the diameter of CRT 444 is larger than the diameter of light valve 442 such that the image projected by CRT 444 is desirably projected onto the rear surface of light valve 30 442, for example, through the use of an dpu~u,ulidl~ lens disposed therebetween.
Moreover, it may also be desirable to employ a fiber optic coupling between light valve 442 and CRT 444, regardless of whether an intervening lens is employed, and further regardless of the magnitude of the separation therebetween.

WO95/14960 2 ~ 77~S~ PCT/US94/13639 Moreover, projection optics 328 may be wholly replaced by a suitable spatial light modulator (SLM; not shown) conveniently mounted in the object beam path. In this way, the laser light ~u~,u~ lg the object beam would pass through the SLM, with the SLM
imparting to the object beam information corresponding to a particular image. Depending - 5 on the type of SLM used, such an dl I dl l~ may be employed either with or without the use of a diffuser between the SLM and film holder 319, as appropriate.
With continued reference to Figures 7 and 8, wave plate 463 is suitably interposed between light valve 442 and beam splitting cube 438. Wave plate 463 functions tocorrect certain undesirable polarization which light valve 442 inherently produces.
0 More particularly, light valve 442 polarizes the light which passes through liquid crystal layer 452 in accordance with the local voltage distribution therewithin.Specifically, the applied voltage causes the liquid crystals to rotate, e.g, in an elliptical manner, the amount of rotation being proportional to the localized voltage level. That is, a very high voltage produces a large amount of liquid crystal rotation, resulting in a 5 high degree of altercation of the polarization of the light passing through the rotated crystals. On the other hand, a very low voltage produces a correspondingly small degree of liquid crystal rotation, resulting in a ~or,~uol~di"gly small amount of altercation in the level of polarization. However, it has been observed that a very small degree of liquid crystal rotation (pre-tilt) exists even in the absence of an applied voltage. Thus, 20 d~Jplu,~i",dI~lyonepercentoftheSpolarizedlightpassingthroughliquidcrystallayer452 is converted to P polarized light, even within local regions of liquid crystal layer 452 where no voltage is applied. While this very small degree of spurious polarization does not generally degrade the p~,~u""a".~ of light valve 442 in most contexts, it can be p~ublenldLic in the context of the present invention. For example, if one percent of pure 2~ S polarized light is inadvertently converted to P polarized light, the contrast ratio of the resulting hologram may be substantially limited.
Wave plate 463 is configured to ~o" ,,u~, ISdl~ for the foregoing residual polarization by, for example, imparting a ~,~d~ "" ,ed polarization to the light passing therethrough, which is calculated to exactly cancel that amount of polarization induced by liquid crystal 30 layer 452 in the absence of an applied voltage. By eliminating this undesiredpolarization, the effective contrast ratio of the resulting hologram is limited only by the degree of control achieved in the various process Udldlll~ , as well as the inherent capabilities of the equipment ~UIIIpli~illg camera assembly 300.
_19_ W095114960 ~ 7 77~ PCTIUS94113639 of the SLM output beam will be subsequently disrupted and repolarized in any event.
Referring now to Figure 6B, an alternative embodiment of the camera assembly shown in Figure 6A will now be described. In particular, incoming beam 410 is passed through beam expander 322 and collimating lens 434. Collimated beam 436 is then 5 passed through a liquid crystal display (LCD) SLM 1302, whereupon the image w"t~i onJ;"g to a data slice is interposed into the collimated beam.
In accordance with the alternate embodiment set forth in Figure 6B, LCD 1302 suitably comprises a transmissive, pixelated LCD, for example, a 640 by 480 pixel screen.
Inasmuch as transmissive LCD 1302 will typically impart a "pretilt" to the light passed 0 through it, it may also be desirable to pass incoming beam 410 through a wave plate 1308 to ~,",i e~ for the pretilt.
The output from LCD 13û2 comprises a collimated object beam having local variations in the degree of polarization corresponding to the data embodied in the particular data slice displayed by LCD 1302. As such, it is necessary to convert the 15 variations in polarization within the beam may be conveniently converted into variations in intensity, for example, through the use of a suitable output polarizer (transducer) 1304.
Because high quality polarizers tend to be quite expensive, the polarization/intensity conversion may be suitably effected through the use of a smaller transducer 1306interposed within the object beam downstream of projection lens 462 (where the beam 20 has a smaller cross-section).
Commercially available liquid crystal display (LCD) SLM's are typically designedfor use with unpolarized light. Hence, conventional SLM's generally include an input polarizer such that unpolarized input light is converted to a desired polarization state before being modulated within the SLM. In addition, ~,"""~,~ially available SLM's 2s typically rotate the polarization at each pixel and include an output polarizer (transducer) configured to convert variations in polarization into corresponding variations in intensity.
Inasmuch as high-quality polarizers tend to absorb light and are typically quite expensive, it may be advantageous to employ an SLM in the context of the present invention which does not include one or both of an input polarizer and an output polarizer indeed, the 30 light entering the SLM in accordance with the preferred embodiments discussed herein will be typically purely polarized in any event, thus rendering a separate input polarizer for the SLM unneoessary. Moreover, the output of the SLM in the context of the preferred embodiments discussed herein will often be manipulated, e.g., by applying it to a WO 95/14960 2 1 7 7 3 5 8 PCI`IUS94/13639 .
diffusing screen or the like which may disrupt the polarization state of the output beam, whereupon the disrupted beam may be subsequently repolarized, as desired. That being the case, it is unnecessary to pass the beam as it ieaves the SLM through a polarizer inasmuch as the polarization state of the SLM output beam will be subsequently disrupted s and repolarized in any event.
By eliminating one or both of the input and output polarizer in the SLM, two levels of efficiency may be achieved:
(1) laser light is conserved to the extent u~ e~Sdly absorption of light in the input/output polarizer is eliminated; and (2) eliminating ~ dly hardware components reduces the cost of the assembly.
With reference to Figures 6 and 7, projection optics assembly 324 suitably comprises a projection lens 462, a mirror 464, and an aperture 466. Lens 462 preferably comprises a telocentric projection lens optimized for specific image sizes used on light valve 442 and rear projection screen 326. Lens 462 converges collimated beam 46û until the converging beam, after striking mirror 464, converges to a focal point, whereupon it thereafter forms a divergent beam 470 which effectively images the data corresponding to the then current data slice 14 onto projection screen 326 and onto film 319. Beam 470 passes through an aperture 466 at dp~ XirlldL~Iy the point where beam 470 reaches a focal point. Aperture 466 preferably comprises an iris diaphragm ID-0.5 manufactured by Newport. Note, however, that aperture 466 is substantially larger than the diameter of beam 470 at the point where the beam passes through aperture 466. This is in contrast to the pinhole apertures comprising beam expanders 314 and 322 which function toremove the high frequency ~""pu"~ from the beam. The high frequency components 2~ within beams 460 and 470 are important in the present invention inasmuch as they may correspond to the data which is the subject of the hologram being produced. Aperture 466 simply traps and shunts scattered light and otherwise misdirected light carried by beam 470 or otherwise visible to projection screen 326 and which is not related to the information corresponding to the data on data slice 14.
With continued reference to Figure 6, beam 470 is projected to apply a focused image onto rear projection screen 326. Screen 326 is suitably on the order of 14 inches in width by 12 inches in height, and preferably comprises a thin, planar diffusing material adhered to one surface of a rigid, ~rd~ dle~llL substrate, for example a 0.5 inch thick glass _~1_ WO 95114960 2 t 7 7 ~ 5 8 PCTIUS94/13639 sheet 472. Diffuser 472 is fabricated from a diffusing material e.g., Lumiglas-130 manufactured by Stewart Filmscreen Corporation of Torrance, California. Diffuser 472 diffuses beam 470 such that each point within beam 470 is visible over the entire surface area of film 319. For example, an exemplary point Y on beam 470 is diffused by diffuser 5 472 so that the object beam at point Y manifests a conical spread, indicated by cone Y, onto film 319. Similarly, an arbitrary point X on diffuser 472 casts a diffuse conical spread X onto film 319. This phenomenon holds true for every point within the projected image as the image passes through diffuser 472. As a result, every point on film 319 embodies a fringe pattern which encodes the amplitude and phase information for every point on diffuser 472.
Since light from every point on diffusing diffuser 472 is diffused onto the entire surface of film 319, it follows that every point on film 319 "sees" each and every point within the projected image as the projected image appears on diffuser 472. However, eachpointonfilm319necessarilyseestheentireimage,astheimageappearsondiffuser 472, from a slightly different perspective. For example, an arbitrary point Z on film 319 "sees" every point on diffuser 472. Moreover, an arbitrary point W on film 319 aiso "sees" every point on diffuser 472, yet from a very different perspective than point Z.
Thus, after emerging from diffuser 472 and polarizer 327, the diffuse image carried by object beam 473 is applied onto film 319.
Presently known diffusing screens typically comprise a sheet of plastic, glass, or the like which is either rough or which comprises particles which scatter light. Such diffusers are w~ dilled by the simple physics of particle scattering, such that very little control may be exerted over the extent and direction of the random scatterlng.
To increase the efficiency of the diffusing screen, diffusing screen 472 may 25 alternately comprise a holographic optical element (HOE).
More particularly, a hologram may be thought of as a controlled diffuser which diffuses the incoming uniform reference beam into an output of any desired pattern, which pattern may be of any desired degree of complexity.
A HOE diffuser may be conveniently constructed by applying diffused laser light 30 to a holographic film substrate. Indeed, a very high-quality conventional plastic diffusing screen, which is itself extremely inefficient, may be employed to project a diffused pattern onto the holographic film. That is, the object beam used to create the HOE simply comprises the output of a high-quality conventional diffuser. By recording a hologram of WO 95/14960 2 ~ 7 ~ 3 ~ ~ PCTIUS94113639 this diffused laser light, a very efficient holographic diffusing screen may be produced.
The HOE diffuser, being a hologram, comprises a highly efficient diffuser, which does not suffer from the inherent limitations of a conventional plastic diffuser, and particularly the undesirable scattering, absorption, and depolarizing characteristics of the conventional 5 diffuser.
Polarizer 327 is advantageously mounted on the surface of diffusing diffuser 472.
Although the light (beam 470) incident on diffusing diffuser 472 is substantially P-pold,i,dliù,, diffuser 472, by its very nature, scatters the light passing therethrough, typicdlly depolarizing some of the light. Polarizer 327, for example a thin, planer, 0 polarizing sheet, repolarizes the light so that it is in a substantially pure P-polarization state when it reaches film 319. Note that polarizer 327 is disposed after diffuser 472, so that the light improperly polarized by diffuser 472 is absorbed. This ensures that a high p~ llLd~t: of the object beam, being substantially P polarized, will interfere with the reference beam at film 319, further enhancing the contrast of each hologram.
With continued reference to Figure 6A, diffuser 472 may alternatively comprise aholographic optical element constructed in a known manner to i~l"ul~"l~"l the diffusing function. In yet a further alternative embodiment, an additional lens (not shown) may be placed adjacent to diffuser 472, for example between diffuser 472 and imaging assembly 328. Through the use of an d,l,)UlUUl idl~ lens, substantially all of the light emerging from diffuser 472 may be cdused to emerge substantially orthogonally from diffuser 472.
Consequently, the object beam may be caused to strike film substrate 319 in a substantially parallel manner, i.e., substantially all ~olll,uo~ s of the object beam strike film substrate 319 substantially o,LIlugolldlly thereto.
Returning briefly to Figure 6B, those skilled in the art will appreciate that liquid 2s crystal devices typically exhibit good contrast on the axis, with increasingly poor contrast the further off axis the liquid crystal display is viewed from. In the context of the present invention, it is highly desirable that the composite hologram exhibit high contrast from quite large angles, both up and down and from left to right. In this way, detailed analysis of the medical data may be viewed with full parallax from substantially large off-axis 30 angles in all directions. Indeed, high contrast is desirable for viewing angles of up to 30 -40 degrees off axis and greater from essentially all directions.
In accordance with an alternate embodiment of the present invention, high off-axis contrast may be achieved at the film surface by using an LCD to sequentially project each wog5/l4960 2 1 77~ ~ ~ PCTIUS94/13639 data slice on to the film. However, because of the poor off-axis contrast exhibited by typical LCD's, it is also desirable to plaoe a diffuser i~""e.lid~ly after the LCD, i.e., at the downstream surface of the LCD between the LCD and the film substrate. A lens may then be placed at the downstream surface of the diffusing screen li.e., between the diffusing 5 screen and the film surface). In this way, the high contrast on axis output of the LCD is scattered (diffused) by the diffuser, with the diffused image captured by the lens and projected on to the film. Because the image captured by the lens corresponds to the on-axis image scattered by the diffuser, the poor off-axis charaderistics of the LCD are overcome, resulting in high off-axis contrast at the film surface.
0 The manner in which the complex object wave front travelling from diffuser 472 to film 319 is encoded within the film, namely in the form of a static interferenoe pattern, is the essence of holographic reprodudion~ Those skilled in the art will appreciate that the interferenoe (fringe) pattern encoded within the film is the result of constructive and destructive interadion between the obied beam and the reference beam. That being the 5 case, it is important that the object beam and reference beam comprise light of the same wavelength. Although two light beams of different wavelengths may interact, the interadion will not be constant within a particular plane or thin volume (e.g, the "plane"
of the recording film). Rather, the interadion will be a time-varying function of the two wavelengths.
The static (time invariant) interaction between the obied and reference beams inaccordance with the pre-sent invention results from the monochromatic nature of the source of the reference and obied beams (i.e., monochromatic laser sources 302 exhibiting an adequate coherence length). Moreover, those skilled in the art will further appreciate that maximum interadion occurs between light beams in the same polarization 25 state. Accordingly, maximum interaction between the object and reference beams may be achieved by ensuring that each beam is purely polarized in the same polarization state at the surface of film 319. For films mounted in the configuration shown in Figure 6A, the present inventor has determined that P polarized light produces superior fringe patterns. Thus, to enhance the interference between objed bedm 470 and referenoe30 beam 423, beam 47 passes through polarizing screen 327 adhered to the surface of diffuser 472.
The pure P polarized reference beam 423 passes through a collimating iens 316 and is collimated before striking film 319. Inasmuch as the reference and object beams -2~

