CA2090483A1

CA2090483A1 - Fabrication of multifunctional holographic optical elements and application in photometers

Info

Publication number: CA2090483A1
Application number: CA002090483A
Authority: CA
Inventors: Gerald E. Cohn; Richard A. Domanik; Tung H. Jeong; Edward Wesley
Original assignee: Individual
Current assignee: Abbott Laboratories
Priority date: 1990-10-03
Filing date: 1991-10-03
Publication date: 1992-04-04
Also published as: EP0551430A1; WO1992006361A1; EP0551430A4; JPH05507355A

Abstract

The application of one or more multifunctional holographic optical elements (HOE's) (40, 16) to a photometric apparatus, and a spectrophotometer in particular, is disclosed. Fabrication methods for HOE's especially useful in the foregoing application result in holograms which perform several classical optical (i. e., light gathering and steering) functions. The HOE's so fabricated are useful in a detector mode (16) (i.e., to process light from an illuminated sample for analysis of some portion of its spectrum); in a source mode (40) (i.e., processing light from a source (51) to a focus on a sample); and a combination of source and detector modes.

Description

~ 2090a~83 `-` `
v~ p W O 92/06361 PC~r/US91/07318 FABRICATI OF MULTIFUNCTIONAL HOLOGRAPHIC OPTICAL
ELE~ r NTS AND APPLICATION IN PHOTOMETERS

FIELD OF THE INVENTION
The present invention generally relates to the fabrication and use of holographic optical elements, and is particularly related to the application of holographic -~
optical elements to photometers. More specifically, the present invention relates to multifunctional holographic optical elements made for use in an improved spectrophotometer for colorimetric analysis of light transmissive samples.

BACKGROUND OF THE INVENTION
The present invention generally began as an effort to apply holographic optical element (HOE) technology to produce an improved spectrophotometer.
Spectrophotometers are well known, generally comprising:
a light source for illuminating a sample; a prism or grating device for dispersing light from the sample into a spectrum; and detectors, such as photomultipliers or photodiodes, for generating a signal related to a portion of the sample spectrum. Data processing means then analyze the signal(s) for content of the sample, such as a colormetric reading which can be correlated to one or more sample constituents. An absorption spectrophotometer of the foregoing type is described in V.S. Pat. No. 4,195,932, and commercialized by Abbott Laboratories under the name of "QUANTUM".
The spectrophotometer of the '932 patent uses classical" optical elements for focusing light from the light source onto the sample and for processing the light from the illuminated sample into a spectrum for analysis.
That is, the beam-shaping and modifying optics include lenses, dichroic mirrors, interference filters and beam-splitters. While extremely satisfactory results are achievable through the use of classical optics in a spectrophotometer, there are disadvantages attendant to the SU8STITUTF SHE~
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~ 2 use of the same. For ex~ample, the optical elements in the light train have to bef precisely oriented in the apparatus, requiring precision in assembly of the photometer. Each optical element must also be relatively free from defect, increasing cost, with the various elements required thereby adding to the overall expense of the apparatus.
The optical elements also take up a certain amount of room, dictated in part by the size of the elements and their relative focal distances. A light source of sufficient intensity to make up for light losses in the optical train must also be used. This generally entails use of a higher power (intensity) light source, which then must be adequately shielded, and even cooled, so as to not adversely affect the sample or the electrical and optical components.
Holograms have been used in photometric devices as part of a beam processing system. Holograms are well known, constituting a specialized recording of an interfexence pattern formed when coherént light from a laser, for instance, is divided into two separate beams--object and reference beams--which are then recombined at a holographic plate or film. The most significant property of a hologram is its ability to reproduce in three dimensions the image of the object which was recorded, when the hologram is illuminated by a light beam having the same wavelength, general shape and direction as the original reference ~eam.
In general, holograms used in photometric devices have been simply applied as a grating to disperse light from the sample into a spectrum for analysis; classical optical elements are used for the remainder of the system.
Spectrophotometer using holograms in this fashion are shown in U.S. Pats. Nos. 4,211,486, 4,540,282 and 4,687,329, for example.
Holograms can be designed to perform the same light-proc~ssing functions as classical optical components, however, in~luding some operations not readily handled by S~3~ ~E~

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WO92/06~1 ~ P~T/US91/07318 standard optics. For instance, a lens, mirror, prism or other optical element in the holographically recorded scene will act in the hologram exactly as the original element:
lenses will focus or diverge, mirrors reflect, etc. Since holograms can be made which will reproduce an entire monochromatic output beam from an optical system, a single hologram can recreate the beam which would emerge from a series of classical beam-processing components. The hologram can then replace all of these classical optical components. Such a hologram is referred to in general, and herein, as a holographic optical element or HOE.
AS applied to a spectrophotometer, for instance, HOE's offer potential benefits over classical optical systems. The functions of some or all conventional optical components can be incorporated into one or more HOE's, reducing cost, parts, and inventory. Assembly time, particularly with regard to alignment, is reduced, since a flat-plate HOE, for example, is simpler to mount. The overall si~e and weight of the spectrophotometer are also significantly reduced. HOE's can be made in high-volume production lots through simple replication from a master hologram. This results in lower cost and tighter tolerances than are practical with multiple conventional optical components which are manufactured individually.
HOE's may further increase the optical efficiency of the system, enabling the use of a much lower intensity, and therefore lower power, light source. HOE's can also be made which perform optical functions which are difficult to achieve or implement using conventional optical components, such as providing focusing elements with extremely short focal lengths and relatively large diameters.

SUMMARY OF THE INVENTION
The present invention resides, in part, in the application of one or more multifunctional holographic optical elements ( HOE ' s ) to a photometric apparatus, and a spectrophotometer in particular. The present invention SUBST~TUTE SH~E~

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The multif~nctional HOE referred to herein can generally be considered to be a hologram which performs s0veral classical optical functions (i.e., light gathering and steering). For instance, a HOE of the type in point mzy combine the functions of a collector, a dispersing element and a focussing element in a single hologram. It is therefore to be distinguished from a hologram used simply as a diffraction grating.
More specifically, the present invention provides some basic implementations in spectrometric apparatuses where a HOE is used: in a detector mode (i.e., to process light from an illuminated sample for analysis of some portion of its spectrum); in a source mode (i.e., processing light from a source to a focus on a sample); and a combination of source and detector modes. Two fabrication methods, or arrangements, have been employed to advantage. In both, holographic construction is employed in generally the same fashion as for a standard two-beam hologram: two mutually coherent laser beams meet at a holographic recording surface (plate) and interfere to form the hologram. Either transmission or reflection HOE's may be fabricated and employed according to the present invention, although transmission HOE's have been the focus of the efforts leading to the present invention.
One application and fabrication method developed in accordance with the present invention employs a single detector HOE to collect, disperse and selectively focus light from an illuminated sample onto detectors, as for the analysis of a selected peak and sideband wavelength in bichromatic photometry. Classical optics can be used to focus light from a white-light lamp to a vertical line segment at the axis of a cylindrical sample tube, or cuvette. In one detector HOE fabrication techni~ue, an object beam path contains two focusing elements in the form of a cylinder lens mounted horizontally to provide at least .

