DE1956443A1 - Multicolor holography - Google Patents

Description

1356443

PATENT LAWYERS

PR. O. DlTTMANN K, L. SCHIFF DR.A.v.FUNER DlPL ·. ING. P, StRBHL

PATBNTANWaLTK 8 MÜNCHEN SB POSTFACH 8B 01BQ Q MUNICH 90

MARtAHiLP] PIjATZ 2 & 3

fiolotron Corporation phone: <ο8ϊϊ) 4S4O4o & 443244

TT i ι j. ϊλπ 'xrz-i τ / TT no. \ TBLEOR.} EUROMARCPAT MUNICH

Our ict DA-K511 (H-39)

November 10, 1969 ELS / Hö.

Multicolor holography

(Priority: USA Application No. 774 712 dated November 12, 1968)

Abstract:

Improved technology and facilities for construction of a Ηοίος / Γαίητηβ, which is used to reconstruct a multicolored image by means of white light is suitable. i £ in picture of the to be recorded The object scene is focused on or near a hologram detection plane from one side thereof, while a reference radiation coherent with the radiation illuminating the scene of the object is directed to the opposite side of the hologram detection plane.

Background of the invention:

The invention relates generally to holography and in particular to improvements in color holographic

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phy, whereby incoherent white light can be used to reconstruct a full color image of improved quality »

A general discussion of the fundamental holographic techniques is found in an article "Advances in Holography ¹ " by KS Pennington, in the February 1968 journal, pages 40-48. Basic off-axis holographic techniques, both monochromatic and also multicolored, are disclosed and claimed in the pending application 'P 14 72 071.9 (our file DA-K216 (HI)) and in separations thereof. In short, out-of-axis holography involves directing two bundles of coherent radiation at a finite angle between them onto a radiation detection surface to interfere with one another. A radiation beam is modified by an object scene before it hits the detection surface. The most popular form of outer-axis holography uses visible light as radiation and photographic film as the detection surface. The photographic film thus records both phase and amplitude information relating to the subject _scene, which can later be used to reconstruct a fully three-dimensional image of the recorded subject scene. Once developed, the film is illuminated with a point source of light which must be essentially monochromatic in order to avoid chromatic scattering which would cause a reconstructed image of poor resolution. Such chromatic scattering has the effect, for example, that a small point on the object appears as a larger, blurred point in the image. This prevents the use of ordinary white light sources for reconstructing images of such holograms.

In a basic color holography technique, two or more pairs of coherent beams of radiation are used

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Interference placed on a photographic plate, each pair having a particular wavelength within one of the primary ones Has colors. One bundle of each pair is modified by the subject scene and the unmodified reference bundle meets the photographic film directly. Each pair of coherent bundles creates a particular diffraction pattern, that records the source front of the subject scene as if it were through the single wavelength of light of the particular coherent bundle pair would be illuminated. When reconstructing a color image, each of the diffraction patterns is marked with a separate monochromatic beams of the same wavelength that used for its construction. This generally uses the same coherent source as that used for the Reference bundle was used during construction. Furthermore, in the construction of such a hologram, the various Reference bundle · from each other through different angular positions separated to avoid ghosting which would interfere with the desired multicolored image when viewed. Around the plurality of monochromatic images to produce a To superimpose a full multicolored image of the subject scene, the reconstructing light sources must be in the same Be aligned in the manner in which the reference beams were aligned with respect to the hologram. This basic color holographic process is disclosed in the aforementioned application P 14 72 071.9 or a separation thereof.

Many alternative techniques for color holography have been suggested, which in certain circumstances are preferred where it is inconvenient to reconstruct a multicolored image with multiple monochromatic light sources and these Sources precisely related to the hologram and to each other, such as the reference bundle sources used in the construction of the hologram having to align. One such technique is called

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Backlight holographic method; at this one the coherent radiation modified by the object and the reference radiation hit the photographic one from different angles Film on to eliminate interference fringes within the volume of the photographic emulsion. This technique has advantages under certain circumstances, since the reference radiation can be a single beam that is coherent for single wavelengths Contains light bundles that are coaxially aligned by means of ordinary optical elements and directed onto the film will. Furthermore, the reconstructing radiation can be an ordinary white light source, as a volume hologram constructed in this way has a filter effect in such a way that every special diffraction pattern generated in the film emulsion, only a narrow range of wavelengths around the single coherent wavelength used in the construction of the particular diffraction pattern Accepting bundles around; this makes chromatic scattering acceptable for certain holographic applications Limits restricted. Back-lighting holography techniques are discussed more fully in the literature such as in an article by Upatnieks and others in "Applied Physics Letters" Vol.8, No. 11, page 286 (1966). Kück lighting techniques are also in the pending patent application P 15 47 202.3 - our files DA-K227 (H-5) - disclosed and claimed.