WO 95114960 ~ 7~ Pi~/US94113639 both emanate from the same laser 302, and further in view of the relatively longcoherence length of laser 302 relative to the differential path traveled by the beams from the laser to film 319, the reference and object beams incident on film 319 are mutually coherent, monochromatic (e.g, 514.5 nm), highly purely P polarized and, henoe, highly - s correlated. In addition, reference beam 423 is highly ordered, being essentially noise free and collimated. Object beam 470, on the other hand, is a complicated wave front which uiiJoldLrr~ the data from the current data slice. These two waves interact extensively withinthevolumeoftheemulsionru",u,i~i"gfilm319,producingastatic,standingwave pattern. The standing wave pattern exhibits a high degree of both constructive and 10 destructive i, llel ~el el ,ci . In particular, the energy level E at any particular point within the volume of the emulsion may be described as follows:
E -- [Ao cos Bo + Ar cos B,]Z
where Ar~ and A, represent the peak amplitude of the ûbject and reference beams,respectively, at a particular point, and Bo and Br represent, the phase of the object and 5 reference beams at that same point. Note that since the cosine of the phase is just as likely to be positive as negative at any given point, the energy value E at any given point will range from 0 to 4A2 (ArJ _ A, for a unity beam ratio). This constructive and destructive wave interference produces well defined fringe patterns.
For each data slice, film 319 will be exposed to the standing wave pattern for a20 iJle~ielellllilled exposure time sufficient to convert that data slice's pro rata share of silver halide grains.
After film 319 is exposed to the interference pattern corresponding to a particular data slice, track assembly 334 is moved forward (or, alternatively, backward) by a uleil~ellll ledamountproportionaltothedistancebetweenthedataslices. Forexample, 25 if a life size hologram is being produoed from CT data, this distance suitably corresponds exadly to the distance travelled by the subject (e.&, the patient) at the time the data slices were generated. If a less than or greater than life size hologram is being produced, these distances are varied dcrLu,dil~,,ly.
In a~uli~dl~e with a preferred ellli~odilllellt of the invention, film 319 suitably 30 comprises HOLOTEST~ holographic film, for example film No. 8E 56HD manufactured by AGFA, Inc. The film suitably comprises a gelatinous emulsion prepared on the surface of a plastic substrate. An exemplary film may have a thickness on the order of .015 inches, with an emulsion layer typically on the order of dUUlU~illldLely 6 microns.
-2s-Incontrasttoconventional,ul~ulu~;,d,ul,y,whereinamplitudeinformationpertaining to the incident light is recorded within the film emulsion, a hologram contains a record of both amplitude and phase information. When the hologram is replayed using the same wavelength of light used to create the hologram, the light emanating from the fi!m 5 continues to propagate just as it did when it was 'frozen' within the film, with its phase and amplitude information substantially intact. The mechanism by which the amplitude and phase information is recorded, however, is not widely understood.
As discussed above, the reference beam and object beam, in accordance with the present invention, are of the same waveiength and polarization state at the surface of film 10 319. The interaction between these two wave fronts creates a standing (static) wave front, which extends through the thickness of the emulsion. At points within the emulsion where the object and reference beam constructively interact, a higher energy level is present than would be present for either beam independently. At points within the emulsion where the reference and object beam destructively interact, an energy level 5 exists which is less than the energy level exhibited by at least one of the beams.
Moreover, the instantaneou3 amplitude of each beam at the point of interaction is defined by the product of the peak amplitude of the beam and the cosine of its phase at that point. Thus, while holographers speak of recording the amplitude and phase information of a wave, in pradical effect the phase information is 'recorded' by virtue of the fact that 20 the instantaneous amplitude of a wave at a particular point is a function of the phase at that point. By recording the ill~ldl)tdl~UUs amplitude and phase of the static interference pattern between the reference and object beams within the three-dimensional emulsion, a "three~' "~"siu"al picture" of the object as viewed from the plane of film 319 is recûrded. Since this record contains amplitude and phase information, a three-25 dimensional image is recreated when the hologram is replayed.
Aher every data slice ~UIIIIJli~ill~ a data set is recorded onto film 319 in theforegoing manner, film 319 is removed from film holder 318 for processing.
Asdiscussedabove7theul,ul~ld,ullicemulsionemployedinthepresentinvention comprises a large number of silver halide crystals suspended in a gelatinous emulsion.
30 While any suitably photosensitive element may be employed in this context silver halide crystals are generally on the order of 1,000 times more sensitive to light than other known phu~us~"~i~ive elements. The resulting short exposure time for silver halide renders it extremely compatible with holographic applications, wherein spurious vibrations can severely erode the quality of the holograms. By keeping exposure times short in duration for a given luer power, the effects of vibration may be minimized.
As also discussed above, a hologram corresponding to each of a plurality of dataslices is sequentially encoded onto film 319. After every slice ~u~ g a particular - 5 data set has been recorded onto the film, the film is removed from camera assembly 3ûû
for prooessing Before discussing the particular processing steps in detaiL it is helpful to understand the photographic function of silver halide crystals.
In conventional l~hùlu~d~ly, just as in amplitude holography, a silver halide crystal which is exposed to a threshold energy level for a threshold exposure time 0 becomes a latent silver halide grain. Upon subsequent immersion in a developer, the latent silver halide grains are converted to silver crystals. In this regard, it is important to note that a particular silver halide grain carries only binary data; that is, it is either converted to a silver crystal or it remains a silver halide grain throughout the process.
Depending on the processing techniques employed, a silver halide grain may ultimately 5 ~u~ Jol~d to a dark region and a silver crystal to a light region, or vice versa. In any event, a particular silver halide grain is either converted to silver or left intact and, hence, it is either "on" (logic hi) or "off" (logic low) in the finished product.
In conventional photography as well as in amplitude holography, the exposed filmis immersed in a developing solution (the developer) which converts the latent silver 20 halide grains into silver crystals, but which has a negligible affect on the unexposed silver halide grains. The developed film is then immersed in a fixer which removes the unexposed silver halide grains, leaving dear emulsion in the unexposed regions of the film, and silver crystals in the emulsion in the exposed areas of the film. Those skilled in the art will appreciate that the converted silver crystals, however, have a black 2s appearance and, henoe, tend to absorb or scatter light, decreasing the efficiency of the resulting hologram.
In phase holography, on the other hand, the exposed film is bleached to remove the opaque converted silver, leaving the unexposed silver halide grains intact. Thus, after bleaching, the film comprises regions of pure gelatinous emulsion comprising neither 30 silver nor silver halide (corresponding to the exposed regions), and a gelatinous emulsion U~ lg silver halide (~oll~ u~ding to the unexposed regions). Phase holography is predicated on, inter alia, the fact that the gelatin containing silver has a very different WO 95/14960 2 1 7 7 ~ ~ 8 PCTlllS94/13639 refractive index than the pure gelatin and, hence, will diffract light passing therethrough in a correspondingly different manner.
The resulting bleached film thus exhibits fringe patterns ~u~ g alternating lines of high and low refractive indices. However, neither material comprises opaque 5 silver crystals, so that a substantially insignificant amount of the light used to replay the hologram is absorbed by the hologram, as opposed to amplitude holographic techniques wherein the opaque silver crystals absorb or scatter a substantial amount of the light.
More particularly, the present invention contemplates a six-stage processing scheme, for example, performed on a Hope RA201 6V photoprocessor manufactured by10 Hope Industries of Willow Grove, Pennsylvania.
In stage 1, the film is developed in an aqueous developer to convert the latent silver halide grains to silver crystals, which may be made by mixing, in an aqueous solution (e.g., 1800 ml) of distilled water, ascorbic acid (e.g., 30.0 g), sodium carbonate (e.g., 40.0 g), sodium hydroxide (e.g., 12.0 g), sodium bromide (e.g., 1.9 g), phenidone 1s (e.g., 0.6 g), and distilled water resulting in a 2-liter developing solution.
In stage 2, the film is washed to halt the development process of stage 1.
Stage 3 involves immersing the film in an 8 liter bleach solution ~ul~ illg distilled water (e.g., 72û0.0 ml), sodium dichromate (e.&, 19.0 g), and sulfuric acid (e.g., 24.0 ml). Stage 3 removes the developed silver crystals from the emulsion.
Stage 4 involves washing the film to remove the stage 3 bleach.
Stage 5 involves immersing the film in a 1 liter stabilizing solution ~ g distilled water (50.0 ml), potassium iodide (2.5 g), and Kodak PHOTO-FLO (5.0 ml). The stabilizing stage .i~",i~ the remaining silver halide grains to enhance long-term stability against subsequent exposure.
2s In stage 6, the film is dried in a conventional hot-air drying stage. Stage 6 is suitably performed at 100 degrees fahrenheit; stages 1 and 3 are performed at 86 degrees rdl.,~"l":i~; and the remaining stages may be performed at ambient temperature.
Upon completion of the processing of film 319, the resulting master hologram maybe used to create one or more copies.
In accordance with one aspect of the invention, it may be desirable to produce acopy of the master hologram and to replay the copy when observing the hologram, rather than to replay and observe the master hologram directly. With reference to Figure 10, Figure 1 OA depicts a collimated replay beam PB replaying a master hologram, with beam WO95/14960 2 1 77~58 PCT/US94/13639 PB being directed at the film from the same direction as the collimated reference beam used to create the hologram (H1). This is reflected to as orthoscopic reconstruction.
This is consistent with the layout in Figure 3, wherein the data slice corresponding to respective images 1002 in Figure 10, were also illuminated onto the film from the same 5 side of the film as the reference beam. However, when observed by an observer 1004, the reconstructed images appear to be on the opposite side of the film from the observer.
Although the reconstructed images 1002 are not literally behind hologram H1, they appear to be so just in the same way an object viewed when facing a mirror appears to be behind the mirror.
0 With momentary reference to Figure 10B, hologram H1 is inverted and again replayed with the replay beam PB. In this configuration, known as r~P~ os~oric construction, the images 1002 appear to the observer as being between the observer and the film being replayed. When master hologram H1 is copied using copy assembly 900, the rSPl Idr~SfpiC construction set forth in Figure I OB is essentially reconstructed, wherein 5 the master hologram is shown as H1, and a holographic film corresponding to the copy hologram is positioned within the images 1002 in a plane P. The assembly shown in Figure 10B illustrates the copy film (plane P~ as being centered within the images 1002, thereby yielding a copy hologram which, when replayed, would appear to have half of the three-dimensional image projecting forward from the film and half the three-20 dimensional image projected back behind the film. However, in (~ UlddllU~: with an alternate embodiment of the present invention, the copy assembly may be configured such that plane P assumes any desired position with respect to the data set, such that any ~u~ Jull~i~lg portion of the three~ siv"al image may extend out from or into theplane in which the film is mounted.
25 COPY A~SEMBLY
Referring now to Figure 9, copy assembly 900 is suitably mounted to a table 904 in much the same way camera assembly 3 is mounted to table 304 as described in conjunction with Figure 3. Copy assembly 900 suitably comprises a laser source 824, respective mirrors 810, 812, 820, and 850, a beam splitting cube 818, a wave plate 816, 30 respective beam expanders 813 and 821, respective collimating lenses 830 and 832, a master film holder 834 having respective legs 836A and 836B, and a copy film holder 838 having a front surface 840 configured to securely hold copy film substrate H2 in place.