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partial vertical beam collimation and a second cylinder lens mounted with its axis oriented vertically for horizontal beam convergence. A collimator and cylinder lens combination could also be used to the same end. The resulting object beam is a line segment which is brought to a focus as an image in front of the holographic recording medium surface. The reference beam is brought to a converging focus, as by the use of a low F-number positive `
lens, at a point beyond the recording surface. For a transmission hologram, that point for the reference beam would be behind the recording surface.
The HOE which results form the foregoing fabrication method approximates the playback beam source 7', in its spectrophotometer application; a vertical line segment focus for the HOE is used in view of the application of the HOE in spectroscopy of an elongated light-transmissive sample. With this detector HOE located with its line segment focus generally coincident with that of the playbac~ beam, i.e., coaxial with the axis of the illuminated sample tube, the output from the detector HOE
will be a generally continuous horizontal spectrum having a relatively short vertical height at a detector position.
Each generally monochromatic segment in the output is the playback real image from the reversed reference beam at that wavelen~th.
Another implementation in accordance with the present invention results in a source HOE particularly useful in focusing light from a source, e.g., a lamp, onto a sample to illuminate the sample. A HOE fabrication technique is used in making the source HOE which is similar to that just described with regard to the detector HOE, except that two different wavelength lasers are used in making the final HOE for bichromatic spectroscopy. In one variant, separate flat plate HOE's are fabricated using the approximate desired peak and sideband wavelengths, respectively. These two HOE's are then physically combined so that the respective line segments (again in view of the , SvBsT1TlJ~E SHE~

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W092/06~ PCTJUSgl/07318 elongated light-transmiss~ive sample) produced by each at playbac~ substantially combine at a coaxial and congruent output line focus. I~;~` another variant, a single holographic plate is us~ed with two different exposures at the preselected wavel'engths.
Applying the source HOE so fabricated in a spectrophotometric apparatus, the source HOE is placed so that its output line focus on playback substantially coincides with the axis of the sample tube being illuminated.
The foregoing detector and source HOE ' s can be combined in a single apparatus. Most classical light processing elements formerly used in a spectrophotometer, for example, and the beam-shaping lenses in particular, can thereby be eliminated. The simplicity of the design and construction of such a spectrophotometer obviously result in substantial economies in scale, assembly and cost, particularly when batch replication of the HOE ' s is used.
More generally, the pre~ent invention provides an improved photometer having a source of multiwavelength electromagnetic radiation (e.g., white light) and some means for focusing that radiation into a sample illumination beam. A sample to be examined is mounted for irradiation (illumination) by the foregoing source beam.
A multifunctional HOE is positioned to receive subsequent radiation from the irradiated sample, with the HOE dispersing that subsequent radiation from the sample, into a set of individually focused substantially monochromatic regions. A detector is located to intercept at least one such region, with the detector generating a signal derived from the radiation impinging thereon. That signal i5 then analyzed for an analysis of the sample.
The foregoing HOE, used as a detector HOE in a photometer for analysis of an elongated liquid sample, preferably has an input image in the form of a focused line segment at a predetermined distance from the HOE. The detector HOE is positioned to receive subsequent radiation SU8STIT~ EE~ ~

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A HOE fabricated in accordance with one aspect of the invention and as applied to an elongated sample (e.g., a liquid-containing test tube) has an object beam comprising a beam to provide at least partial collimation along a first axis and through a second means for focusing the light beam to provide substantial beam convergence along a second axis which is perpendicular to the first axis. The first and second means for focusing collectively yield a focused line segment along the second axis in front of a holographic recording medium surface. The reference beam converges to a focus beyond the reco~ding medium surface.
The HOE so fabricated can have the reference beam converging to a focus behind the recording medium surface to form a transmission hologram, or converging to a focus in front of the recording medium surface to form a reflection hologram.
One fabrication technique for such a detector HOE
utilizes focusing means in the form of a cylinder lens having an axis and a planar face, with the planar face mounted normal to the light beam to provide the noted at least partial vertical beam collimation. A second cylinder lens is also mounted normal to the light beam, having its axis perpendicular relative to the first cylinder lens axis for horizontal beam convergence.
The noted at least partial vertical beam collimation is predetermined to match the vertical expansion of the ~eam from the lamp used in this HOE
spectrophotometer application. The object and reference beams each have a respective central axis impinging on the recording medium surface at an angle to a recording medium surface normal, with the beam axes making a mutual angle at recombination that yields a fringe spacing suitable for recording and adequate to provide sufficient wavelength SUE3STITU~E SHEET

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WO92/06361 ` PCT/US91/0731 dispersion at play~ack such that the detector HOE, when mounted with its object line focus generally coincident wiith that of a playba~ beam, disperses light from the sample into a spectrum having a small vertical height at a detector position.
In a specific application of the foregoing detector H~E in a spectrophotometer, the invention comprises a source of white light passed through a first cylinder lens mounted to focus at least a portion of the white light to a source line focus. A light-transmissive sample to be examined is contained in a transparent tubular container, i.e., a cuve~te. A sample holder positions the sample at the source line focus such that light from the source line focus illuminates and passes through the sample. The source line focus is substantially coaxial with an axis of symmetry of the sample (the cuvette axis).
The detector HOE is positioned to receive light transmitted through the sample. For instance, this particular H~E may be a transmission HOE fabricated in the foregoing manner. A detector for detecting at least one substantially monochromatic portion of this spectrum is located at a detector position, and generates a signal derived from the light impinging thereon which is then analyzed to obtain an analysis of the sample.
A very low power light source may be used with such a spectrophotometer. A 1.5 watt light source has been used to advantage, for example. Furthermore, the spectrophotometer can be housed in a casing having the light source, the first cylinder lens, a cuvette holder, the detector HOE and photodiodes used as the detectors. A
first light-blocking baffle between the light source and the first cylinder lens blocks stray light from the light source. A second light-blocking baffle between the cuvette holder and the detector HOE blocks stray light from the ;
illuminated sample, with a mask or masks used with the photodiodes to eliminate light other than said respective SU13~ 3TE SHE~T ~
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Another aspect of the invention is in a photometer utilizing a multifunction HOE to focus a beam ~or illumination of a sample, i.e., a source HOE. Such an apparatus comprises a source of multiwavelength electromagnetic radiation, and a HOE for focusing the radiation into a sample illumination beam. A sample is mounted to be examined through irradiation by the foregoing beam.
Still another aspect of the invention contemplates combining source and detector HOE's in an apparatus. A detector HOE is positioned to receive subsequent radiation from the sample which has been illuminated by the source HOE, with the detector HOE
dispersing the subsequent radiation from the sample into individually focused substantially monochromatic regions at a detector position. Again, a detector for detecting a substantially monochromatic region of the line is located at the detector position, with the detector generating a signal derived from the radiation impinging thereon.
In each of these imple~entations, the optical elements between light source and sample and those between sample and detector are designed and located to provide symmetric light paths into and out of the sample container.
The function o. both the confocal geometry in every case, and the source HOE's in particular is to minimize stray light which reaches the detectors, both within and outside of the acceptance passband for each detector, while providing maximum light throughput. Given a sample cuvette axis which is coincident with the incident line segment image and the output line segment object positions, light enters and leaves the sample cuvette normal to the cuvette surface. This geometry minimizes re'raction at these sur~aces and thereby reduces unwanted wavelength dispersion there. In addition, all rays through ~he sample have substantially identical optical path lengths because of SUBSTITUTE SHEET