Another method of reducing chromatic scattering when reconstructing images from a hologram consists in the holographic technique of the focused image. It was recognized that when the subject scene in the construction of the hologram is placed very close to the photographic film, the reconstructed image is itself close to the Holograms are located and thereby the blurring effect of the chromatic scattering when using a polychromatic 'Prevents reconstructing light source. As it is often physically

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it is difficult to bring a subject scene very close to the photographic film during the construction of a hologram, the subject scene is generally created through the use of a suitable optical system in or near the Hologram plane mapped. The focused image holographic process is described by Kock et al in "Proceedings of the IEEE "from January 1967 for monochromatic image reconstruction described.

The invention aims to improve the techniques of outer-axis focused imaging as well as holography the outer-axis back bundle color holography Techniques for generating a hologram, the reconstruction of a multicolored one Image of improved resolution with a polychromatic light source allowed.

Summary of the Invention;

The foregoing and other objects of the invention will be achieved achieved by combining the aforementioned monochrome focused imaging technique and the back bundle multicolor image technique, to produce a hologram, the reconstruction of a multicolor image of the recorded subject scene with ordinary white light and that a higher degree of Sharpness than can be achieved with either the back bundle or the focused imaging technique alone. A Image of a subject scene focused on or near one side of a hologram detector is made holographic by Illumination of the opposite side of the detector recorded with reference radiation. Both radiations, the reference radiation and the radiation illuminating the subject scene contain a plurality of distinct coherent bundles or rays different wavelengths.

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A better understanding of the invention and its applications to preferred embodiments emerges from the following description and the accompanying drawings.

Brief description of the drawings;

In the drawings illustrate:

Figure 1 illustrates a known technique of constructing a monochrome focused image hologram;

. Fig. 2 Reconstruction with polychromatic light of a "holograms produced according to the technique of FIG. 1;

Figure 3 illustrates a prior art technique of constructing a multicolor backbeam hologram;

F-j. 4 shows a technique for reconstructing a multicolored one

ldes with white light from one according to the technique of Fig. generated hologram;

Figure 5 shows an embodiment of the invention incorporating the techniques of the focused image and the return bundle are combined to produce a hologram, of which a multicolored image is provided can be reconstructed with improved resolution-;

6 shows a technique of reconstruction with white light of the improved hologram produced according to the technique of FIG. 5;

7 and 8 schematically the improved diffraction properties of a hologram constructed according to the invention; and

9 and 10 show another embodiment of the invention in which a master hologram recorded according to the techniques of the invention is used to generate a three-dimensional real color image. _{Q Q}

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Description of the preferred embodiments "

A technique of constructing a focused image hologram using electromagnetic, within the visible Radiation lying in the range of wavelengths is illustrated in FIG. 1. A sheet of 'photographic film 11 is made illuminated with an image 13 of an object scene 15. The subject scene 15 is provided with a coherent subject light beam 17 illuminated, this being bundle of the subject scene 15 is modified and reflected to produce an object-modified Bundle 19. The bundle 19 modified by the object is carried out for the purpose of generating the object image 13 a lens 21 controlled = a reference light beam 23, which is coherent with the object beam 17, illuminates the photographic Film 11 likewise, and caused interference between the reference beam 23 and the beam 19 modified by the object recorded on the photographic film 11, thereby both phase as well as amplitude information of the subject scene 15.

Developing the photographic film 11 in the usual way results in a hologram 11 * from which a fully three-dimensional image of the subject scene 15 can be reconstructed. A polychromatic reconstructing point source 25 supplies a reconstructing beam 27 similar to the reference beam 23. The reconstructing beam 27 illuminates the hologram 11 * to produce an image 29. The sharpness at any given point of the image 29 depends on the wavelength range of the reconstructing beam 27 and on the distance of such point from the emulsion surface of the photographic film 11 *. Points of the image 29 which lie in the plane of the emulsion of the photographic film 11 * are sharp, even if the reconstructing light bundle 27 comprises an extremely wide range of wavelengths.