WO 95/14960 2 1 7 7 3 ~ 8 PCT/US94113639 Film holder 838 and, if desired, respective film holders 834 and 318 are suitably equipped with vacuum equipment, for example, vacuum line 842, for drawing a vacuum between the film and the film holder to thereby securely hold the film in place. By ensuring intimate contact between the film and the holder, the effects of vibration and 5 other spurious fi Im movements which can adversely impact the interferenoe fri nge patterns recorded therein may be substantially reduced.
Film holders 838 and 318 desirably comprise an opaque, non-reflective (e.g., black) surface to minimize unwanted reflected light therefrom. Film holder 834, on the other hand, necessarily comprises a Lldl~LJdl ~ surface inasmuch as the obiect beam must 0 pass therethrough on its way to film holder 838. Accordingly, the opaque film holders, may, if desired, comprise a vacuum surface so that the film held thereby is securely vacuum-secured across the entire vacuum surface. Film holder 834, on the other hand, being ~d"~Lart:"l, suitably comprises a perimeter channel wherein the corresponding perimeter of the film held thereby is retained in the holder by a perimeter vacuum s channel. A glass or other Lld~ Jdl~ t surfaoe may be conveniently disposed within the perimeter of the channel and a roller employed to remove any air which may be trapped between the film and the glass surface.
Although a preferred embodiment of the present invention employs the foregoing vacuum film holding techniques, any mechanism for securely holding the film may be 20 conveniently used in the context of the present invention, including the use of an electrostatic film holder; a pair of opposing glass plates wherein the film is lightly sandwiched therebetween; the use of a suitable mechanism for gripping the perimeter of thefilmandmaintainingsurfaoetensionthereacross;ortheuseofanairtightcellwherein ~u~LJIt:~ed air may be IlldillLdill~l within all to securely hold the film against one surface 25 of the air tight chamber, the chamber further including a bleed hole, disposed on the surface of the cell against which the film is held, from which the ~r"LJ,t ~ d air may escape.
With continued reference to Figure 9, laser source 824 is sul-tably similar to laser 302, and suitably produces laser light of the same wavelength as that used to create the 30 master hologram (e.g., 514.5 nm). Alternatively, a laser source for producing the copy may employ a different, yet ,~ lll;"ed, wavelength of light, provided the angle that the referenoe beam illuminates film H1 is varied in accordance with such wavelength.
Those skilled in the art will appreciate that the wavelength (~1) of the reference beam WO 95/14960 2 1 7 7 3 ~ 8 PCTIUS94/13639 illuminating hologram H1 is p~ nliol)dl to the sine of its incident angle, e&"l ~
K sin ~. Moreover, by manipulating the processing pdlcllll~ to either shrink or swell the emulsion, the relationship between the wavelength and the incident angle can be further adjusted in accordance with the relationship between the incident angle and a - 5 reference beam wavelength.
Asourcebeam825fromlaser824isreflectedoffmirror812throughawaveplate 816 and into cube 818. Variabie wave plate 816 and cube 818 function analogously to beam splitting assembly 310 discussed above in conjunction with Figure 3. Indeed, in a preferred e",bodi~"e,~ of the present invention, a beam splitting assembly nearly 0 identical to beam splitter 310 is used in copy system 900 in lieu of wave plate 816 and cube 818; however, for the sake of clarity, the beam splitting apparatus is schematically :p~s~t~ as cube 18 and wave plate 816 in Figure 9.
Beam splitting cube 818 splits source beam 825 into an S polarized object beam 806 and a P polarized reference beam 852. Object beam 806 passes through a wave plate 814 which converts beam 806 to a P polarized beam, which then passes through a beam expanding assembly 813 including a pin-hole (not shown); reference beam 852 passes through a similar beam expander 821. Respective beam expanding assemblies 813 and 821 are similar in structure and function to beam expanding assembly 314 discussed above in conjunction with Figure 3.
Object beam 806 emerges from beam expander 813 as a divergent beam which is reflected off mirror 850 and collimated by lens 832. Reference beam 852 is reflected off mirror 820 and collimated by lens 830. Note that virtual beams 802 and 856 do not exist in reality, but are merely illustrated in Figure 9 to indicate the apparent source of the object and reference beams, respectively. Note also that object beam 806 and reference 25 beam 852 are both pure P polarized.
The master hologram produced by camera assembly 300 and discussed above is mounted in a Lldn~a~ film holder 834 and referred to in Figure 9 as H1. A secondfilm H2, suitably identical in structure to film substrate 319 prior to exposure, is placed in film holder 838. Object beam 806 is cast onto master hologram H1 at the Brewster's 30 angle associated with film H1 ~d,u,l~lo~d~dl~ly 56).
Film substrate H2 records the standing wave pattern produced by object beam 806 and reference beam 852 is the same manner as described above in connection with film 319 in the context of Figures 3 and 4. More particularly, the plurality of images WO 9S/14960 2 ~ 7 7 3 ~ 8 PCT/US94/13639 ~ulle~,uO~ g to each data slice within a data set are simultaneously recorded onto film H2. The amplitude and phase information ~ulle~,uu~ ; to each data slice is accurately recorded on film H2 as that amplitude and phase information exists within the plane defined by film H2. When copy hologram H2 is subsequently replayed, as discussed in 5 greater detail below, the image ~ulle~JOI~Jillg to each data slice, with its amplitude and phase ill~lllldLiull intact, accurately recreates the three-dimensional physical system defined by the data set.
It will be duple~idled that large collimating lenses such as refe~ence beam collimating lens 316 (Figure 3) are quite expensive. Although it is desirable in aordance 0 with the illustrated ellluC ' "~"L to employ a collimated reference beam and a collimated object beam, one or both of the reference and object beam collimating lenses may be dispensed with in the context of an alternating embodiment.
More particularly, a divergent reference and/or object beam may be employed as opposed to two collimated reference and object beams in accordance with an alternate embodiment of the present invention. It is generally known, however, that the use of such divergent beams may result in distorted images at the film plane. However, the nature and extent of these distortions may be fairly precisely modeled and quantified.
See, for example, the discussion by Edwin Champagne in the January, 1967 issue of the Journal of Eledrical Society of America.
Specifically, by calculating the manner in which the use of one or more divergent beams will distort the image at the fi!m plane, the date embodied in a data slice may be manipulated mathematically to ~ulllluellsdle for this distortion. In this way, a properly recûnstructed image may be obtained at the film surface notwithstanding the use of non-collimated reference and/or object beams.
With continued reference to Figure 9~ the present inventor has deLe~ l leu that the emulsion .u",~,i,i"g the film within which holograms are made in accordance with the present invention may undergo subtle volumetric changes during processing. In particular, the emulsiûn may shrink or expand on the order of 1% or more, depending upon the particular chemistry involved in processing the substrate.
Although such shrinkage or expansion has a relatively minimal effect on a masterhologram, this effect may be eXd~;el dLed in the conte~a of a copy hologram. Specifically, a 1% shrinkage in a typical hologram on the order of, for example, 10 ~ellLillleLel~ may be il"~Je,~e~Lible to the observer; however, when the master hologram (H1) is copied WO95/14960 2 ~ 7735~ PCTIUS94113639 onto a copy hologram (H2), a 1% change in master hologram H1 may manifest itself as a 1% change in the distance between master hologram holder 834 and copy hologramholder 838, which distance is generally far greater than the actual size of the hologram.
Indeed,fora141/2inchseparationbetweenmasterfilmholder834andcopyfilmholder 5 838, a 1% shrinkage in the substrate ~uil~,ulisillg hologram H1 may result in the copy hologram being displaced from the film plane on the order of 5 millimeters.
To correct for such shrinkage/expansion and thereby ensure that copy hologram holder 838 H2 closely corresponds to the film plane of the hologram, the distance between master hologram holder 834 and copy hologram holder 838 may be suitably 0 manipulated. In particular, if the emulsion ~ù",,~,,isi"~ master hologram H1 shrinks by, for example, 1%, the distance between master hologram holder 834 and copy hologram holder 838 may be suitably decreased by ap,ulu~i"~d~ 1%. Similarly, to the extent the emulsion ~u",,ur;~i"g the master hologram expands during processing, the foregoing distance may be correspondingly increased.
Moreover, the distance between master hologram holder 834 and copy hologram holder 838 may also be manipulated such that copy hologram holder 838 cuts through any desired position in the hologram. In particular, while it is often desirable for the copy hologram to straddle the film plane, i.e., for dpu,u~ill,d~ly one-half of the holographic image to be projected in front of the viewing screen and one-half of the hûlogram to be 20 projected behind the film screen, by manipulating the distance between the master hologram holder and the copy hologram holder any desired portion of the hologram may be positioned in front of or behind the film plane, as desired.
In the preferred embod iment discussed herein, master holograms H 1 are producedon a camera assembly 300, and copy holograms H2 are produced on a copy assembly 25 900. In an alternate embodiment of the present invention, these two systems may be conveniently combined as desired. For example, film holder 318 in Figure 3 may be replaced with film holder 834 from Figure 9, with a subsequent H2 film holder disposed such that the object beam is l~dn~",.ll~i through film holder 834 onto the new H2 film holder. In this way, the relationship between film holders H1 and H2 (Figure g) would 30 be substantially replicated in the hybrid system. To complete the assembly, an additional reference beam is confined to strike the new H2 film holder at Brewster's angle. As altered in the foregoing manner, the system can effectively produce master holograms and copies on the same rig. More particularly, the master hologram is produced in the WO9S/14960 2177~58 PCT/US94/13639 manner described in conjunction with Figure 3 and, rather than utilizing a separate copy rig, the master hologram may simply be removed from its film holder, inverted, and utilized to create a copy hologram. Of course, the original object. beam would be shunted, and replaced by a newly added reference beam configured to illuminate newly 5 added film holder H2.
In yet a further ~ "l,~ ' "~"L of the present invention, which master holograms may be produced substantially in a.~u,dd,~ with the foregoing discussion copy holograms may be suitably produced through a method known as contact copying. Specifically, a master hologram (H1) may be placed in intimate contact with a suitable sheet of film and 0 a reference beam applied thereto, as is known in the context of producing copies of conventional holograms.
As discussed above, a master hologram (H1) produced in accordance with the illustrated embodiment results in a non-image plane hologram; the copy assembly described herein may thus be employed to generate an image planed hologram (H2) from the master hologram. Alternatively, various apparatus and techniques may be employed to generate an image planed hologram in a single step.
More particularly and with momentary reference to Figure 3, in the preferred embodiment discussed above, the images corresponding to the slices are projected from screen 472 on to film holder 319 at a variable distance in the range of, e.g., 14 inches.
20 Alternatively, the projedion assembly may be brought very close to the film surface, such that some of the data slices (e.g., half of them) are projected on to one side of the film and, after turning the film over (and rotating it by 180 degrees) and projecting the remaining slices on to the other side of the film. In this way, an image planed hologram may be theoretically produced. However, it becomes difficult to apply a reference beam 2s at a desired reference angle (e.&, Brewster's angle) to the film surface, in view of the close proximity of the projedion assembly to the film plane.
Referring now to Figure 12, a diffusing screen 1202 may be advantageously disposed very close to Film 319, such that the object beam 1204 applied to the input service of diffusing screen 1202, is diffused onto the film. In accordance with the 30 ~",L,odi",e"lshowninFigure 12~diffuserl2o2issuitablyd~iso~,upi~thatis~screen12o2 fundions as a diffuser when object beam 1204 is applied to it, whereas screen 1202 permits reference beam 1206 to pass through it in a substantially ~Idl~,Jdlt~ manner. In this regard, such an angle defective diffuser may be conveniently fabricated as a WO95/14960 2 ~ 7735~ PCIIUS94113639 holographic optical element, such that it functions as diffuser for the object beam, yet acts like a lld~ dl~ window with respect to the reference beam.
By properly configuring and positioning such a lens, the image on the projectionscreen (i.e., diffuser 47~) may be focused on to film 319. By moving the projection 5 assembly along track assembly 334 to thereby vary the distanoe between the diffusing screen/lens assembly and the film plane, the relative positions of the data slices within a data set may be preserved. However, the image for a particular slice will not necessarily be focused at the plane of the film substrate; rather, the image for each slice will be focused at a point in front of or behind the film substrate in accordance with the relative 0 position of the particular data slice in the data set. However, sinoe the film substrate will capture the phase as well as amplitude information of each slice, a properly positioned and properly focused image will be produced for each data slice upon replay of the finished hologram. Moreover, by properly configuring the d~u,~"l~"lioned lens, an image planed hologram may be produced in a single step.
In accordance with a further alternative ~ Ludilllellt, to reduce the size, weight, and cost of such a projection lens, a HOE lens may be employed.
More particularly, such a HOE lens may be made by creating a hologram of a point source of light, for example a spherically irradiating point source. When the HOE
lens is replayed, the output of the HOE lens will converge to the point source, effectively 20 focusing light from a parallel beam to a point. As such, the HOE lens functions in a manner optically equivalent to a conventional glass lens.
As also discussed above, the present invention contemplates, for a data set comprising N slices, recording N individual, relatively weak holograms onto a single film substrate. To a first d~uplukilllaLiul~ each of the N slices will consume (convert) 25 a,u~nukillldl~ly 1/N of the available silver halide grains consumed during exposure.
As a starting point, the total quantity of photosensitive elements within a filmsubstrate may be inferred by sequentially exposing the film, in a conventional photographic manner, to a known intensity of light and graphing the extent to which silver halide grains are converted to silver grains as a function of applied energy (intensity 30 multiplied by time). At various time intervals, the extent to which the film is fogged, i.e., the extent to which silver halide grains are converted to silver grains, is measured by simply exposing the film to a beam of known intensity, developing the film, and measuring the amount of light which passes through the film as a function of incident WO 95/14960 2 1 7 7 ~ 5 8 PCT/I~S94113639 light. Although typical HD curves are nonlinear, they may nonetheless be used in the context of the present invention to ascertain various levels of fog as a fundion of applied energy.
In accordance with the present invention, the HD curve for a particular film 5 (generally supplied by the film manufadurer) may be used to determine the amount of light, expressed in microjoules per square cm, necessary to prefog the film to apredetermined level, for example, to 10/0 of the film's total fog capacity as determined by the HD curve. After prefogging the film to a known level, a very faint, plane grating hologram is recorded onto the film, and the diffradion efficiency of the grating measured.
0 Thereafter, a different piece of film from the same lot of film is prefogged to a higher level, for example to 20% of its total fog capacity based on its HD curve, and the same faint hologram superimposed on the fogged film. The diffradion efficiency of the faint hologram is again measured, and the process repeated for various fog levels. Thee diffraction efficiency of the grating for each fog level should be essentially a function of 15 the pre-fog level, inasmuch as the prefogging is wholly random and does not produce fringe patterns of any kind.
A particular film lot may be conveniently characteri~ed in terms of its multipleexposure holographic exposure capacity. For a data set ~u"",,i~i"g N slices, the film's total exposure capacity may be conveniently divided into N equal amounts, such that 20 each data slice may consume 1/N of the film's total exposure capacity. Recalling that the energy for a particular slice is equal to the product of the intensity of the incident light and time of exposure, and further recalling that the intensity of the incident light (e.g., object beam~ is determined for eaçh slice in the manner described below in connedion with the beam ratio determination, the time of exposure for every slice may be 25 conveniently d~L~" "i"ed.
In a.~u,dd".~ with a further aspect of the present invention, each lot of film may be conveniently coded with data ~u~ Jondi~g to its total exposure capacity and/or dl diffraction effficiency. Analogously, most conventional 35 mm film is encoded with certain information regarding the film, for example, data relating to the 30 exposure ~l,a,d~L~ Lics of the film. In a similar way, the information pertaining to the film's diffraction efficiency curve may be conveniently appended to each piece of holographic film for use in the present invention, for example by applying it to the film or to the packaging therefor. The computer (not shown) used to control camera assembly WO 95J14960 2 1 773~ PCT/US94/13639 300 may be conveniently configured to read the data imprinted on the film, and may thereafter use this data to compute the exposure time for each data slice in the manner described herein.
As stated above, the relative intensities of the reference beam to the object beam at the film plane is known as the beam ratio. Known holographic techniques tend to define beam ratio without reference to a polarization state; however, an alternate definition of the term, particularly in the context of some aspects of the present invention, surround outside the relative intensities of the reference and object beams (at the film plane) at a particular common polarization state, i.e., either a common P polarization state 0 ora common S portion state. Moreover, beam intensity, for purposes of determining beam ratio, may alternatively be defined in terms of any other desired ~I,dld~ c or quality of a beam, for example by monitoring the mode of a beam through the use of a mode detector, or by monitoring beam uniformity, i.e., the amplitude of the beam a cross-section of the beam.
The intensity of a beam may be suitably detected at the film surface through theuse of a photo-diode. In accordance with one aspect o:f the present invention, one or more photo-diodes may be suitably embedded in a convenient location within the hardware ~o,~ ,g camera system 300, for example, as part of film holder 319 In this regard, such a photo-diode may be embedded on the perimeter of the film holder (to the 20 side of the film) or within the film holder itself, behind the transparent film Alternatively, one or more photo-diodes may be suitably disposed on arms or similar lever mechanisms which may selectively inserted into and removed from the beam path, as desired.
For purposes of understanding the role of beam ratio in the present invention, it is helpful to point out that holography may be conveniently divided into display25 holography, in which the hologram is intended to show a three~ "siol~al image of a selected object, and Holographic Optical Elements (HOE) in which a basic holographic fringe pattern is recorded on a film which thereafter functions as an optical element having well-defined properties, for example, as a lens, mirror, prism, or the like HOEs are formed with simple directional beams leading to simple repetitive fringe 30 patterns which tend to dominate weak secondary fringes which are also formed by scattered and reflected light within the emulsion Since the secondary fringe patterns are typically ignored to the first approximation, conventional holographic theory states that wo95/14960 2 1 77 ~58 PCT/US9~/13639 to achieve the strongest interference between the two beams, a beam ratio of one should be employed.
In display holography, on the other hand, while the reference beam is still a simple directional beam, the object beam can be extremely complex, having intensity and5 direction variations imposed by the object. In addition, objects typically exhibit any number of bright spots which diffuse light at fairly high intensities.
The resulting fringe pattern is extremely complex, bearing no simple relationship to the object being recorded. Moreover, the bright spots (highlights) on the object act as secondary reference beams, producing unwanted fringe patterns as they interfere 0 with the reference beam and with each other, resulting in many sets of noise fringes, effectively reducing the relative strength of the primary fringe pattern. The resulting "intermodulation" noise (also referred to as self-r~r~ "~i"g noise) causes an unacceptable loss of image quality unless it is suppressed.
Conventional holographic theory states that intermodulation noise may be 5 suppressed by increasing the relative strength of the reference beam, with respect to the object beam, by selecting a beam ratio in the range of 3 to 30, and most typically between 5 and 8. This results in strong primary fringes and greatly reduced secondary fringes (intermodulation noise). Thus, existing holographic techniques suggest that, in the context of display holography, a beam ratio higher than unity and preferably in the range 20 of 5-8:1 substantially reduces intermodulation noise.
The diffraction effici-ency oFa hologram, i.e., how bright the hologram appears to an observer, also exhibits a maximum at a beam ratio of one. At beam ratios higher than one, the diffraction efficiency falls off, resulting in less bright holograms when replayed.
The conventional wisdom in existing holographic theory, however, states that since 2s intermodulation noise falls offfaster than diffraction efficiency as the beam ratio increases, a beam ratio of between 5-8:1 minimizes intermodulation noise (i.e., yields a high signal to noise ratio) while at the same time producing holograms exhibiting reasonablediffradion efficiency.
In the context of the present invention, a very low reference-to-object beam ratio, 30 for example on the order of 3:1 and particularly on the order of unity, is desirably employed, resulting in optimum (e.g., maximum) diffraction efficiency for each hologram associated with every data slice in a particular data set. In the context of the present invention, however, intermodulation noise (theoretically maximum at unity beam ratio) W0 95/14960 2 ~ ~ ~ 3 5 8 PCTIUS94113639 does not pose a significant problem as compared to conventional display holography More particularly, recall that intermodulation noise in conventional l1oluE;Idplly results from, inter alia, bright spots associated with the objects. In the present invention, the "objects" ~u.,~,uu"d to a two~lil.., ,.siu"al, windowed, gamma-corrected (discussed 5 below) data slice. Thus, the very nature of the data employed in the context of the present invention results in inherently low intermodulation noise, thus permitting the use of a unity beam ratio and permitting maximum diffraction efficiency and very high signal to noise ratio images.
Moreover, the selection of a near-unity or unity beam ratio for each slice in a data 0 set may be accomplished quickly and efficiently in the context of a preferred embodiment of the present invention.
More particularly, variable wave plate 404 may be calibrated by placing a photo-diode in the path of the reference beam near film 319 while shunting the object beam, and vice versa. As the applied voltage to wave plate 4û4 is ramped up at p,~:d~le.".i,.ed 5 i.~ , from ~ero to a maximum value, the intensity of the reference beam may be""i,.ed as a function of input voltage. Since the intensity of the reference beam, plus the intensity of the object beam (before a data slice is in~uruu. dl~d into the object beam), is a,up,uAi,,,d~ly equal to the intensity of their common source beam and the intensity of the common source beam is readily a~u:,LdillaL,lc, the pure object beam intensity as a 20 Function of voltage applied to wave plate 4û4 may also be conveniently derived. It remains to determine the proper input voltage to wave plate 404 to arrive at a unity beam ratio for a particular slice.
At a f~.,dd",el~tdl level, each data slice comprises a known number of "pixels"
(although not literally so after having passed through imaging assembly 328), each pixel 25 having a known grey level value. Thus, each data slice may be assigned a brightness value, for example, as a percent of pure white. Thus, the particular voltage level required to obtain a unity beam ratio for a particular data slice having a known brightness value may be conveniently determined by selecting the unique voltage value corresponding to a pure object beam intensity value which, when multiplied by the brightness value, is 30 equal to the reference beam intensity value for the same voltage level. This computation may be quickly and efficiently carried out by a conventional computer programmed in accordance with the relationships set forth herein.