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W092/~1 `' PCT/US9t/07318 this design, so th;a~ àll rays through the sample will experience substantially identical losses in intensity caused by light absorption from the sample chromophore.
Si~nal intensity at the detector is therefore largely independent of the exact path of each detected ray because of cylindrical optical symmetry around the sample cuvette.
The original QUANTUM spectrophotometer employed a confocal geometry, but focused light to and from a point focus located at the center of the sample cuvette. Light entered and exited the cuvette normal to the cuvette radius, but non-normal with respect to the cylinder axis of the cuvette, so that the detected signal was averaged over a range of optical paths through the sample.
The implementations described herein provide both confocal geometry and surface normality in both axial and radial directions to reduce aberrations and stray light.
This improves the signal-to-noise ratio of the optical system which in turn permits the uce of a lower power light source, improves the dynamic range, increases wavelength selectivity and improves the lower limit of sample d~tection. Suitably designed-and constructed HOE's give geometric and wavelength-specific transformations of light distributions which permit the matching of the optical and geometric characteristics of both the light source and the detectors to the desired sample illumination geometry. '~
A source HOE of the foregoing type is, according to one inventive techni~ue applied to bichromatic spectroscopy of an elongated light-transmissive sample, fabricated from a object beam of coherent light of a first predetermined wavelength passed through means for shaping the object beam into a generally horizon~ally focused line segment in front of a holographic recording medium surface.
A reference beam comprising a beam of coherent collimated light o~ this first predetermined wavelength is passed through reference beam focusing means which brings the reference beam to a focus behind the recording medium surface (for a transmission hologram), to yield a ,, - , - . . . ~ , . . --- . . - .

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holographic image which on playback is a first line segmentat an output focus.
A second exposure is then made using a second object beam of coherent light of a second predetermined wavelength passed through the same means for shaping the first object beam, to again yield a generally horizontally focused line segment of the second object beam in front of a holographic recording medium surface. A second reference beam comprising a beam of coherent collimated light of the second predetermined wavelength is passed through the same reference beam focusing means, again to a focus behind the recording medium surface for combination with the second object beam to yield a holographic image which on playback is a second line segment at an output focus. The first and second line segments of the foregoing holographic images are combined so that at playback they yield a substantially coaxial and congruent output line focus.
The means for shaping the object beam preferably comprises a first means for focusing the object beam, in the form of a collimator through which each object beam first passes, and then a second means for focusing each ob~ect beam to c~llectively yield a horizontally focused line segment which is at least partially vertically collimated. The reference beam focusing means preferably comprises a low F-number converging lens.
The source HOE can be a sinqle holographic plate used as the recording means, with first and second consecutive exposures of the plate corresponding to the first and second predetermined wavelengths. Alternatively, the source HOE may comprise a first holographic plate which records an image formed of the object and reference beams of the first predetermined wavelength and a second holographic plate which records an image fcrmed of the object and re~erence beams of the second predetermined wa~elength. The first and second plates are then assembled in overlappin~ arxangement to yield a substantially coaxial and congruent line focus at playback.

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W092/~ ~1 2 0 9 Q 4 &3 `; ` PCT/US91/07318 ~ ~ 12 A specific spectrophotometer made in accordance with the present invention~ using both source and detector HOE's comprises a source of multiwavelength electromagnetic radiation (e.g., white light), and a source HOE for focusing the radiation into a substantially linear sample illumination beam. The source HOE is fabricated from an object beam of coherent light~of a first predetermined wavelength passed through a coilimator and then through a lens to bring the object beam to a substantially vertically collimated horizontally focused line segment in front of a holographic recording medium. The reference beam for this portion of the source HOE comprises a collimated beam o~
coherent light of the first predetermined wavelength passed through a low F-number converging lens to a focus behind the recording medium.
A second exposure is then made with a second object beam of coherent light of a second predetermined wavelength pas$ed through the collimator and lens to bring the second object beam to another substantially vertically collimated horizontally focused line segment in front of the recording medium. A second reference beam of collimated coherent light of the second predetermined wavelength is passed through the same low F-number converging lens to a focus behind the recording medium.
The line segments of the two holographic images so formed are combined so that at playback a substantially coaxial and congruent output line segment focus is produced.
Some means is used to hold a -~ample to be examined through irradiation by the sample illumination beam from the source HOE at the output line focus of the source HOE, such that light at the output line segment focus is substantially parallel to and generally coincident with an axis of symmetry of the sample.
A detector HOE is positioned to receive subsequent radiation from the sample irradiation. The detector HOE is constructed according to one of the techniques already described, which yield a vertically SUBST~TUTE SHEEJ

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reference bea~ for the detector HOE comprises a beam of collima,ted light passed through a low F-number converging lens to a focus behind the recording medium surface.
~ he detector HOE is mounted for use such that its object line segment focus coincides with the output line focus of the source HOE, i.e., both are coaxial with the sample axis. The detector HOE disperses the subsequent radiation from the sample into a spectrum having a short vertical height at a detector position. A signal from a detector located at the detector position, is then analyzed to obtain an analysis of the sample.
Fairly low-input power requirements for the light source used in such a spectrophotometer as described above results from using both source and detector HOE's just described. The cost and assembly advantages noted by the elimination of some or ~ll of the classical optics in such a spectxophotometer are realized w~th the present invention. Also, while specific apparatuses have been described above using a detector HOE alone, or both detector and source HOE's, the present invention further contemplates the use of source HOE with or without the use of a detector HOE.
It will be understood, however, that much of the foregoing description of the invention is related to its application in spectroscopy of an elongated light-transmissive sample; hence the generation of line segments for the HOE's. The invention can broadly be considered as providing a HOE for use in generating an electromagnetic spectrum of an illuminated subject having any predetermined illuminated configuration (or image), not just a line segment. The HOE is accordingly fabricated from an object beam of coherent light which is shaped to recreate the illuminated configuration in front of a holographic recording medium surface, with the holographic medium and recreated illuminated configuration defining a selected SUBSTITIJTE S~

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orientation, such as the line segment spaced a predetermined distance from the holographic plate already described. A reference beam of the same coherent light is converged to a focus beyond the recording medium surface. -The HOE, when exposed to illumination in the form of the predetermined illuminated configuration and placed in an orientation relative to that illumination approximating the selected orientation used for recording, then produces a spectrum of the illumination at a detector position.
The objects and advantages of the present invention will be further understood upon consideration of the following detailed description of preferred embodiments of the invention taken in conjunction with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a schematic drawing of an arrangement for fabricating a detector HOE;
FIG. 2 is a schematic drawing of an arrangement for fabricating a source HOE;
FIG. 3 is a schematic drawing of a source HOE
used as a dual wavelength source element; ;
FIG. 4 is a schematic drawing of a detector HOE
used as a processing element;
FIG. ~ is a schematic drawing of a spectrophotometer using a detector HOE made in accordance with the present invention;
FIG. 6 is a schematic drawing of a spectrophotometer using both source and detector HOE's made in accordance with the present invention;
FIG. 7 is a schematic drawing of an arrangement for fabricating a reflection HOE in accordance with the present invention; and FIG. 8 is a largely schematic drawing of a prior art "QUANTUM" spectrophotometer using classical optics.