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However, to the extent that a given point of interest of the image 29 further differs from the emulsion of the photographic Film 11 'moves away, the wavelength range must of the reconstructing bundle 27 can be greatly restricted if the reconstructed point is to be sharp.

The construction of a color image hologram backlit with white light shall be described with reference to FIG Fig. 3 will be briefly described. A sheet of photographic film 31 is illuminated from one side thereof by a reference light beam 33 that contains at least two wavelengths of coherent illumination, such as a wavelength in red and a wavelength in the green. An object scene 35 is illuminated with an object bundle 37 having the same plurality of coherent radiation wavelengths as the reference beam 23 and that in general through the same as the that Reference beam 33 generating laser light source or sources is generated. The object scene 35 reflects and diffuses the bundle of objects 37 to produce an object-modified bundle 39 which is imposed on the photographic film 31 a side meets the opposite law to that of the reference bundle 33 acted upon side lies. A separate diffraction pattern is within the volume of the photographic emulsion of the photographic film 31 by interference between each of the Generated multiple wavelengths used. Each separate diffraction pattern diffracts only a narrow area when reconstructed of wavelengths around the single wavelength used to generate the diffraction pattern, assuming none Shrinkage of the emulsion.

Thus, as shown in FIG. 4, a polychromatic reconstructive light beam 41 can expand with a wide Range of existing wavelengths used to

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to successfully reconstruct a color image 43 of the subject scene 35 from a hologram 31 *. The reconstructing light beam 41 should and will be similar or identical to the reference beam 33 used in the construction of the hologram preferably obtained from a substantially point-shaped white light source 45. Points of image 43 will be so sharp like the ability of any diffraction pattern produced within the volume of the emulsion of the hologram 31 to be a narrow band of To transmit colors (wavelengths) of the reconstructing beam 41. A separate image is made of each of the different Diffraction patterns are generated which, when superimposed, produce the multicolored three-dimensional image 43.

One might think that since the two techniques of the focused image and the backbeam holography are each chromatic Reduce scatter in several ways when using a polychromatic reconstructive radiation source there would be no further advantage in a process that basically combines these two techniques. However, it was discovered that a color image with further improved sharpness from a hologram created by the combination of these two techniques is generated, can be reconstructed.

A specific arrangement for the construction of an improved hologram according to the present invention results 5, in which a sheet of photographic film 47 is on one side through a focused image 49 of a subject scene 51 is illuminated. The photographic film 47 is on its opposite side by one, a plurality of individual coherent wavelengths containing reference beam 53 illuminated. An article bundle 55 contains the same individual ones coherent wavelengths as the reference beam 55, and both beams are, generally speaking, from the same source or

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the same sources. The article 51 influences the article bundle 55 to produce a modified one from the article Bundle of objects 57 deposited on or near the photographic film by some optical system such as for example a lens 59, is imaged.

When reconstructing a color image with improved The hologram, as in FIG. 6, becomes sharpness of a hologram 47 * constructed according to the improved technique of FIG shown with a polychromatic reconstructive light beam 61 illuminated, which is similar or identical to the reference beam 53. Any of a variety of dot or apparent Point sources of 63 white light can be used. The result is a color image 65 of the subject scene 51, which is seen by the observer in a reflecting light beam 67, which has a degree of sharpness that is opposite to that of the focused image method or the backlighting method ? _i ^ in generated images 29 and 43 is improved.

FIGS. 7 and 8 provide an explanation for the improved sharpness of the images reconstructed with polychromatic light by the techniques according to the invention. FIG. 1 illustrates, on an enlarged scale, a fragment of the hologram 31 * which was constructed according to the backlighting technique as illustrated in FIG. 3. When a single point of the subject scene is viewed, part of a reconstructing polychromatic light bundle 69 illuminates the hologram 31 * in order to reconstruct an image of the point to be examined. Since a color hologram constructed by backlighting methods contains an individual diffraction pattern for each wavelength used during the construction of the hologram 31 *, let us first consider the effect of a single diffraction pattern in the reconstruction of an image of the point in question.