Accordingly, each data slice has associated therewith a voltage value ~u~ olldillg to the input voltage to wave plate 404 required to achieve a unity beam ratiû~
With momentary reference to Figure 6A, as the diffusing screen is placed further5 frûm the film substrate, the object beam intensity at the film surface becomes more uniform. Conversely, as the diffusing screen gets closer and closer to the film surface, the object beam at the film surface becomes less uniform, i.e., localized regions of high intensity and low intensity may be observed as a function ûf the particular data ~urlluli~illgtheobjectbeam~notwi~ ldl~dil)gthepresenoeofevenlyrelativelyhigh-quality 10 diffusers.
In order to enhance control of the beam ratio at the film surface, it may be desirable to modulate the reference beam intensity (amplitude) distribution to more closely correspond to the obied beam intensity distribution at the film surface. Enhanced control of the beam ratio at the film surface is particularly advantageous when producing 15 a copy (H2), but may also be helpful to a lesser extend in the context of the master (H1) hologram.
At a first level of d,UUlU~illld~iOn, the intensity distribution of the referenoe beam over a cross-section of the reference beam may be modeled as a Gaussian distribution (see, e.g., Figure 5). Thus, in accordance with one ~",uuuilll~ of the present invention, 20 the reference beam at the film surface may exhibit an essentially Gaussian intensity distribution, such that a different beam ratio will be observed near the center of the film than may be observed at the outer edges of the film.
Thismaybecorrectedtoafirst-levelofapproximationbyin...,~uldli,,gafilter(not shown) into the reference beam, which filter is configured to flatten out the Gaussian 25 intensity distribution within a cross-section of the reference beam. In particular, such a filter may be configured to minimally suppress (e.g, absorb, scatter, or redirect) the beam near the outer edges of the film, while more substantially suppressing the beam near the center of the film. In this way, a substantially uniform reference beam intensity distribution may be obtained at the film surface, thereby resulting in a more uniform beam 30 ratio at the film surface.
In d~Ul~d~ with an alternate embodiment, the reference beam intensity distribution may be modulated through the use of a SLM or similar device interposed into the reference beam. The intensity distribution within the object beam at the film surface ~o-WO 95/14960 2 ~ 7 7 3 5-8 PCT/US94/13639 .
may also be measured, inferred, or calculated in any convenient manner, for example, through the use of a video camera or otherwise photo-voltaically or photo-optically measuring the object beam brightness level at various points on the film surface. Having d,.e~ i ~ed the intensity distribution in the object beam at the film surface, this 5 illtUIIIIdtiOII may be fed back into the SLM in the reference beam, such as the SLM
modulates the reference beam in a-~,,Jd"-~ with the intensity distribution of the object beam at the film plane. This permits substantially improved control over the localized beam ratio across the film surface.
Alternatively, the reference beam projection optics may be configured to expand 10 the cross-section of the beam and to clip the relatively low intensity perimeter of the beam, for example by electronically, optically, or mechanically masking the outer edges of the beam, leaving the expanded higher intensity portion of the middle of the beam intact.
In a further alternative embodiment, a SLM, LCD, or similar functional device may 5 be interposed in the reference beam, and configured to ~,"I~ dl~ for the Gaussian or other reference beam intensity distribution, for example by making the LCD dark in the middle and lighter at the edges, in radial fashion, to thereby flatten the intensity distribution of the reference beam. In this way, the SLM may be configured to implement the function of an apedizing filter. As a further alternative, a glass filter which is darker 20 in the middle than at the edges may be interposed in the reference beam, either alone or in combination with a SLM for controlling the intensity distribution of the reference beam.
In a further alternativeembodiment, the intensity distribution of the reference beam may be manipulated optically, for example, through the use of a lens or series of lenses to redirect portions of the reference beam to achieve a substantially uniform cross-25 sectional intensity distribution.
Inyetafurtheralternatee",L,o~i",t"l,theintensitydistributionoftheobjectbeam atthefilmsurfacemaybecalculatedbasedonthevariousphysicalandopticall.d,~,",~associated with the hologram camera and/or copy assembly.
More particularly, for a given data slice applied to diffusing Screen 472, the 30 intensity distribution at the input of Screen 472 may be derived as a function of the data on the slice and the optics employed to project the image onto Screen 472. In conjunction with, inter alia, the known optical properties of diffusion Screen 472, the distance between the diffuser and film plane, and the optical properties of any polarizers Il -WO 95/14960 2 1 7 7 3 5 8 PCT/lJS94113639 or other hardware employed in the projection optics, the intensity distribution at the film plain may be conveniently computed, at least to a l~d~UlldLI~ dU,UlU~CillldliUII.
In accordance with another aspect of the present invention, each data slice ~u""u,i~i"g a data set may be ~urther prepared subsequent to the windowing procedures s set forth above. In particular, imaging assembly 328 generates an image ~ur"uli,illg various brightness levels (grey levels) in accordance with data values applied to CRT 444.
However, it is known that conventional CRTs and conventional light valves do notnecessarily project images having brightness levels which linearly correspond to the data driving the image. Moreover, human perception of grey levels is not necessarily linear.
10 For example, while a image having an arbitrary brightness value of 100 may look twice as bright as an image having a brightness value of 50, an image may require a brightness level of 200 to appear twice as bright as the image having a brightness value of 100.
Because human visual systems generally perceive brightness as an exponential function, and CRTs and hot valves produce images having brightness which are neither 5 linearly nor exponentially related to the levels of the data driving the images, it is desirable to perform a gamma correction on the data slices after they have been windowed, i.e., after they have been adjusted at a gross level for brightness and contrast levels. e,y gamma correcting the windowed data, the grey levels actually observed are evenly distributed in terms of their perceptual differences.
In accordance with a preferred embodiment of the present invention, a gamma lookup table is created by displaying a series of ,u~d~L~ ;"ed grey level values with imaging assembly 328. A photo-diode (not shown) is suitably placed in the path of the output of imaging assembly 328 to measure the actual brightness level corresponding to a known data value. A series of measurements are then taken for different brightness 2s levels corresponding to different grey level data values, and a gamma lookup table is constructed for the range of grey values exhibited by a particular data set. Depending on the degree of precision desired, any number of grey level values may be measured with the photo-diode, allowing for computer interpolation of brightness ievels for grey values which are not measured optically.
Using the gamma lookup table, the data corresponding to each data slice is translated so that the brightness steps of equal value in the data correspond to visually equivalent changes in the projected image, as measured by the photo-diode duringcreation of the lookup table.
~2-WO 95/14960 2 ~ 7 7 3 ~ ~ PCT/U594/13639 Moreover, light valve 442, when used in conjunction with wave plate 463 as discussed in the context of Figures 7-8, is typically capable of producing a blackest black image on the order of about 2000 times as faint as the brightest white image. This level of contrast range is simply ~""e.~d,y in view of the fact that the human visual system 5 can only distinguish within the range of 50 to 100 grey levels within a single data slice.
Thus, the maximum desired contrast ratio (i.e., the brightness level of the blackest region on a slice divided by the brightness level of the brightest white region on a slice) is desirably in the range of 10020:1, allowing for flexibility at either end of the brightness scale. Since the contrast ratio of a particular slice is thus on the order of one-tenth the 0 available contrast ratio producible by the right valve, a higher aspect of the gamma correction scheme employed in the context of the present invention surrounds defining absolute black as having a brightness level equal to zero. Thereafter, a subjective determination is made that the darkest regions of interest on any slide, i.e., the darkest region that a radiologist would be interested in viewing on a slice, would be termed 5 "nearly black." These nearly black regions would be mapped to a value which is on the order of 100-200 times fainter than pure white. Moreover, any values below the nearly black values are desirably clamped to absolute black (zero grey value). These absolute black regions or super black regions comprise all of the regions of a slice which are darker than the darkest region of interest.
An additional gamma correction step employed in the present invention surrounds clamping the brightest values. Those skilled in the art will appreciate that conventional CRTs and light valves are often unstable at the top of the brightness range. More particularly, increasing the brightness level of data driving an image in any particular CRTAight valve combination above the 90% brightness level may yield images having 2s very unpredictable brightness levels. Thus, it may be desirous to define the upper limit of brightness level for a data set to coincide with a p,~dt:~""",ed brightness level exhibited by imaging assembly 328, for example, at 90% of the maximum brightnessproduced by imaging assembly 328. Thus, pure white as reflected in the various data slices will actually correspond to 10% less white than imaging assembly 328 is 30 theoretically capable of producing thereby avoiding nonlinearities and other instabilities associated with the optical apparatus.
Finally, if any slice is essentially black or contains only irrelevant data, the slice may be omitted entirely from the final hologram, as desired.
~3-WO 9S/14960 2 1 7 7 3 ~ 8 PCT/IJS94/13639 Thus, in a~u,.ld~ with one aspect of the present invention, the intensity of theobject beam may suitably be controlled as a function of one or more of a number of factors, including, inter alia, the voltage level applied to wave plate 404, the data distribution for a particular data slice, the axial position of a data slice with respect to the 5 film holder, and the effects of gamma correction performed on the data.
As discussed above, the exposure time for each data slice may be conveniently dt:Le"" ,ed as a function of one or more pdldlllt~ , including the desired beam ratio, the total number of slices in the data set, and the aggregate gray scaie value (brightness level) for a particular data slice. In accordance with one aspect of the present invention, 0 relatively bright slices require a relatively short exposure time, whereas relatively faint (dark) slices require a longer exposure time. In this way, each slice may thus consume an app~uplid~ (e.g., proportional) share of pl~u~u~ ive elements within the filmemu Ision.
Relatively long exposure times may be disadvantageous in several respects. For example, the longer the exposure, the more likely it is that spurious phenomena may adversely effect the quality of the hologram. Such spurious effects include, among other things, vibration, drift in beam intensity or in various projection optics Udldlll~ 15, temperature, humidity, coherence length of the laser source, and the like. It may thus be desirable to reduce the exposure time for relatively faint slices.
In accordanoe with one aspect of the present invention, the exposure time for some or all of the slices ~.ulll,uli~il,g a particular data set may be reduoed by artificially boosting the aggregate brightness level for one or more of the slices by a ,ul~d~ ed amount. This is suitably accomplished by i~ ,uo~illg phantom bright pixels to the slice, in a minimally intrusive manner.
For example, an asteroid may be placed in a dark region of the slice remote fromthe relevant data. In this way, the aggregate brightness level for a particular slioe may be boosted without affecting the brightness levels of the pixels which comprise the relevant data embodied in the slice.
In a..u,dd"-~ with a further aspect of the foregoing asteroid technique, the 30 phantom brightness regions may take any desirable form or shape, but are preferably configured as clouds, asteroids, or other random (e.g., irregular) shapes. In this regard, the use of regular shapes having sharp contrast edges (e.&, rectangular shapes) may result in undesirable side effects. For example, to the extent similar geometric patterns appear WO 9~/14960 2 1 7 7 ~ ~ ~ PCT/US94/13639 from slice-to-slice, erroneously strong or weak fringes for this pattern may be inadvertently produced. This may result in aliasing, undesired intermodulation noise, or the like.
As discussed in greater detail below, once a composite hologram (master hologram) is produced it may be desirable to make a copy of the master hologram, which s copy is suitably an image plane hologram. In this context, it may be desirable to mask the various asteroids such that they do not appear on the image plane (copy) hologram.
- This may be done by simply physically masking the holographic asteroids to optically isolate them from the copy mechanism. In this regard, masking of the holographicasteroids is facilitated if all of the asteroids for the various slices within a data set fall 10 within a single plane, for example, in the plane of the filmholder for the copy hologram (discussed in greater detail below in conjunction with Figures 9 and 10). In order to facilitate the placement of all asteroids in a single plane, it may be desirable to project the asteroids onto the master hologram from a fixed location for all slices; that is, as ~he camera assembly moves relative to the master hologram film plane as the master hologram 5 is produced, it may be desirable to maintain the asteroid projection mechanism (e.g., the variable intensity polarizer discussed above) at a fixed location corresponding to the H2 (copy hologram) film plane during production of the H1 (master) hologram.
By artificially boosting the brightness level for faint slices in accordance with the foregoing asteroid technique, the dynamic brightness range among the various slices may 20 be desirably reduced, such that the range of exposure times for the various slices ~u"~ isi~g a particular data set may also be reduced.
In a typical data set, it may be desirable to artificially boost the brightness level of only those data slices falling below a predetermined aggregate brightness threshold.
Alternatively, it may also be desirable to add an asteroid to even the brighter (i.e., high 2s gray scale value) slices, for example preserve the relative aggregate gray scale levels for the various slices comprising the data set or if all data slices within a particular data set are too faint. In this regard, it should be noted that the brightness level of each asteroid may be selected to boost each slice to a desired gray scale value.
By adding an asteroid to a relatively faint data slice, it is believed that the fringe 30 patterns produced in the film substrate for a particular data slice will be sharper and, hence, a higher contrast ratio for each data slice will be achieved, thereby producing a sharper composite hologram. This is so even though the gray scale values for the various pixels ~,",~ i"g the relevant data under examination for each data slice remains ~s- ~