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W092/06~1 2 0 9 ~ PCT/US91/07318 15 ' . , DETAILED DESCRIPTION OF PRESENTLY PREFER~ED
E~ODIMENTS OF THE INVENTION
The present invention will now be described with relation to applications particularly adapted for use in photometric devices, and spectrophotometric apparatuses specifically. The fabrication techniques for the HOE's made in accordance with the invention are also described with particular regard to the foregoing applications. As noted in the "Background of the Invention" above, the invention had its genesis in an effort to replace the classical optics used in an absorption spectrophotometer of the type described in U.S. Patent No. 4,195,932 (and see FIG. 8 herein). Such devices are generally characterized as having a source of radiant energy, a monochrometer--that is, a device for isolating narrow bands of radiant energy from the source--a cell for holding the (liquid) source under investigation, and a device to receive and analyze the radiant energy from the illuminated sample. It will nonetheless be understood that the present invention can have application beyond the foregoing environment.
FIG. 1 shows an arrangement for fabrication of a so-called detector HOE. The technique follows the standard arrangement for fabrication of a hologram, using coherent light from a single laser to produce both object and reference beams. Here, a HeNe laser 10 is employed having wavelength of ~33 nm. A standard cube beam splitter 11 splits the laser beam into reference 12 and object reference 13 beams. The beams 12, 13 are of suitable incident directions to provide that the central axis of each beam impinges on to the holographic plate 16 at an angle of about 45 degrees to the plate normal, but with the impinging beams making a mutual angle of about 90 degrees as they recombine at the plate.
Object beam 13 is reflected off beam steering mirror 14 and first passes through a horizontally mounted, clear lens element in the form of glass rod 17 which increases the vertical divergence of the collimated laser .

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beam to generally match the output divergence of the beam from the lens-tipped lamp described below with relation to the implementation o ~':the detector HOE in a spectrophotometer (described with relation to FIG. 4 in particular)~ Alternatively, a cylinder lens may be used in place of the rod 17. It, like the rod 17, would have its major axis oriented perpendicular to the object beam 13, as well as perpendicular to the axis of the second (following) lens element (described hereafter). A glass rod of about 1/4 inch diameter was used to achieve a sufficiently short focal length to approximate that of the lamp's own lens tip.
After passing through the glass rod 17, the object beam 13 then passes through a vertically mounted lens element 18, which focuses the beam horizontally to a substantially vertical line segment -- here, at a position 25 about 6 cm. in front of the front (emulsion side) surface center of the recording plate 16. A clear, 1/2 in.
diameter test tube filled with mineral oil was initially used to achieve the effect of the test tube used in practice. Alternatively, another cylinder lens may be used in place of the oil-filled tube 18. It, like the first lens 17, would have it major axis oriented perpendicular to the object beam 13, as well as perpendicular to the axis of the clear rod 17, i.e., the axes of the two are orthogonal.
The planar face of a half cylinder lens would also be normal and downstream to the beam 13.
The reference beam 12 is reflected off a beam steering mirror 19, and then passes through a spatial filter combined with a 2 inch output diameter diffraction limited collimator 22. This yields a reduced scatter planar wavefront expanded reference beam.
The reference beam 12 then passes through a large diameter achromatic low F-number bi-convax converging lens 24. Lens 24 is located to bring the reference beam 12 to a focus at a point 20 about 6 cm. beyond the center of the rear surface of the recording plate 16. Since the hologram SU~3STITUTE SHEET

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is to be a transmission HOE which focuses an input beam to the smallest possible image spot, the reference beam focus is behind the recording plate. In application use, the focal point defines the detector position.
The recording plate 16 is mounted in a substantially vertical plane with its emulsion side facing the incident beams. The recording plate 16 is exposed for a period determined empirically to optimize the diffraction efficiency of the finished hologram. The diameter of the hologram area on the plate was adjusted to be about 3 cm.
in one suitable arrangement, so that the finished HOE had an effective F-number of about 2. The plate 16 is developed using standard processing chemistry.
FIG. ~ schematically illustrates the general arrangement and function of the detector HOE 16. The HOE
is mounted in a generally vertical plane with its emulsion side facing (upstream) the play~ack illumination source, here represented by the focus 26. As will be described with reference to a particula~ application of the HOE in a "QUANTUM"-type spectrophotometer, focus 26 will be a vertical line segment focus similar to, and at the same relative position as, the vertical llne segment focus 25 used in fabrication of the detector HOE.
In FIG. 5, light from the illumination source (26) passes through a baffle with a vertical slot aperture 27a before reaching the tube, which serves to block stray light. The detector HOE then generates a spectrum from the incident light. That spectrum has a first order image that comes to a focus in generally monochromatic segments each having a small vertical height. One or more detectors in the form of silicon photodiodes 28a, 28b are located at the respective foci of the substantially monochromatic peak and sideband wavelengths that are to be analyzed. The photodiodes are mounted with their faces nor~al to the in~ident light. The photodiodes 28a, 28b generate an electrical signal, which is then amplified by suitable amplifiers 29 which in turn are part of the signal SUBSTITllT~ SHEET

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- . , . ~ .. .. . , . ... . . . . -WO92/06361 2 0 9 0 4 8 3`~ '` Pcr/usgl/073l processing means, such as including digital voltmeters 52, used to analyze the signals, as for absorption analysis of a sample. ; ~
l0 nm bandpass filters (not shown) centered at the peak and sideband wavelengths are placed alternately in front of the lamp used as the light source (see, e.g., FIG. S) and in front of the corresponding detector to position the detectors so as to maximize the output from a respective amplifier board. An additional aperture or baffle 27b can also be positioned after the HOE 16, as well as apertures 53 in front of the photodiodes 28a, 28b, again to limit stray light onto the photodiodes.
It will be understood that the distances chosen for foci, as well as the particular collimator, beam-splitters, cylinder lenses and the like can be varied with the intended application of the finished HOE. As already noted, the arrangements described herein were designed with a particular application in a spectrophotometer of the type sold by Abbott Laboratories under the trademark "QUANTUM".
Fabrication of the HOE's in this detailed description thus tended to roughly duplicate the same optical organization of the "QUANTUM."
FIG. 2 illustrates a fabrication arrangement for a so-called source HOE. It will nonetheless be recognized that, although denominated as a source HOE, the same could function as the foregoing detector HOE, as will be made more evident with respect to the descriptions of the applications of both HOE's to follow.
Fabrication of this particular source HOE
employed a ~eNe laser l0 having a wavelength of about 633 nm and an argon ion laser 30 having a wavelength of about 488 nm. Again, since the "QUANTUM" spectrophotometer analyzes a particular peak and sideband wavelength, the foregoing laser wavelengths were chosen to be as close as possible to the preselected peak and sideband absorption wavelengths for spectroscopic analysis to reduce SUB~TiTUTE SHEET

