DE2025617A1 - Process for converting absorption holograms into phase holograms - Google Patents

Description

Process for converting absorption holograms into phase holograms

The invention "relates to methods for converting absorption holograms, their interference structure by reduction of exposed silver salts in a photographic development process have been generated into a phase hologram.

Absorption holograms are usually by holographic exposure of photographic materials with at least one Silver halide emulsion layer and subsequent photographic processing prepared.

The overall advantage is the high sensitivity to light Spectral range of silver halide emulsions. Absorption holograms. are disadvantageous because of their relatively low diffraction efficiency. Diffraction efficiency is the intensity ratio of incident light to that through the Hologram in the reconstruction into a first diffraction order understood diffracted light. The diffraction efficiency is

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in the case of absorption holograms only a few percent. In practice, values in the range from 0.5 to 3% are achieved.

To increase the diffraction efficiency, the absorption holograms are converted into phase holograms by removing the silver image by conventional bleaching. Phase holograms with diffraction efficiencies of about 10-30 % are obtained. With regard to the diffraction efficiency, a considerable improvement is achieved; however, the photographic quality of the hologram is deteriorated upon bleaching. The holograms produced in this way generally show a disruptive light scattering, which leads to a blurring of the reconstructed image. It should also be considered that some of the bleach baths currently in use rely on the re-halogenation of silver. The resulting phase holograms are therefore light-sensitive and darken, which leads to a decrease in the diffraction efficiency.

It is also known to produce phase holograms directly by holographic exposure of photo-crosslinking layers, e.g. Chromate gelatin layers. In this way it is possible to produce phase holograms with high diffraction efficiencies and good photographic quality of the reconstructed images. However, the practical importance of these methods is due to the low light sensitivity of the photocrosslinking layers limited.

The invention is based on the task of producing methods of phase holograms with high diffraction efficiency and negligible light scattering using to develop photographic materials with high photosensitivity.

It became a method of making phase holograms developed by converting absorption holograms, the absorption hologram being copied holographically onto a layer whose refractive index can be changed by exposure.

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ORIGINAt INSPECTED

The absorption holograms that are assumed to be produced in a known manner. Of primary importance are absorption holograms, their information-carrying structure metallic silver and which are produced in a known manner by holographic exposure of silver halide emulsions will.

As holographic, light-sensitive copying materials, the refractive index of which changes upon exposure, are primarily suitable Line of photocrosslinking layers, preferably chromate gelatin layers.

The absorption hologram is expediently located during the copying process and the photosensitive material for manufacture of the phase hologram in contact with each other.

According to an extension of the method according to the invention, the absorption hologram is composed of several in one Layer superposed partial holograms together. Two practically interesting cases come into consideration here. Either all partial holograms have the same mean spatial frequency and only differ from one another by their spatial orientation, or all partial holograms have the same spatial orientation and only differ by their mean spatial frequency from each other. In any case, however, the copying process runs in such a way that each partial hologram for in compliance with the Bragg condition on the photocrosslinkable Layer is copied.

According to a development of the method according to the invention it is provided that the absorption hologram in one three-dimensional storage medium, the copied holograms, however, in a three-dimensional or two-dimensional storage medium be generated.

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An alternative embodiment of the method according to the invention is characterized in that during the copying process on the Side of the copy material that faces away from the absorption hologram and the laser source, a mirror arranged in contact is, wherein in the photosensitive layer of the copying material both two transmission phase holograms and two reflection phase holograms are generated.

In a further embodiment of the method according to the invention is used by the laser light source during the copying process and the layer side facing away from the absorption hologram into the light-sensitive layer of the copying material external reference beam introduced, being in the copy layer both a transmission phase hologram and a Reflection phase hologram is generated.

The method according to the invention will now be described in more detail with reference to drawings and exemplary embodiments. Show it:

Figure 1

the easiest way to carry out the copying process

Figure 2

an embodiment of the method in which an absorption-transmission hologram several phase transmission holograms in the light-sensitive layer of the copy material at the same time and phase reflection holograms are produced

Figure 3

an embodiment in which an absorption-transmission hologram only one phase transmission hologram at a time in the light-sensitive layer of the copying material and generating a phase reflection hologram.

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According to Figure 1 ernäli; one from which serve as the original absorption-transmission hologram a phase transmission hologram. Transmiss! onshologram means that reconstruction takes place in transmission. The principle of this embodiment of the method according to the invention is shown schematically in FIG.

In FIG. 1, -1 denotes the laser light source. As template an absorption hologram is used with the information-carrying layer 2, arranged on the layer carrier 3. The interference surfaces 9 in the absorption hologram are indicated by the hatched lines indicated. Of the. Distance between two neighboring interference surfaces is small compared to the thickness of the information-carrying layer, so that a three-dimensional interference structure is present. The copying material consists of the light-sensitive layer 4 on the layer carrier 5. Here too, the at Copying process generated interference surfaces indicated as hatched lines 10 in the layer 4. It goes without saying it in this embodiment of the method according to the invention also possible, the light-sensitive layer of the copying material during the copying process with the information-carrying layer of the Bringing Originals into direct contact. From the laser light source 1 the light beam 6 goes out. In the layer of the original that contains the absorption hologram, part of the incident light in the zeroth order as a reference beam 7 straight through the copy material, another part is preferably in a first order at the interference surfaces of the absorption grating if the Bragg condition is observed bent. This light is optimally diffracted into a 1st order indicated by the ray 8 and is often referred to in holography as the object ray. By interference of the reference beam 7 and the diffracted beam 8 arise in the light-sensitive Layer the copy material in the direction of the bisector 11 between these rays the interference surfaces 10. The interference surfaces 10 agree in terms of spatial orientation and distance (spatial frequency) with the interference surfaces 9 match.