WO 9~/14960 - ~ 1 7 ~ 8 PCT/US94/13639 unaltered. That is, by adding an asteroid to a faint data slice, the fringe pattern for that data slice is enhanced even though the amount of light passing through the pixels which comprise the relevant data remains unchanged.
Viewin~ Assemblv Copy hologram H2 is suitably replayed on a viewing device such as the VOXBOX~
viewing apparatus manufactured by VOXEL, Inc. of Laguna Hills, California. Certain featuresoftheVOXBOX~viewingapparatusaredescribed in U.S. Patent Nos. 4,623,214 and 4,623,215 issued November 18, 1~86.
Referring now to Figure 11, an exemplary viewing apparatus 1102 suitably 0 comprises a housing 1104 having an internal cavity 1106 disposed therein, housing 1104 being configured to prevent ambient or room light from entering the viewing device.
Viewing apparatus 1102 further comprises a light source 1108, for example a spherically irradiating white light source, a baffle 1132, a mirror 1134, a Fresnel lens 1110, a diffraction grating 1112, and a Venetian blind 1114 upon which copy hologram H2 is conveniently mounted. Venetian blind 11 t4 and hologram H2 are schematically illustrated as being separated in space from diffraction grating 1112 for clarity, in a preferred embodiment of the device, Fresnel lens 1110 suitably forms a portion of the front surface of housing 1104, diffraction grating 1 1 t 2 forms a thin, planar sheet secured to the surface of lens 1110, and Venetian blind 1 114 forms a thin planar sheet secured to grating 1112. Hologram H2 is suitably removably adhered to Venetian blind 1114 by any convenient ",~ dll~ for example by suitable clips, vacuum mechanisms, or anyconvenient manner which permits hologram H2 to be intimately yet removably bonded to the surface of Venetian blind 1114.
Fresnel lens 1110 collimates the light produced by light source 1108 and directs2s the collimated through diffraction grating t 112. The desired focal length between source 1108 and lens 1110 will be determined by, inter alia, the physical dimensions of lens 1110. In order to conserve space and thereby produce a compact viewing box 1102, the light from source 1108 is suitably folded along its path by mirror 1134. Since source 1108 may be placed near lens 1110 in order to maximize space utilization, baffle 1132 30 may be conveniently disposed intermediate source 1108 and lens 1110, such that only light which is folded by mirror 1134 strikes 1110. As discussed above, the relationship between this angle and wavelength are similarly governed by the equation ,1 ~s K sin e.
~6-WO 95114960 2 ~ 7 7 3 5 B PCTIUS94/13639 In a preferred embodiment of the present invention, the focal length of lens 1110 is approximately 12 inches.
Diffraction grating 1112 suitably comprises a holographic optical element (HOE),for example one produced by a holographic process similar to that described herein.
More particularly, diffraction grating 1112 is suitably manufactured using a reference and an object beam having a wavelength and incident angle which ~o"t~ to that used in producing hologram H2 (here 514.5 nm~. In a preferred embodiment, diffractiongrating 1112 is advantageously a phase hologram.
Diffraction hologram 1112 suitably diffracts the various components of the white0 light incident thereon from source 1 108 as a function of wavelength. More particularly, each wavelength of light will be bent by a unique angle as it travels through diffraction grating 1112. For example, the blue component of the white light will bend through an angle P; the higher wavelength green light component is bent at a greater angle Q; and the higher wavelength red light is bent at an angle R. Stated another way, diffraction 5 grating 1112 collimates each wavelength at a unique angle with respect to the surface of the grating. Those skilled in the art will appreciate, however, that diffraction grating 1112 is an imperfect diffractor; thus, only a portion of the incident light is diffracted (e.g., 50%), the remainder of the ulldirr d-~td light passes through as collimated white light.
Venetian blind (louvers) 111 4 comprises a series of very thin, angled optical slats 20 which effectively trap the undiffracted white light passing through grating 1112. Thus, substantially all of the light passing through louvers 1114 passes through at an angle, for example the angle at which the light was diffracted by grating 1112. Of course, a certain amount of light will nonetheless be deflected by the louvers and pass through at various random angles.
2s Moreover, the geometry of the slats comprising louvers 1114 may be selected to produce a resulting hologram with optimum colorization. More particularly, the slat geometry may be selected so that certain wavelengths pass through louvers 1 114 essentially intact (the nominal wave band), whereas wavelengths higher or lower than the nominal wavelength will be clipped by the louvers. Moreover, the geometry of the 30 slats may be selected such that light which passes through grating 1112 undiffracted does not pass directly through louvers 111 4. By ~ooldilldli"g slat geometry, undiffracted light may be substantially attenuated, for example, by causing such undiffracted light to reflect a number of times (e.g., four) between adjacent slats before reaching hologram H2.
~7~