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~ WO92/06361 2 0 9 0 ~ 8 ~3 ~ ` Pcr/us91/o73l8 , 19 aberrations in use. Other wavelengths could be readily chosen, depending on the desired application.
The lasers 10, 30 are used for consecutive exposures of one or more holographic plates. To facilitate use of the same general arrangement for such consecutive exposures, a movable beam-steering mirror 31 was used to direct respective laser beams to the beam-splitter 11.
Movable beam dumps (not shown) could also be employed.
As in the fabrication of the so-called detector HOE, the beam from a selected laser is split into an object beam 13' and a reference beam 12'. Object beam 13' is, in this fabrication technique, reflected off beam steering mirror 14 and first passed through a diffraction-limited 1 inch output diameter collimator 35, and then through a vertically oriented cylinder lens 36. What results is a beam which is vertically collimated and horizontally imaged to a line segment brought to a focus 37 about 6 cm. before the front surface center of the recording plate 40. This same technique, using a collimator and cylinder lens combination, could also be applied for forming the object the fabrication of the detector HOE previously described.
Reference beam 12~ is reflected off beam steering mirror 19 and through a spatial filter combined with a 2 inch output diameter diffraction limited collimator 22 to give a reduced scatter, planar wavefront for the expanded beam. Beam-steering mirror 23 then directs the beam 12' through an achromatic converging lens 24 to a focus 20 at a point about 6 cm. beyond the rear surface of the recording plate 40. The converging lens 24 has a 50 mm diameter, and a focal length of 100 mm for a low F-number of about 2. All of the cylinder lenses described herein, being used for beam convergence, have their respective planar faces located downstream relative to the impinging beam, and substantially normal to the beam. The major (or only) axis of each cylinder lens establishes the orientation of the cylinder lens "vertical" or "horizontal"
relative to the roughly horizontal plane of the overall ~ i ~ U S ~ L~

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set-up. In general, the more curved lens surface faces the more fully collimated beam~.~so in fabrication, the curved face of the cylinder ~e~s faces the collimator.
~., The respective central axes of beams 12', 13' impinge on the holographic plate 40 at an angle of about 45 degrees to the plate normal. The beams 12', 13 make a mutual angle of about 90 degrees at recombination at the plate 40. Other angles for the beams can be chosen, of course, so long as they yield a fringe spacing which is suitable for recording and provide adequate wavelength dispersion at playback of discrete monochromatic segments (for a spectrophotometric application).
A first exposure of plate 40 is made in the foregoing manner using laser l0 again with the exposure for a period determined empirically to optimize the diffraction efficiency of the finished hologram. The diameter of the hologram area on the plate was selected to be about 3 cm.
in one suit~ble arxangement. The finished HOE had an effective F-number of about 2. A second exposure is then made using the same arrangement as that described for the first exposure, but this time using the laser 30, small adjustments being made in the arrangement to accommodate the different wavelength, such as refocusing of the collimator/spatial filter combinations. This second exposure can be on a different plate, or could be on the same plate 40.
A source HOE made using two plates had both plates 40', 40" (see FIG.3) consecutively mounted in a nearly vertical plane for exposure. The first plate had its emulsion side facing toward (upstream) the incident beams for the source sideband HOE. For the source peak HOE, the emulsion side faced away (downstream) from the beams, with a spacer glassplate separating the hologram plate and its holder.
That is when two plates were used, the second was turned with its emulsion side away from the beams and a stripped glass spaced inserted to place the emulsion at the .

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~ W092/~1 2 ~ 9 0 ~ 8 3 t; '' ~ ` PCT/US9l/07318 same position as for the first plate. In this manner, both HOE gratings faced the same "lamp distance~ at playback, and formed a common line output image. Accordingly, the fabrication optics are to be independently optLmized for each wavelength. Given the physical constraints of the holographic plates, how the plates are arranged on combination to make the images coincide also becomes a fabrication consideration.
With this choice of plate orientations for exposure, the source sideband HOE 40' is mounted in use in a spectrophotometer with its emulsion side 40a' toward the illumination focus 50. The source peak HOE 40" is mounted to play back with its emulsion side 40a-' away from the illumination focus 50. The HOE ' s 40 ', 40" are clamped together loosely in facial engagement in this orientation such that the two HOE's have a substantially common or congruent line image for their intended central peak wavelengths at playback.
For playback, a small lens-tipped incandescent lamp 51 is mounted approximately at the intenaed common reference beam point focus of the two ~oined plates 40', 40". The source HOE 40 (plates 40', 40") is mounted in a vertical orientation such that the central axis of the cone of light from source 51 impinges at an angle of about 45 degrees to the combined plate normal, with the two emerging images produced by the respective plates focusing as substantially congruent vertical line segment images. That is, the plates 40', 40" are arranged such that a holographic image is produced on playback which is a combination of the first and second playback line segments produced by the respective plates, brought together in a substantially coaxial and congruent illumination line image 50. This arrangement of the plates will require some horizontal displacement of the plates relative to each other until the positions of their respective line segment outputs coincide as closely as possible. Lamp/plate distance and beam/plate angle are obviously empirically .
, .
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adjusted to optimize the coincidence of the two output line segments. Suitable apertures or baffles for the lamp 51 (as represented by baffle 53) and at the image 50 (FI~.6) limit stray light. Also, appropriate l0 nm interference filters ~not shown) placed betw~en the lamp 51 and the source HOE 40 are advantagéously employed for system alignment.
The order of the HOE's 40', 40" can be reversed if their orientations during fabrication are reversed.
Also, the necessity of facing the emulsion side toward or away from the intended illumination focus 50 is considered to be largely a function of the type of plate used, i.e., the thickness of the emulsion, the thickness of the plate, etc. For a multiplexed source HOE, for example, the single plate would be exposed with its emulsion side facing (toward) the beams for both exposures.
As noted above, the application for which the present invention had as its genesis was as a "QUANTUM"-type absorption spectrophotometer. FIG. 8 illustrates the general make-up of the "QUANTUM" in point. The major elements of the "QUANTUM" included a lamp 60, a first converging (e.g., plano convex) lens 62, and a second converging lens 63. A cuvette 66 was mounted in a guide or holder 67 between these lenses 62, 63 at the approximate focus of the first lens 62. An infrared filter (not shown) was located before the cuvette and adjacent to the lens 62 to protect the contents of the tube from heat generated by the light source (such as a 12 watt tungsten halogen lamp).
Peak and sideband interference filters 68 and 69, respectively, were used in combination with a dichroic beam splitter 70 to isolate the wavelengths selected for detection by the detectors 7l (only one being shown)~ The electronics to analyze the signals generated by the detectors 71 for absorption analysis in^luded a suitable analog ts digital converter. Housing 74 contained all of the foregoing "QVANTUM" elements. ~ore speci~ic detail on the type and arrangement of the elements used in the , SU~3STITUTE SHEE~