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tes considered. Such a single diffraction pattern diffracts a band of wavelengths (color spread) of the incident polychromatic light bundle 69 around the wavelength used to construct the hologram of approximately 50 to 100 angstroms bandwidth, depending on the thickness of the photographic emulsion and the construction geometry used. Since the hologram forming diffraction pattern is a beam stop in a manner dependent on its wavelength extent, a transmitted light from a single diffraction pattern wave Ä is bad bent over a range of angles, resulting in a blurred image of the examined dot subject scene = The light beam 71 with The shortest wavelength within the transmitted range would be diffracted at the largest angle to form a virtual image 37 of the examined point, and the longer wavelength light beam 75 would be diffracted at a wider angle to produce an image 77 of the same point . Between these two images there will be the other images 79, 81 and 83 of the point, which are reconstructed by light rays with wavelengths between the wavelengths of the light rays 71 and 75. It would be preferable, w => nn would limit the diffracted light on a single wavelength, but what can not be achieved as long as the Ho (logramm is illuminated with white light _o The result is a blurred image of the point, which is the observer each other diffraction pattern recorded in the hologram 31 'diffracts other wavelength bands to produce a plurality of images of the point under consideration, resulting in a composite blurred multicolored image of the point.

Reconstruction of an image of the same point in the subject scene is illustrated in Fig. 8, in which a different

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enlarged portion of the according to the techniques of this invention constructed holograms 47 * is illuminated with the same polychromatic illumination 69 as in FIG. 7. Each diffraction pattern within the film emulsion diffracts a band of wavelengths of the polychromatic light beam 69 to the wavelength used to construct the particular diffraction pattern around as with the ordinary backlit hologram of Fig. 7. However, since the image is now being constructed during the construction of the When the hologram is focused in the photographic film, the same band of diffracted wavelengths becomes a sharper image of one reconstruct the given point of the object because the image is reconstructed at a point closer to the hologram than in the usual backlit hologram of FIG. 7. In the arrangement illustrated in FIG. 8, the observer sees an overall image of the object point which is a sum of the images reconstructed by each diffracted wavelength, such as images 85 and 87, this overall image being smaller and thus more similar to the actual point of interest. All diffraction patterns within the film emulsion reconstruct a sharper one Buddies point in its particular waveband under generation a color image of the point with improved sharpness.

The improved technology according to the invention is based on the recognized principle that a diffraction pattern in a Hologram bends light rays at an angle that depends on the wavelength and that this creates chromatic scattering, when a range of wavelengths is dispersed. The backlit holographic technique is used to make the tape diffracted by a reconstructing white light source Restrict wavelengths and thereby chromatic scattering. The holographic technique of the focused image is thus combined to further reduce chromatic scattering by reducing the distance covered by the band of diffracted wavelengths

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must travel from the hologram until it is focused as an image. It was discovered that both techniques can help reduce chromatic scattering act cumulatively and thus improve the sharpness of the image.

The use of various optical systems and light sources is offered to those skilled in the field of holography for the construction of a hologram according to the invention in accordance with the technology, as is illustrated in FIG. A krypton laser can be used to generate both the drawing bundle 53 and the article bundle 55 with a suitable optical system. Kin Krypton laser gives a power that contains the usable lines of 6471 Å (red) 5208 K (green), and 4662 Å (blue). The red and green lines are preferably used for a two-color hologram according to the invention, as is described with reference to FIG. In the reconstruction, any good point light source is used to reconstruct an image in accordance with the arrangement of FIG. 6. A small incandescent lamp, for example, supplies appropriate polychromatic light for viewing the recorded image. The flexibility that is given for the reconstruction of full color images is an advantage of the invention.

When processing the film exposed according to the inventive techniques, the photographic emulsion must im are generally swollen to compensate for the shrinkage that occurs in the development process. This is a problem with all backlit holograms, where the thickness of the emulsion partly determines the wavelength ranges that are allowed through will. The usual swelling techniques used by the professionals are known in the holographic field, such as can be used with any other backbeam hologram.