wo 95~l4960 2 1 7 ~ 3 5 8 Pcr/uss4/l3639 Louvers 1114 suitably comprise a thin, pianar light control film manufactured bythe 3M Company. On one surface, louvers 1114 are slightiy convex; moreover, a greasy or waxy substance is apparently applied to this surface by the manufacturer. To avoid damage to the delicate slats, it may be desirabie to adhere the louvers to a protective 5 surface, for example, an acrylic sheet (not shown). Improper application of the "greasy"
side of louvers 1114 to an acrylic sheet may, however, produce a nonuniform contact interface between the two surfaces, which could produce undesirable optical characteristics.
The present inventor has determined that applying a thin coating to a high-lubricity 0 particulate substance (e.g., talc) at this interface tends to yield a contact surface between the acrylic sheet and the louvers having improved optical ~l,a,d.~ cs.
Hologram H2 is illustratively placed onto the viewing screen, for example by adhering it to the surface of louvers 1 114. In this regard, the viewing screen suitably comprises one or more of the following components. Iens 1110; grating 1112; and s Venetian blind 1114. Alternatively, the viewing screen may simpiy comprise a thin, planar sheet of L~d"~a,~"l material for example glass, upon which one or more of the foregoing components may be conveniently mounted. In accordance with one aspect of the present invention, such a viewing screen is suitably on the order of 10 to 16 inches in width, and on the order of 14 to 20 inches in height, and most preferably on the order 20 of 1~ by 17 inches. Consequently, it is also desirable that the various holograms made in accordance with the present invention, namely master hologram H 1 and copy hologram H2, be of suitable dimensions so that they are either smaller than or a~ i",~.~.'y as large as the viewing screen. In a particularly preferred embodiment master hologram H1 and copy hologram H2 each are suitably 14 by 17 inches.
Since hologram H2 is suitably produced using the same wavelength and reference beam angle as was used to produce grating 1112, light passing through hologram H2 is bent in accordance with its wavelength. Specifically, blue light is bent at an angle of minus P, green light is bent at an angle of minus 0, and red light is bent at an angle of minus R (recall that master hologram H1 was inverted during the production of copy 30 hologram H2). Consequently, all wavelengths pass through hologram H2 substantially orthogonally to the plane of lens 1110. As a result, an observer 1116 may view the reconstructed hologram from a viewpoint substantially along a line orthogonal to the plane of hologram H2.

WO 95/14960 2 1 7 7 :~ ~ 8 PCT/US94113639 By coordinating the wavelength-selective diffraction capacity of diffraction grating 1112 with the wavelength-selective diffraction properties of hologram H2, substantially all of the light diffracted by diffraction grating 1112 may be used to illuminate the hologram. Thus, even the use of a relatively inefficient diffraction grating 1 112 produces 5 a relatively bright holographic image. Moreover, the holographic image is not unnecessarily cluttered by spurious white hot which is not diffracted by grating 1112, inasmuch as a substantial amount of this spurious light will be blocked by louvers 1114.
Moreover, by mounting the thin, planar hologram, louvers, and diffraction grating on the surface of a lens which forms a portion of the viewing apparatus, the replay beam 10 used to illuminate the hologram is substantially exclusively limited to the collimated light from source 1108; that is, spurious noncollimated light is prevented from striking the rear surface (right-hand side in Figure 11) of hologram H2.
Altern~tive Li~ht Control Film [~ o~ t~
Referring now to Figure 13, in accordance with an alternative embodiment of 15 ewing assembly 1102, a light control film 1310 may be suitably employed in lieu of louvers 1114.
Moreparticularly, lightcontrolfilm 1310suitablycomprisesathin, lld~ Jdl~"tfilm laminate made from a plurality of thin planar sheets sandwiched together, as described in greater detail below. In the embodiments set forth in Figure 14, light control film (LCF) 20 1310 comprises three laminated sheets, namely a front sheet 1402, a core sheet, 1404, and a back sheet 1406. Each of the foregoing sheets comprises a thin, I~d~ a,~"l film, with a series of thin, parallel, opaque lines extending across the entire surface of the film.
To illustrate the optical properties of LCF 1310, these sheets are shown in cross-sections;
for clarity, a front view of an exemplary sheet 1402 is shown in Figure 15, with the 25 thickness of the opaque lines ~xd~ ldled for illustration purposes. Respective opaque lines 1402A, 1402'3, 1402C, etc. shown in Figure 15 may be seen in cross-section in Figure 14. Respective sheets 1404 and 1406 are suitably similar or identical to sheet 1 402.
With continued referenceto Figure 14, LCF 1310 isconvenientlyviewed asa light 30 filter, such that the duty cycle of a constituent sheet (e.g., sheet 1402) is a function of the width W1 of an exemplary opaque line (e.g., line 1402A relative to the width W2 of the distance between consecutive lines). I the embodiments shown in Figure 14, each of the ~9-wo 95114960 2 1 ~ 7 ~ 5 ~ PCTIIsS94ll3639 respective sheets 1402-1406 suitably exhibit an opaque duty cycle on the order of 50%, i.e., W1 is d5J5~1U~illldl~ly equal to W2.
The quality of grating 112 may be expressed in terms of its ability to selectively diffract incoming white like 1408. As discussed above in connection with Figure 11, s diffraction grating 1112 diffracts light at an angle as a function of wave length. For example, red light rays 1410 are diffracted at a relatively steep angle from the horizontal, green light 1412 is diffracted at less than red light, and blue light 1414 is diffracted at a relatively small angle from the horizontal.
Diffraction gratings are typically not 100% efficient. Thus, a ~u~1sid~l dule amount 0 of undiffracted light inevitably passes through grating 112. In the context of the present invention, undiffracted light which passes through grating 1112 is referred to herein as zero order light 14-16, whereas the diffracted light (e.g., rays 1410-1416) are referred to as first order diffracted light.
To facilitate the reconstruction of a sharp, high contract, hologram, LCF 1310 is ~s suitably configured to block zero order light 1416 such that it is nût viewed by viewed 1116, and at the same time to pass the diffracted first order light therethrough. As discussed above in conjunction with Figure 11, the first order light which passes through LCF 1310, will be inversely diffracted by the hologram and directed horizontally to be viewed by the observer.
In accordance with a first embodiment of LCF 1310 shown in Figure 14, front sheet 1402 îs suitably dispDsed with respect to back sheet 14û6 such that their respective opaque and ~Idn~d,~"I lines are aligned. Core sheet 1404, on the other hand, is suitably disposed such that its opaque lines 1404A, 1404B, etc. are in registration with the ~Sdl ,~.a,~l~t portions of front sheet 1402 and back sheet 1406, while the opaque portions 2s of core sheet 1404 are disposed in registration with the transparent portions of front sheet 1402 and back sheet 1406. Consequently, most of the zero order light which passes through grating 1112 will be blocked by LCF 1310. However, the present inventor has observed that a small amount of zero order light, as shown for example at ray 1416A, inevitably passes through LCF 131 û. The zero order light 141 6A which passes through 30 LCF 1310 may be attributed to several factors, including: vertical misalignment of one or more of sheets 1402-1406; flaws or imperfections in the opacity, width W1, parallelism, or position of one or more of the opaque lines ~u",5,,ising one or more of sheets 1402-_5~

WO 951149C0 2 1 7 7 ~ 5 8 PCT/US94/13639 1406; refraction of light through LCF 1310, and diffraction of zero order light around oneor more of the edges of the opaque lines ~u~luliSirlg LCF 1310.
Accordingly, while the ~ o~ , set forth in Figure 14 produces acceptable results, alternate configurations of light control film may also be employed in the context 5 of the present invention.
Referring now to Figure 16, an alternate embodiment of light control film 1610 suitably comprises a front sheet 1602, a core sheet 1604, and a back sheet 1606, wherein the relative dimensions of the various opaque lines ~u~,u~i~illg sheets 1602-1606 are suitably manipulated such that opaque lines 1604A, 1604B, etc. "overlap" the edges of 0 the opaque lines ~u"~u,i~ir,g respective front and back sheets 1602 and 1606. The configuration shown on Figure 16 substantially reduces the extent to which zero order light may diffract around the opaque lines embodied in LCF 1610. Alternatively, the plurality of core sheets having substantially thinner (dimension W1 ) opaque lines may be employed, with the opaque lines of the core sheets being staggered in various s configurations to preclude the passage of zero order light through the light control film.
However, the usefulness of such ~ "~odi~ are limited to the extent they also tend to block the passage of first order light therethrough, for example, narrowing the band width of first order light which can pass through the various layers comprising the light control film.
More particularly and with Illolll~ ly reference to Figure 17, even a relativelysmall overlap 170~ in the width of opaque lines 1704A and 1704B can significantly reduce the amount of first order light which passes through LCF 1710 for certain wave lengths from a first amount defined by pathway 1712 to a second amount defined by pathway 1714.
With continued reference to Figures 14-17, it can be seen that the vertical uplifting of one or both of the front and back sheets tends to block wave lengths at the extreme ends of the band width for which the light control film is designed to pass. It can also be seen that vertical shifting of the core (intermediate) sheets tends to reduce the amount of intermediate wave lengths which pass through the LCF. Ideally, an LCF should be 30 configured to pass all desired first order wave lengths equally well, while blocking substantially all zero order light.