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With reference to FIG. 5, an early version of the present invention applied in use as a detector HOE for a "QVANTUM"-type spectrophotometer is depicted. A light source 80 in the form of a Gilway 1021 lens-end technical lamp rated at 3.5 v at .6A (2.1 watts) was used, and driven by a power supply 81. A cylinder lens 82 having a focal length of 25.4 mm was located in a vertical orientation with its planar face normal to the incident light beam at about 64 mm from the tip of the lamp 80. An aperture 83 consisting of ~ vertical slot was located before the sample holder/cuvette. The light into the cuvette was perpendicular to the curved surface of a cuvette mounted in the holder (i.e., along the minor axis of the cylindrical cuvette) and substantially coincident with the cuvette ma~or axis.
A detector HOE 16 fabricated as described above was mounted in the manner shown in FIG. 4. Detectors 28a, 28b were po8 itioned at respective monochromatic segment foci as previously noted.
FI~. 6 illustrates a "QUANTUM~-type spectrophotometer arrangement using both source and detector HOE ' 9 made as previously described. A miniature lens tipped bulb 51, such as a ~ilway 1021, is used to illuminate a source HOE 40 mounted as discussed above (e.g., see FIG. 3 and its associated description). Lamp Sl is located off-axis relative to the plate normal of the source HOE 40, to reproduce the conjugate to the original reference beam and thus to play bac~ the real imAge of the vertical line segment object. A cuvette holder 86' is located such that the major axis of a cuvette therein is roughly coinciden~ (coaxial) with the combined line segment focus 50 of the source HOE 40 to minimize distortion. A
slotted tube holder 86' is advantageously used to reduce stray light.

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A detector HOE 16 is mounted in the manner previously described (see, e.g., FIG. 4 and its associated d0scription), such that the source mage line focus 50 and the playback illumination o~ë~t for the detector HOE
(represented by the focus 26 in FIG. 4) coincide. Again, the axis of the focus 50 is located off-axis relative to the plate normal of the detector HOE 16, so that the original object beam is accurately reproduced and imaged into a spot at the location of the original reference beam's point of convergence, corrected for wavelength. The arrangement of the detectors 28a, 28b and other elements associated with the detector HOE 16 are as described in relation to FIG. 4.
The detectors, HOE's, lamp, apertures and baffles are adjusted interactively to obtain the maximum output signal or each wavelength being detected. All of the elements of the spectrophotometer of FIG. 6 using source 7 a~d detector HOE's are housed within a casing or housing 90 .
It is considered to be within the scope of the present invention to provide for a multiple passband bichromatic spectrophotometer. For instance, the apparatus of FIG. 6 can be constructed such that the source HOE 40 is -readily replaceable with another having different passband wavelengths. lnterchangeable source HOE's could thereby be employed for selected wavelength pairs. A photodiode array would then replace the two detectors described.
Interchangeable detector HOE's could also be similarly employed.
Use of the present invention for reflectance spectroscopy is also envisioned. Thus, rather than collecting light transmitted through a liquid sample, light reflected -- whether diffusely or specularly -- from a solid sample could be collected and processed by the detector HOE. The low F-num~er of the HOE ensures that a large fraction of such diffuse or reflected light is collected.

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~ W092/0636~ 2090~`~`3 ~ - Pcr/us9l/073l8 Source and detector HOE's could also be combined for use in a fluorescence mode of operation. For example, the source HOE would have its desired passband centered at a shorter wavelength than that of the detector HOE.
Surface or liquid fluorescence analysis could be made.
Also, while the invention has been specifically described with relation to transmission holograms, reflection holograms could be made and used. As shown in FIG. 7, fabrication of a reflecting detector HOE would utilize an arrangement similar to that of FIG. 1, except that the focus 20 of the reference beam 12 is on the "same side" of the plate 16, i.e., foci 20 and 25 are "in front of" the plate. A cylinder lens 36 is shown in place of the transparent rod 18.
Thus, while the invention has been described with relation to certain presently preferred embodiments, those with skill in this art will recognize other modifications of the invention which will still fall within the scope of the invention, as expressed in the accompanying claims.

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Claims

What is claimed is:

1. A photometer comprising:
a source of multiwavelength electromagnetic radiation, means for shaping said radiation into a sample illumination beam, means for holding a sample to be examined through irradiation by said beam, a multifunctional holographic optical element (HOE) positioned to receive subsequent radiation from said sample irradiation, said HOE dispersing said subsequent radiation from said sample into a set of individually imaged substantially monochromatic regions, means for detecting at least one region of said set of regions, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

2. A photometer comprising:
a source of light, means for shaping light from said source to a line at a line image, means for holding a sample to be examined at said line image such that light from said line image illuminates said sample, with said line image being substantially parallel to and generally coincident with an axis of symmetry of said sample, a detector holographic optical element (HOE) positioned to receive light from said sample illumination, said HOE dispersing said light from said sample into a continuous spectrum having a short vertical height at a detector position, means for detecting at least one substantially monochromatic portion of said spectrum located at said detector, said detecting means generating a signal derived from the light impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

3. A spectrophotometer comprising:
a source of multiwavelength electromagnetic radiation, means for converging said radiation to a line segment for use as a sample illumination beam, means for holding a sample to be examined through irradiation by said beam, with said line segment being substantially parallel to and generally coincident with an axis of symmetry of said sample, a detector holographic optical element (HOE) positioned to receive subsequent radiation from said sample irradiation, said HOE being constructed from an object beam of coherent light passed through means for shaping said object beam into a vertically collimated horizontally converged image line segment in front of a holographic recording medium surface, with a reference beam comprising a beam of the same coherent light which is collimated and then passed through a low F-number converging lens to an image focus behind said recording medium surface, said HOE
dispersing said subsequent radiation from said sample into a spectrum having a short vertical height at a detector position, means for detecting a substantially monochromatic portion of said spectrum located at said detector position, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