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The exemplary embodiment of the construction of a Holograms by means of the inventive 'with reference Techniques described on Fig. 5 shows the use of a lens 59 to capture an image of the subject scene in or near the to place the photographic plane. It should be noted that any standard optical system has many variations for effecting this mapping can be used. Holographic Techniques can also be used to depict a scene of objects in photographic film, as is done for such Techniques illustrated in FIG. 9. A master color hologram 89 is made according to the basic one in the foregoing and in the already mentioned application P 14 72 071.9 and its excretions described technology constructed what to a sharp reconstructed image. A multicolored real image 59 is formed from the hologram 89 by means of coherent beams 91 and 92 are reconstructed with specific wavelengths (colors), these wavelengths being converted into an image-bearing beam 93 be bowed. These reconstructing bundles are aligned with respect to the hologram in exactly the same way as the corresponding ones Reference beams of the same wavelength were aligned. If more than two different wavelengths for construction of the hologram 89 are used, corresponding additional reconstructing bundles must be present.

The image-bearing diffracted bundle 93 impinges on one side of the photographic film 97 while a draw bundle 99 is directed against the opposite side of the film 97, to construct a hologram 97 * according to the invention. The reference beam 99 must have a number of different wavelengths which are coherent with the reconstructing bundles 91 and 92.

If the hologram 97 * of FIG. 10 with a polychromatic reconstructing bundle 101 is illuminated, so

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an image 103 is reconstructed in color with a sharpness which is improved compared to one with white light illuminated only focused image hologram or an only backlit hologram. The reconstructing bundle 101 is generated by any convenient, essentially punctiform white light source 105 and should approximate that of the Reference bundle 99 have opposite curvature.

Other good color quality holographic techniques can be used to construct a master hologram 89. For example, a backlit hologram constructed in accordance with FIG. 3 can be used if it is provided with a single light beam is reconstructed, the curvature and wavelength content of which is similar or equal to that of the construction of the hologram used reference beam 33.

It will be appreciated that the invention can be practiced with a number of specific designs or arrangements of the optical elements and with other variations can. The principles of the invention as taught herein can be used even for holography, the other types of radiation are used, such as electromagnetic wave energy outside the visible range, or with pressure wave energy. Furthermore, a number of different types of holographic detectors are available, the photosensitive material of a photographic film like him is explained in the foregoing and assumed in the drawing, represents only one of these types.

Expectations

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Claims (10)

DA-K511 - 16 - * Claims 'Ij method for the construction of a hologramity that is suitable for the reconstruction of a color image of an object scene, marked. through the steps: Illuminating a scene of objects with a bundle of objects coherent radiation containing at least two distinct or different coherent wavelengths; Imaging the illuminated object scene onto a side of a detector; and Illuminate the detector from an opposite one Side of the same with reference radiation that contains at least two specific or different wavelengths, each of which is wavelength is coherent with a wavelength component of the object bundle. creating a hologram that appears to be three-dimensional Reconstruct color image. 2. The method according to claim 1, characterized in that for illuminating the detector with reference radiation at least two specific or different wavelengths on the detector in a single beam from a common source position be agreed. 009825/12 53 DA-K511 - 17 - 3. Method of reconstructing a color image of an object scene of a hologram constructed according to claim 1 or 2, characterized by the further one Step of illuminating the hologram with incoherent multi-wavelength 3t payment. 4. The method according to claim 3, characterized by illuminating the hologram from a single source position. 5. Method of reconstructing a color image of an object scene, according to claim 3 or 4, characterized in that the step of illuminating the hologram with radiation the illumination of the hologram with polychromatic electromagnetic radiation within the visible Spectrum includes. 6. A method of constructing a hologram capable of reconstructing a color image according to claim 1, characterized in that characterized in that the step of imaging the illuminated subject scene onto a side of the detector additionally comprises the step of reconstructing the image from a color hologram. 009825/1253 7. A method of constructing a hologram suitable for reconstructing a color image according to claim 1 or 2, thereby characterized in that the step of lighting the subject scene illuminates the subject scene with electromagnetic radiation within the visible spectrum and the step of imaging the illuminated object the illustration of the object scene on one side of a photosensitive sheet. 8. Device for performing the method according to one of the preceding claims, marked by chnet a source of a bundle of rays (33,37 or 53,55) each containing at least two coherent wavelengths and through an input -authority to hold a detector (31 or 47) between the Light source and an object to be imaged (35 or 51). 9. Device for the reconstruction of a device according to one of the claims 1 to 6 or hologram constructed with the device according to claim 7, characterized in that a source (45 or 63) of two specific or different wavelengths on one side of a device for holding the Holograms (31 * or 47 ') is arranged. 10. Device according to claim 6, characterized in that between the detector (47) on the side of the ab-. forming object (51) a lens system, (59) is arranged. 009825/1253