WO 95/14960 2 1 7 7 ~ 5 ~ PCT/US94/13639 Referring now to Figure 18, an alternate LCF embodiment is shown which substantially decouples the zero order blocking cdpability of the LCF from the LCF's cdpacity to pass first order light.
Referring now to Figure 18, an alternative embodiment of an LCF 1810 suitably 5 comprises a front layer 1802, a core layer 1804, and a back layer 1806 In accordance with one aspect of LCF 1810, back layer 1806 may be thought of as a datum, whereupon shifting of front layer 1802 results in color selectivity, and a w~,uol~dillg shift in core layer 1804 provides good zero order blocking.
As shown in Figure 18, substantially all of the zero order light 1416 which passes 0 throughgrating1112willbeblockedbyLCF1810. Inaddition,LCF1810isconfigured to facilitate passage of a desired band width of first order diffracted light therethrough.
The particular dlldl~ ",e:"l of the various sheets ~ul~ g composite LCF 1810 areconveniently described in the context of a preferred embodiment whereby LCF 1811~ is constructed. Accordingly, a detailed methodology for manufacturing LCF 1810 will now 5 be described.
With continued reference to Figure 18, LCF 1810 is suitably manufactured using a sturdy, flat, viewing apparatus of the type discussed above in conjunction with Figure 11, rotated d~ ly 90 such that the viewing screen is substantially horizontal and may thus be viewed by the operator during assembly of LCF 1810. In the 20 context of Figure 18, grating 1112 would thus be oriented horizontally, with respective sheets 1802, 1804, and 1806 assembled with back sheet 1806 on the bottom and fron~
sheet 1802 on top, as described in greater detail below.
As an initial manufacturing step, a protective glass sheet 1816, for example a 3/8"
slab of glass, is suitably laid horizontally on top of the surface of viewing screen 1818 to 25 avoid damage to the viewing screen during assembly of LCF 1810. Thereafter, it may be desirable to place a protective coating over the glass, for example a thin, lldll~j~dl~
polyester, sheet (polyester sheet 1820) to prevent any adhesives used during assembly from contacting glass sheet 1816.
To facilitate handling and installation of laminated LCF 1810, it may be desirable 30 to construct the laminate as a composite, wherein LCF 1810 is sandwiched between respectjve sheets of glass 1822 and 1824. Accordingly, rear sheet 1822 is suitably thoroughly cleaned and plaoed on top of polyester protective sheet 1820. Respective -s2-WO 95114960 2, 7 7 3 5 8 PCIIUS94/13639 glass sheets 1822 and 1824 are suitably on the order of one to five millimeters in thickness, and most preferably in the range of about 2.3 millimeters thick.
As best seen in Figure 18, it is desirable that glass sheet 1822 comprise rectangular dimensions on the order 14 7/16" in height by 7 7/16" wide, and for respective fi!m 5 sheets 1806, 1804, and 1802 to exhibit successively smaller rectilinear dimensions, with glass sheet 1824 having the smallest rectangular dimensions. The various sheets can be stacked on top of one another and conveniently manipulated by the operator during assembly.
With continued reference to Figure 18, the first active layer of the LCF is suitably 0 placed on top of glass sheet 1822. Specifically, back sheet 1806 is disposed on top of glasssheet 1822,with respectofopaquestrips 1806A, 1806B,andthelikerunningfrom left to right as viewed by the operator 1116. In a particularly preferred embodiment, the film comprising respective sheets 1802-1806 is Kodak Accumax 2000 ALI7. In a preferred ~",I,o,li",e,~l, respective sheets 1802-1806 are on the order of 7 mils. thick, and suitably 15 comprised polyester, acetate, or any convenience lld"~.a,~"l material.
In accordance with the further aspect of the present invention, the respective opaque lines ~u~ Jri~ g the various sheets within the laminate are suitably on the order of 12 mils. in width (dimension W1; see Figure 14), with spaces on the order of 11 mils, such that that duty cycle of the various light block films are in the range of ~0% to 60%, 20 and preferably in the range of 50% to 60%. In addition, the emulsin which comprises the opaque stripes may be imbedded within the thickness of the film or, alternatively, may be deposited on the surface of the film at a thickness of ap~,,.,xil"dlely 6 microns.
After positioning film sheet 1806 on top of glass sheet 1822, film sheet 1806 issuitably secured to the glass sheet, for example by wiping a hypodermic needle across the 2s tip of a bottle of Locktite~ Unlocktite 351, or any other suitable general purpose ultraviolet (UV) adhesive.
The adhesive is then wiped onto the underside of two or more corners of film 1806, and a UV light applied to the adhesive region to cure the adhesive, thereby securing film sheet 1806 to glass sheet 1822.
In accordance with the preferred embodiment, a suitably ultraviolet curing lamp comprises a 100 wan UV flood lamp, for example a Spectronics SB 1 OOC hand held UV
lamp.
-s3-WO 9sl14960 ~ ~ 7 ~ 3 5 ~ PCTNS941~3639 Core sheet 1804 is this placed on top of back sheet 1806, with the opaque lines running from left to right. In order to properly position core sheet 1804 on top of back sheet 1806, the operator suitably looks directly downwardly toward the film, such that the operators line of vision is substantially orthogonal to the film plane. Sheet 1804 is 5 then manipulated until the opaque lines of sheet 1804 are in ~ ,dliu" with the opaque lines of sheet 1806, such that sheet 1806 is essentially hidden behind sheet 1804. Once the two sheets are exactly aligned, any air between the sheets is suitably wiped out to provide for intimate sliding contact between the two film sheets. Through the use of small portable",i.,u~up~,forexample,aTasco30XmicroscopeavailablefromtheH&R
0 catalogue, core film 1804 is suitably slid toward the operator slightly (downwardly in Figure 18), so that the opaque lines of sheet 1804 overlap the opaque lines of sheet 1806 by app,u;~i",dl~ly 50%. Though the use of the drur~",~:"lioned microscopes, this may be accomplished visually with relative ease. By using the ~ u~up~s at the four corners of the composite, it is also relatively easy to ensure that the opaque lines of sheet 1804 15 are substantially parallel to the opaque lines of sheet 1806 throughout the entire surface of the sheet. In this position, an exemplary edge 1826 of an arbitrary opaque line of sheet 1804 is suitably disposed d~Jpluxillldl~:ly one half way between respective edges 1828 and 1830 of an adjacent opaque line 1806B on sheet 1806.
Core sheet 1804 is then temporarily taped in place, for example by placing two 20 pieces of tape at the bottom edge of sheet 1804, temporarily securing sheet 1804 to film sheet 1806 and glass sheet 1822.
Front sheet 1802 is then placed on top of core sheet 1804, such that the variousopaque lines 1802A, 18û2B, etc. are aligned with the opaque regions defined by the overlapping opaque lines of sheets 1804 and 1806. Sheet 1802 is then slowly urged 25 slightly toward the operator (downwardly in Figure 18) until all zero order light is completely blocked. This will be apparent to the operator in that all zero order light which passes through grating 112 and the various components set forth in Figure 18 is totally blocked. To confirm that the zero order light is essentially totally blocked, the operator may turn the brightness level in the bulb disposed within the viewing apparatus 30 to a maximum level.
Specifically, zero order light will be totally blocked when edge 1832 of opaque stripe1802Aisslightlyaboveedge18340fanopaquestripe1826foreachofthevarious opaque stripes ~u",u,isi~g respective sheets 1802 and 1804. The degree of overlap WO 95/14960 2 1 7 7 3 ~ ~ PCTNS94/13639 between respective edges 1832 and respective edges 1834 may be conveniently defined as dimension L. In accordance with the preferred embodiment of the present invention, dimension L should be as small as possible while insuring complete blockage of zero order light.
As an additional step in ~u,~ri,ll, ,g that sheet 1802 is properly positioned, the operator may lean forward over the assembly, such that he looks downwardiy and rearwardly at the assembly, for example from position 1814B. From position 1814B, the operator can observe any "backlight" which may shine through LCF composite 1810.While the backlight will typically be substantially lower in intensity than the zero order 0 lighl, it is nonetheless desirable to block as much backlight as possible; this may be accompl ished by minimizing dimension L wh ile insuring complete biockage of zero order light.
Front layer 1802 is then secured to layer 1804, for example by applying a few pieces of adhesive tape to fasten layer 1802 to layer 1804.
s Having confirmed that all zero order light is blocked, one or both of sheets 1802 and 1804 may be moved slightly to achieve optimum color balance. In this regard, the operator may step away from the assembly, and/or bend down slightly, such that he observes the assembly from position 1814A such that he is "looking up" the tunnel defined by the series of opaque lines. In the configuration set forth in Figure 18, it is 20 possible to observe what appears to be a comet, which the present inventor believes to be a scattered image of the filament of the source light within the viewing apparatus.
The operator then urges core layer 1804 toward him (downwardly in Figure 18), while maintainin~ sheet 1802 essentially stationary. This manipulation effectively increases dimension L, further insuring total zero order blockage. Alternatively, front 2s sheet 1802 may be urged upwardly in Figure 18, either in addition to or in lieu of urging layer 1804 downwardly, to effect a slight increase in dimension L without increasing the amount of backlight observed from position 1814B.
An exemplary hologram may then be placed on top of the assembly to insure proper color and zero order blockage. To the extent that the operator desires to fine tune 30 the color spectrum passing through LCF 1810, he may manipulate core layer 1804 upwards or downwards slightly, while insuring complete zero order blockage, to obtain desired variations in color.

WO 95/14960 ~ 1 7 7 ~ 5 8 PCT/US94/13639 Once the three layers ~ illg LCF 1810 are properly positioned, they are secured to one another at their corners through the aforementioned UV adhesive. Glass plate 1824 is then placed on the assembly, and the enlarge planar pressing tool is placed on the entire assembly to expel air from between the various laminates in the assembly.
5 A bead of UV cement is then applied around the perimeter of the assembly, leaving a small gap in the perimeter bead. A hypodermic needle is then inserted into the gap, which hypodermic needle suitably comprises a 303 stainless steel, 25 gauge, thin wall tube.
The peripheral, adhesive bead is then completed, essentially completing the 0 perimeter seal with the hypodermic needle in place. A vacuum lead, for example a teflon hose, is then secured to the distal end of the hypodermic needle, and a vacuum, on the order of 25 inches of mercury pressure, is applied to the hypodermic. This insures that any residual air within the laminated assembly is withdrawn through the hypodermic.
When all air is withdrawn from the assembly, a hot lamp or blow torch may be 15 used to soften the hypodermic, such that the hypodermic collapses upon itself, creating an airtight region inside the adhesive bead. During the heating process, the hypodermic needle is suitably squeezed with needle-nosed pliers to flatten it out and may be advantageously gripped ~vith channel grip pliers to insure a strong, light, mechanical airtight seal. The end of the hypodermic needle is then folded back into the adhesive 20 bead, and the entire perimeter of the assembly is taped to insure a stable, air tight, mechanically sound composite laminate structure.
Modifications and ~nhancements When a hologram (H2), produced in accordance with the present invention, is mounted on box 1102, a three~li",el-siol-al ~ "I~Lion of the object may be seen,2s affording the viewer full parallax and perspectives from all viewpoints. The present inventor has further determined that the hologram may be removed from the viewbox, inverted, and placed back on the viewbox. The inverted hologram contains all of the same data as the noninverted view of the same hologram, except that the observer is looking at the hologram from the opposite direction; that is, points on the hologram 3C which previously were furthest away from the observer are no~ closest to the observer, and vice versa. This feature may be particularly useful to physicians when mapping out a proposed surgical procedure, for example, by allowing the physician to assess the various pros and cons of operating on a body part from one direction or the other.
-s6-WO 95/14960 2 1 7 7 3 ~ 8 PCT/US94/13639 The present inventor has also determined that two or more holograms may be simultaneously viewed on the same viewbox, simply by pldcing one hologram on top of the other hologram. This may be particularly significant in circumstances where, for example, the first hologram comprises a body part (e.g, hip) which is to be replaced, and 5 the second hologram comprises the prosthetic replacement device. The physician may thus view the proposed device in proper context i.e., as the device would be implanted in the three~;""~ iv"dl space within the patient.
Moreover, it may be advantageous to overlay a hologram of a coordinate grid, e.g, a three-dimensional coordinate grid, with the hologram which is the subject of inspection.
0 In this context, a suitable coordinate grid may simply comprise a hologram of one or more rulers or other measuring devices having spatial indicia encoded thereon. Alternatively, the coordinate grid may simply comprise a series of intersecting lines or, alternatively, a matrix of dots or other visual markings spaced apart in any convenient manner, for example linearly, logarithmically, and the like. In this way, three-dimensional distances 5 may be easily computed by counting the coordinate markings, particularly if the coordinate grid is of the same scale or of a convenient multiple of the dimensional scale ~vr~,u~ g the hologram.
The present inventor has also observed that very faint patterns of light and dark rings are occasionally visible when viewing a hologram in accordance with the present 20 invention. More particularly, these rings appear to be a great distance behind the hologram when viewed. The present inventor theorizes that these rings constitute an inL~ lv~;la~ which results from taking a llhologramll of diffusing diffuser 472 along with each data slice. To overcome this problem, diffuser 472 may be shifted slightiy (e.g., ten millimeters) within its own plane after each data slice is recorded. In this way, the image 25 ~vll~Jol~d;l,g to each data slice is still projected onto film 319 as described herein, yet a slightly different portion of diffuser 472 is projected for each data slice, thereby avoiding projection the same pattern attributable to diffuser 472 for each data slice.
It is also possible to add textual or graphical materiaL for example to one or more data slices, thus permitting the resulting hologram of the data set to reflect this textual or 30 graphic material. Such material may comprise identification data (e.g., patient name, model or serial number of the object being recorded), or may comprise pure graphical information (arrows, symbol and the like).