4. A spectrophotometer comprising:
a source of multiwavelength electromagnetic radiation, means for focusing said radiation into a substantially linear segment for a sample illumination beam, means for holding a sample to be examined through irradiation by said beam, with said beam being generally coaxial with an axis of symmetry of said sample, a detector holographic optical element (HOE) positioned to receive subsequent radiation from said sample irradiation, said HOE being constructed from an object beam comprising a beam of coherent light passed through a first means for focusing said light beam to provide at least partial collimation along a first axis and through a second means for focusing said light beam to provide substantial beam convergence along a second axis which is perpendicular to said first axis, said first and second means for focusing collectively yielding a line segment along said second axis in front of a holographic recording medium surface, with a reference beam of the same coherent light converging to an image beyond said recording medium surface, said HOE dispersing said subsequent radiation from said sample into a spectrum having a short vertical height at a detector position, means for detecting a substantially monochromatic portion of said spectrum located at said detector position, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

5. A spectrophotometer comprising:
a source of white light, a first cylinder lens mounted to focus at least a portion of said white light to a line image, means for holding a light-transmissive sample to be examined which sample is contained in a transparent tubular container, said sample holding means positioning said sample at said white light line image such that light from said white light line image illuminates and passes through said sample, with said white light line image being substantially parallel to and generally coincident with an axis of symmetry of said sample, a detector holographic optical element (HOE) positioned to receive light transmitted through said sample, said HOE being a transmission HOE fabricated from an object beam comprising a beam of coherent light passed through a second cylinder lens having an axis and a planar face with said planar face mounted normal to said light beam for at least partial vertical beam collimation and then through a third cylinder lens having an axis and a planar face with said third lens planar face mounted normal to said light beam and with said third lens axis perpendicular to said second cylinder lens axis to provide horizontal beam convergence, said second and third cylinder lenses collectively yielding a vertically expanding horizontally converged line segment as the object source at a predetermined distance in front of a holographic recording medium surface, with a reference beam comprising a beam of said coherent light which is collimated and then passed through a low F-number converging lens to an image point located at a distance behind said recording medium surface, said object and said reference beams each having a respective central axis impinging on said recording medium surface at an angle to said recording medium surface normal with said beam axes making a mutual angle at recombination which yields a fringe spacing suitable for recording and adequate to provide sufficient wavelength dispersion at playback such that said detector HOE, when mounted with its recorded object line segment generally coincident with that of a playback beam in the form of said white light line image, disperses light from said sample into a linear spectrum having a small vertical height at a detector position, means for detecting at least one substantially monochromatic portion of said spectrum located at said detector position, said detecting means generating a signal derived from the light impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

6. A low-input power bichromatic spectrophotometer comprising:

a source of light comprised of at least two wavelengths in the visible spectrum, said light source having a low-input power of about 1.5 watts, a first cylinder lens mounted to focus at least a portion of said white light to a line at a source line image, a cuvette holder for holding a liquid light-transmissive sample to be examined contained in a transparent cuvette, said holder positioning said sample at said source line image with said source line image substantially coincident with a cuvette major axis such that light from said line focus illuminates and passes through said sample, a detector holographic optical element (HOE) positioned to receive light transmitted through said sample, said HOE being a transmission HOE fabricated from a laser beam which is split into object and reference beams of coherent light, with said object beam passed through a second cylinder lens having an axis and a planar face with said second lens planar face mounted normal to said object beam for at least partial vertical beam collimation, and then through a third cylinder lens having an axis and a planar face with said third lens planar face mounted normal to said object beam and with its axis perpendicular to said second cylinder lens axis to provide horizontal beam convergence, said second and third cylinder lenses col-lectively yielding a horizontally converged line segment of a predetermined distance in front of a holographic recording medium surface as an object image, with said reference beam passed through a spatial filter combined with a diffraction-limited collimator to produce an expanded reduced scatter planar wavefront which is then passed through a low F-number converging lens of about F/2 to a near point image located at a distance behind said recording medium surface, said object and said reference beams each having a respective central axis impinging on said recording medium surface at an angle to a recording medium surface normal with said central axes making a mutual angle at recombination that yields a fringe spacing which is suitable for recording and adequate to provide a wavelength dispersion at playback of discrete monochro-matic regions, said HOE dispersing said light from said sample into a spectrum at a detector position, at least two photodetectors for respectively detecting a peak and sideband portion of said spectrum located at said detector position, said photodetectors generating a signal derived from the light impinging thereon, means for analyzing said signal to obtain an analysis of said sample, and a casing housing said light source, said first cylinder lens, said cuvette holder, said HOE and said photodiodes, said casing further including a first light-blocking baffle between said light source and said first cylinder lens to block stray light from said light source, a second light-blocking baffle between said cuvette older and said HOE to block stray light from said illuminated sample, and mask means for masking said photodiodes from substantially any light other than said respective peak and sideband light portions.

7. A photometer comprising:
a source of multiwavelength electromagnetic radiation, a source holographic optical element (HOE) for shaping said radiation into a sample illumination beam, means for holding a sample to be examined through irradiation by said beam, a detector HOE positioned to receive subsequent radiation from said sample irradiation, said detector HOE
dispersing said subsequent radiation from said sample into individually focused substantially monochromatic regions at a detector position, means for detecting at least one substantially monochromatic region located at one of said detector positions, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said; signal to obtain an analysis of a sample.

8. A spectrophotometer comprising:
a source of multiwavelength electromagnetic radiation, a holographic optical element (HOE) for focusing said radiation into a source line segment image for a sample illumination beam, said source HOE being fabricated from an object beam of coherent light of a first predetermined wavelength passed through a collimator and then through a cylinder lens having a major axis and a planar face with said planar face mounted normal to said object light beam to bring said object beam to a substantially vertically collimated horizontally converged object image line segment in front of a means for recording a holographic image, with a reference beam comprising a collimated beam of coherent light of said first predetermined wavelength passed through a low F-number converging lens to a near point image behind said recording means, and a second object beam of coherent light of a second predetermined wavelength passed through said collimator and cylinder lens to bring said second object beam to another substantially vertically collimated horizontally converged image line segment in front of said recording means, with a second reference beam of collimated coherent light of said second predetermined wavelength passed through said low F-number converging lens to a near point image behind said recording means, said image line segments of said holographic images being combined to produce at playback a substantially coaxial and congruent output line segment at an output image, means for holding a sample to be examined through irradiation by said sample illumination beam at said output line image such that said output image is substantially parallel to and generally coincident with an axis of symmetry of said sample, a detector HOE fabricated from an object beam comprising a beam of coherent light passed through means for focusing said object beam to a vertically collimated horizontally focused line segment object in front of a holographic recording medium surface, with a reference beam comprising a beam of said coherent light passed through a collimator and then through a low F-number converging lens to a near point image behind said recording medium surface, said detector HOE mounted for use such that its line segment object coincides with said output image of said source HOE, said detector HOE dispersing said subsequent radiation from said sample into a spectrum having a short vertical height at at least two detector positions, means for detecting a substantially monochromatic portion of said spectrum located at each of said detector positions, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said signals to obtain an analysis of said sample.

9. The spectrophotometer of Claim 8 wherein said source HOE is formed of a single holographic plate used as said recording means, first and second exposures of said plate being used for said first and second predetermined wavelengths, respectively.

10. The spectrophotometer of claim 8 wherein said recording means comprises a first holographic plate which records an image formed of said object and reference beams of said first predetermined wavelength and a second holographic plate which records an image formed of said object and reference beams of said second predetermined wavelength, said first and second plates being assembled in overlapping arrangement to yield a substantially coaxial and congruent output line image at playback.

11. A spectrophotometer comprising:
a source of white light, a source holographic optical element (HOE) for focusing said radiation into a substantially linear line segment for a sample illumination beam, said source HOE
being made an object beam of coherent light of a first predetermined wavelength passed through a collimator and then through a cylinder lens having a major axis and a planar face with said planar face mounted normal to said object beam to bring said object beam to a substantially vertically collimated horizontally converged line segment in front of a means for recording a holographic image, with a reference beam comprising a collimated beam of coherent light of said first predetermined wavelength passed through a low F-number converging lens to a near point image behind said recording means, and a second object beam of coherent light of a second predetermined wavelength passed through said collimator and cylinder lens to bring said second object beam to another substantially vertically collimated horizontally converged line segment in front of said recording means, with a second reference beam of collimated coherent light of said second predetermined wavelength passed through said low F-number converging lens to a near point image behind said recording means, said line segments of said holographic images being combined to produce at playback a substantially coaxial and congruent output line segment at an output line segment image, means for holding a light-transmissive sample to be examined through irradiation by said sample illumination beam at said output line segment image such that said output line segment image is substantially coaxial with an axis of symmetry of said sample, a detector HOE positioned to receive light transmitted through said sample, said detector HOE being a transmission HOE fabricated from an object beam comprising a beam of coherent light passed through means for focusing said light beam to a generally horizontally converged line segment object at a predetermined distance in front of a holographic recording medium surface, with a reference beam comprising a beam of said coherent light passed through a collimator and then a low F-number converging lens to a near point image located behind said recording medium surface, said object and said reference beams of said detector HOE each having a respective central axis impinging on said recording medium surface at an angle to a recording medium surface normal with said axes making a mutual angle at recombination which yields a fringe spacing suitable for recording and adequate to provide sufficient wavelength dispersion at playback such that said detector HOE when mounted with its input line segment object coinciding with the output line segment image of said source HOE disperses light from said sample into a spectrum having a small vertical height at a detector position, means for detecting a substantially monochromatic portion of said spectrum located at said detector position, said detecting means generating a signal derived from the radiation impinging thereon, and means for analyzing said signal to obtain an analysis of said sample.

12. A low-input power spectrophotometer comprising:
a source of light comprised of at least two wavelengths in the visible spectrum, said light source having a low input of about 1.5 watts, a source holographic optical element (HOE), said source HOE being fabricated from an object beam of coherent light of a first predetermined wavelength corresponding to one of said two wavelengths which is passed through a collimator and then a cylinder lens having a major axis and a planar face with said planar face mounted normal to said object beam to bring said object beam to a vertically collimated horizontally converged line segment in front of a means for recording a holographic image, with a reference beam comprising a spatially filtered collimated beam of coherent light of said first predetermined wavelength passed through a low F-number converging lens to a near point image behind said recording means, and a second object beam of coherent light of a second predetermined wavelength corresponding to the other of said wavelengths passed through said collimator and said cylinder lens to again bring said second object beam to a vertically collimated horizontally converged line segment in front of said recording means, with a second reference beam of spatially filtered collimated coherent light of said second predetermined wavelength passed through said low F-number converging lens to a near point image behind said recording means, said line segments of said holographic images so formed being combined at playback to a substantially coaxial and congruent output line segment image, a cuvette holder for holding a liquid light-transmissive sample to be examined contained in a transparent cuvette, said holder positioning said sample at said output line segment image with said output line image substantially coaxial with a cuvette major axis such that light at said line focus illuminates and passes through said sample, a detector holographic optical element (HOE) positioned to receive light transmitted through said sample, said detector HOE being a transmission HOE
fabricated from a laser beam which is split into object and reference beams of coherent light, with said object beam passed through means for producing a vertically collimated horizontally converged line segment as an input image at a predetermined distance in front of a holographic recording medium surface, with said reference beam passed through a spatial filter combined with a diffraction-limited collimator to produce an expanded reduced scatter planar wavefront which is then passed through a low F-number converging lens of about F/2 to a near point image located at a distance behind said recording medium surface, said object and said reference beams for said detector HOE each having a respective central axis impinging on said recording medium surface at an angle to a recording medium surface normal with said axes making a mutual angle at recombination that yields a fringe spacing which is suitable for recording and adequate to provide a wavelength dispersion at playback of generally discrete monochromatic regions, when said detector HOE is mounted with its input image line segment generally coaxial with said source HOE
output line segment image, said HOE dispersing said light from said sample into a spectrum at a detector position, at least two photodetectors for respectively detecting a peak and sideband portion of said spectrum located at said detector position, said photodetectors generating a signal derived from the light impinging thereon, means for analyzing said signal to obtain an analysis of said sample, and a casing housing said light source, said source HOE, said cuvette holder, said detector HOE and said photodetectors, said casing further including a first light-blocking baffle between said light source and said source HOE to block stray light from said light source, a second light-blocking baffle between said cuvette holder and said detector HOE to block stray light from said illuminated sample, a third baffle between said detector HOE and said photodetectors to block stray light, and mask means for masking said photodetectors from substantially any light other than said respective peak and sideband light portions.

13. A method for fabricating a holographic optical element (HOE) for use in generating an image of a substantially monochromatic spectral region to illuminate a subject having a predetermined illumination configuration comprising the steps of:
providing an object beam of coherent light, focusing said object beam to create an image in the form of an idealization of said illuminated configuration whereby one or both dimensions of said image approach the diffraction limit, and with an image shape, dimensions and distance from the holographic plate as nearly identical as possible to those of an object of an HOE designed and fabricated to collect, focus and disperse light from the same subject, place a holographic recording medium surface in a selected orientation relative to said image and at a predetermined distance from said image, providing a reference beam of the same coherent light, converging said reference beam to small focus beyond said recording medium surface, exposing said holographic recording medium to said object beam and reference beam to produce a recorded hologram, developing said exposed holographic recording medium into a fixed hologram, said HOE, when illuminated by multi-wavelength light from a light source whose shape is idealized by the shape of said reference beam focus, and placed in an orientation relative to the subject approximating the selected orientation used for recording and at said predetermined distance, producing an image of the appropriate dimensions, position and orientation at a position to serve as the input for said HOE designed and fabricated to collect, disperse and focus light from the same subject.

14. A holographic optical element (HOE) made by the method of claim 13, and further comprised of two such HOE's each fabricated to generate an image of a single substantially monochromatic wavelength region at a single, predetermined image position, with said two HOE's placed together to produce coinciding, substantially monochromatic images which can be produced at said image position.

15. A holographic optical element (HOE) made by the method of claim 13, and further comprised of a single hologram formed by exposures to two different monochromatic wavelengths, with said exposures being made to produce coinciding substantially monochromatic images which can be projected at said image position.