WO 95/149~0 2 t 7 ~ ~ ~ 8 PCT/US94/13639 In this regard, it is interesting to note that text which is viewed in the orthoscopic view will be inverted in the pseudoscopic view of the same hologram; that is, if text appears right-side up in the orthoscopic view, it will appear upside down in theps~dc\scopic view. Thus, to the extent it is desirable to utilize text within a hologram, it may be advantageous to insert the same text right-side up at the top of the hologram and upside down at the bottom of the hologram, so that text may be properly observed regardless of whether the hologram is viewed in the orthoscopic or pseudoscopic construction .
Moreover,textwhichisinthefilmplanewillgenerallyappearsharpduringreplay, 0 whereas text disposed out of the film plane, I.e., along axis A in Figure 1, generally appears less sharp. This may be advantageous in accordance with one aspect of the invention, inasmuch as "out of film plane" text would be legible when viewed on a Voxbox, but illegible without a Voxbox. In the context of holograms used for medical diagnosis, it may thus be desirable to place confidential patient information, for example a patient's name, condition, and the like, out of the film plane so that such information may be most easily viewed by proper personnel with the aid of a Voxbox, thereby ensuring patient confidentiality.
In addition to textual and graphical material, it may be desirable to include additional images, for example a portion of the image ~o",p, i,i"g a particular hologram, 20 or image data from other holograms, onto a master hologram. For example, consider a master hologram of a fractured bone .u" ,~., i,i"~5 one hundred or more sl ices. For the few slices which comprise the key information, it may be desirable to separately display this data spaced apart from the overall hologram, yet adjacent to the hologram and at the proper depth with respect to the hologram.
2s As briefly discussed above, wherein, a hologram produced in accordance with the present invention is viewed on a Voxbox or other suitable viewing device, the orthoscopic view of the hologram may be observed when the hologram is in a firstposition, and the p5F~Ilrlr)crr)pjc view may be observed when the hologram is rotated about its horizontal axis. Since it may be difficult to determine whether a particular 30 orientation of the holographic film corresponds to the orthoscopic or rs~ lr~s~rjc view with the naked eye, it may be desirable to place convenient indicia on the holographic film to inform the viewer as to which view of the hologram may be observed when the holographic film is placed on a viewing apparatus. For example, it may be desirable to -~8-WO95/14960 2 ~ 77~ PCT/US94113639 place a notch or other physical indicium on the film, for example in the upper right hand corner of the orthoscopic view. Alternatively, a small textual graphical or color coded scheme may be employed by placing appropriate indicia at a corner, along an edge, or at any convenient position on a holographic fiim or on any border, frame, or packaging 5 therefor.
In accordance with another aspect of the present invention, it may be efficient to window onIy a portion of the data slices and nonetheless achieve satisfactory contrast and shading. For example, for a 1ûO slice data set, it may be possible to manually window every tenth data slice, for example, and through the use of computerized interpolation 10 techniques, automatically window the interstitial data slices.
In accordance with a further aspect of the present invention, it is possible to select the film plane among the various data slice planes ~ur~uliSillg the data set. More particularly, each data slice within a data set occupies its own unique plane. In accordance with the preferred ~ bodilll~ of the present invention, track assembly 334 15 is moved forward or backward such that the data slice which is centered within the volume of the data set corresponds to the data slice centered within the length of travel of track assembly 334. The relative position of imaging assembly 328 and film 319 may be varied, however, so that the plane of film 319 is located nearer to one end of the data set or the other, as desired. The resulting hologram H2 will thus appear to have a greater 20 or lesser portion of the holographic image projected into or out of the screen upon which the hologram is observed, depending on the position that the film plane has been selected to cut through the data set.
In accordance with a further aspect of the invention, a plurality of different holograms may be displayed on a single sheet. For example, a hologram of a body part 25 before surgery may be displayed on the upper portion of a film, with the lower portion of the film being divided into two quadrants, one containing a hologram of the same body part after surgery from a first perspective, and the other portion containing a view of the same body part after surgery from another perspective. These and other holographic compositions may be suitably employed to facilitate efficient diagnostic analysis.
In accordance with a further aspect of the present invention, the entire beam path is advantageously enclosed within black tubing or black boxes, as appropriate. This minimizes the presence of undesirable reflections. Moreover, the entire process of maker master and copy holograms is advantageously carried out in a room or other enclosure which is devoid of spurious light which could contact any film surface. Alternatively, the path travelled by any of the beams in the context of the present invention may be replaced with fiber optic cable. By proper seledion of the fiber optic cable, the polarization and Transverse Cle.~lu",dE;"etic Mode (TEM) of the light travelling through s the cable is preserved. Use of fiber optic cable permits the system to be highly ~UI 1 Ipl ~d, and further permits the e~ imination of many of the components of the system entirely (e.&, mirrors). Finally, fiber optic cables may be used to compensate for a differential path length between the reference beam and the object beam. Specifically, to the extent the path travelled by one of the beams differs from the other, a 0 p,ed~ "" ,t:.l Iength of fiber optic cable may be employed in the path of the beam travelling the shorter length to ~U~ dl~ for this difference in length and, hence, render the two paths equal.
Returning briefly to the rc~ cr~pic construction shown in Figure 10B, it may be desirable under certain circumstances to replay the master hologram and view the 5 three-dimensional image in free space. For example, it may be beneficial to a surgeon to rehearse a surgical technique on a particular body part prior to performing the surgery.
In this regard, a 6 space digitizer, for example a BirdlM part no. 60û102-A manufactured by the Ascension Technology Corporation of Burlington, Vermont, may be advantageously employed in the context of a rS~r~os~lric construction.
More particularly, a 6 space digitizer is capable of being manipulated in free space, and reporting its position to a computer, much like a conventional computer mouse reports two-dimensional position data to its computer. By moving through the holographic space, size and other dimensional data may be unambiguously obtained with respect to the hologram.
With continued reference to Figure 10B, it may also be desirable to replay a hologram partially or wholly out of its film plane, for example in free space, in order to perform various diagnostic and experimental tasks. For example, it may be advantageous to project a holographic display of a portion of human anatomical structure, for example an injured hip, and to physically place into the holographic space a prosthetic device intended to replace the hip or other anatomical element. In this way, the "fit" of the prosthetic device may be ascertained and any dp~Jruplid~ corrections made to theprosthetic device prior to implanting the device.
~o-2 ~ 77358 WO 951~4960 PCT/US94/13639 .
In addition, it may be desirable to replay a hologram in free space and place a diffusing screen or oth~r l,a"~-a,~:,lI or opaque structure into the holographic space to permit interaction with the subject matter of the hologram for various ~x!J~,i",~ dl and diagnostic purposes.
5 Although the invention has been described herein on con junction with the appended drawings, those skilled in the art will appreciate that the scope of the invention is not so limited. For example, while the view box has been described as being rectangular, those skilled in the art will appreciate that any suitably mechanical configuration which conveniently houses the various components of the viewing 0 apparatus will suffice. Moreover, although the camera and copy assemblies are illustrated as separate systems, they may suitably be combined into a single system.
These and other modifications in the selection, design, and al,dl,;Se",~"I of the various ~ ,uol~ s and steps discussed herein may be made without departing from the spirit of the invention as set forth in the appended claims.

Claims (18)

CLAIMS:

1. A laminated light control film assembly for use in a hologram viewing apparatus, comprising:
a back film sheet having a first series of alternating opaque and transparent parallel lines;
a core film sheet disposed on top of said back sheet, said core sheet having a second series of alternating opaque and transparent parallel lines; and a front sheet disposed on top of said core sheet such that said core sheet is interposed between said front sheet and said back sheet, said front sheet having a third series of alternating transparent and opaque parallel lines:
wherein said core sheet, said back sheet, and said front sheet are positioned with respect to one another to substantially block first order light from passing through the assembly, while facilitating passage of a predeterminedband width of first order light therethrough.

2. The assembly of claim 1, wherein for at least one of said series of lines, the width of each of said opaque lines is substantially equal to the width of each of said transparent lines.

3. The assembly of claim 1, wherein said back, core, and front sheets are configured such that shifting of said front sheet with respect to said core sheet and said back sheet along a direction orthogonal to said parallel lines controls the color selectivity of said assembly.

4. The assembly of claim 1, wherein said back, said core, and said front sheet are arranged with respect to one another such that a shift of said front sheet with respect to said core sheet and said back sheet produces a corresponding change in the band width of said predetermined band width of first order light which passes through said assembly.

5. The assembly of claim 1, wherein said back, said core, and said front sheets are configured such that a small movement of said core sheet with respect to said back sheet in a direction substantially orthogonal to said parallel lines controls the degree of blockage of zero order light through said assembly

6. The assembly of claim 1, wherein said first, said second, and said third series of lines are configured such that small movements of said front sheet with respect to the other sheets along a direction orthogonal to said lines controls the color selectivity of said assembly in a manner which is substantially decoupled from the ability of said assembly to block the passage of zero order light.

7. The assembly of claim 1, further comprising a light source disposed to illuminate said assembly, and a diffraction grating interposed between said light source and said assembly.

8. A laminated light control film assembly, comprising:
a back film sheet having a first series of alternating opaque and transparent parallel lines extending across the surface thereof;
a front sheet having a third series of alternating transparent and opaque lines extending across the surface thereof; and a core film sheet disposed intermediate said back film sheet and said front sheet, said core sheet having a second series of alternating opaque and transparent lines extending across the surface thereof;
wherein said first, second, and third series of lines are arranged with respect to one another such that light traveling in a direction substantially orthogonal to the plane of the assembly is substantially impeded from passing through said assembly, and further wherein a predetermined band width of light is configured to pass through said assembly, said predetermined band width defining a predetermined angle of incidence with respect to the plane of said assembly.

9. The assembly of claim 8, wherein each of said opaque lines of said first series are of substantially the same width, each of said opaque said linesof said second series are of substantially the same width, and each of said opaque lines of said third series are approximately the same width.

10. The assembly of claim 9, wherein the duty cycle of at least one of said core, said front, and said back sheets is approximately fifty percent (50%).

11. The assembly of claim 8, wherein the opaque lines of at least one of said first, second, and third series are suitably on the order of 12 mils in width, with corresponding spaces on the order of 11 mils in width.

12. The assembly of claim 11, wherein the duty cycle of each of said front, core, and back sheets is in the range of forty (40%) to sixty (60%) percent.

13. The assembly of claim 8, wherein each of said front, said core, and said back sheets are on the order of 7 mils thick.

14. The assembly of claim 8, wherein each of said front, said back, and said core sheets comprise one of polyester and acetate.

15. A method of assembling a composite light control film laminate for use in conjunction with a light source and a diffraction grating interposed between said light source and said laminate useful in viewing holograms, comprising the steps of:
providing a first light control film sheet comprising a first series of alternating opaque and transparent lines extending across the surface of said first sheet:
providing a second sheet on top of said first sheet, said second sheet comprising a second series of alternating opaques and transparent lines extending across the surface of said second sheet;
manipulating said second sheet with respect to said first sheet such that said opaque lines of said first series overlap said opaque lines of said second series by approximately fifty percent (50%);
disposing a third sheet, having a third series of alternating opaque and transparent lines, on top of said second sheet;
manipulating said third sheet until substantially all zero order light is blocked by the combination of said first, said second, and said third sheets; and thereafter manipulating one or both of said second and third sheets, while maintaining parallelism among said first, second, and third series of lines, to achieve predetermined wavelength selectivity of the first order light which passes through said laminate.

16. The method of claim 15, further comprising the step of urging said second layer in a direction substantially orthogonal to said second series of opaque lines, while maintaining said third sheet essentially stationary, to maximize the blockage of zero order light.

17. The method of claim 15, further comprising the step of removing substantially all of the air from between said first and said second sheets and from between said second and third sheets.

18. The method of claim 15, further comprising the step of immovably securing said first, second, and third sheets together once predetermined color selectivity and optimum zero order blockage are achieved.