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For the sake of simplicity, refraction effects are shown in FIG Entry of the light rays into the substrate and layers occur neglected.

Vie further described below in the specific examples in detail, the method according to the invention, the diffraction efficiency by a factor improved in this embodiment, that is, from an absorption hologram having a diffraction efficiency of 1 or 2%, a phase hologram having a diffraction efficiency of 30 or .60 # received. With regard to light scattering, the quality of the original hologram is fully preserved. There are two main reasons for these extraordinarily surprising results. On the one hand, an absorption hologram produced with the correct optical density D allows the chromate gelatin layer or other photo-crosslinking layers to be optimally controlled during the copying process of the type described. On the other hand, the quasi-grain-free structure of the chromate gelatin layer and the nature of the process mean that no additional light scattering occurs during the copying process, as is the case with the bleaching of absorption holograms. With regard to the optimal control of the copy material, we consider the following numerical example: The absorption hologram may have an optical density D = 1.0, which corresponds to an intensity transmission Tj = 10 ~ "= 0.1, i.e. 10%. Experience has shown that such an optical density An absorption hologram can be produced with a diffraction efficiency of up to 3.3 % . Thus, with the Bragg angle arrangement of the absorption hologram between the undiffracted and the diffracted beam, an intensity ratio of 3: 1 results, which is to be regarded as approximately optimal when copying absorption holograms onto chromate gelatin layers Strictly speaking, due to the extremely high dynamic range of the chromate gelatin, it is more favorable to set the optical density of the absorption hologram a little above D = 1, since the diffraction efficiency only decreases slowly with increasing D after reaching a maximum value (for B «0.6). With the

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ORfGJNAL INSPECTED

given intensity ratio between the undeflected and the A chromate gelatin can be applied to the diffracted beam control optimally, provided that sufficiently long exposure times are guaranteed.

In the embodiment described, a three-dimensional Absorption hologram on a two-dimensional photocrosslinking Layer to be copied. Such a two-dimensional photocrosslinking layer is present, for example, when Shipley AZ 1350 Photoresist is applied to a substrate in a thickness of about 1 / µm. Instead of the interference surfaces in one three-dimensional copying medium, one now has to do with interference lines in a copying medium, its layer thickness in the order of magnitude of the distance between two adjacent interference lines lies. The maximum possible diffraction efficiency of such two-dimensional phase gratings in a 1st diffraction order is known to be 34 #. With this extension of the Embodiments of the method according to the invention are mithia not quite as high increases in diffraction efficiency can be achieved as when copying onto a three-dimensional photo-crosslinking one Layer.

In a second embodiment of the method according to the invention are made from an absorption-transmission hologram at the same time in the light-sensitive layer of the copying material several phase transmission holograms and phase reflection holograms produced.

This embodiment is shown schematically in FIG. With regard to the formation, FIG. 2 corresponds to that caused by the hatching 10 in the light-sensitive layer 4 of the copying material indicated interference surfaces of the transmission grating of Figure 1. Here too, the emanates from the laser light source outgoing beam 6 partly as undiffracted beam 7 and partly as diffracted beam 8 into the copying material. In the light

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The sensitive layer of the copy material is caused by interference of these rays in the direction of the bisector, the interference surfaces 10. The interference surfaces 10 are correct. according to spatial orientation and according to distance (spatial frequency) with the interference surfaces 9 of the absorption transmission grating over.

This embodiment of the method according to the invention differs from that shown in FIG. 1 by the mirrors 12, which is in contact with the copy material. At this mirror, the beam 7 passing through undeflected is as new reference beam 14 is reflected. The beam 14 interferes with the diffracted beam 8. This occurs in the direction of the bisector 15 a reflection phase grating in the photosensitive Layer of the copy material, which is indicated by the hatching 13 in this layer. One denotes a grating as a reflection grating, if the information stored in it is reconstructed in reflection »The reflection phase grating 13 generally has a higher spatial frequency than the transmission phase grating 10, since between the beams and 14 (taking their direction into account) there is a larger angle than between rays 7 and 8.

The previous consideration of Eigur 2 is incomplete in this respect, than at the mirror not only the undiffracted beam 7 (reference beam) j but also the diffracted beam 8 (object beam) - in the copy material is reflected back »by interference of this reflected back object beam 8 with the reference beams H and 7 thus become in the photosensitive layer Another transmission phase grating for each of the opaque material and reflection phase gratings stored, which- differ from the previous ones The grids 10 and 13 discussed and indicated in FIG. 2 are distinguished primarily by their spatial orientation -, - From For the sake of clarity, these additional fritters are not included in FIG. Trouble-free recovery the information from each of the four by copying

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Existing holograms are achieved by means of a laser light source in compliance with the Bragg condition. A recovery of the information from the two reflection phase holograms by means of White light source (flashlight, sun) leads to disruptive color dispersions, since both holograms are approximately in the same spatial frequency range. To this for many practical uses Avoiding harmful restriction is now based on 3 describes a third embodiment of the method according to the invention. In doing so, an absorption-transmission hologram only one phase transmission hologram at a time in the light-sensitive layer of the copying material and generates a phase reflection hologram.

The! Figure 3 corresponds to the emergence of the Visual affinity 10 in the photosensitive layer 4 of the copying material indicated interference surfaces of the transmission grating of Figure 1. Here too, the emanates from the laser light source 1 outgoing beam 6 partly as undiffracted beam 7 and partly as diffracted beam 8 into the copy material. In the light-sensitive layer of the copying material by interference of these rays in the direction of the bisector 11, the interference surfaces 10. The interference surfaces 10 vote according to spatial orientation and spatial frequency with the interference surfaces 9 of the absorption transmission grating over.

This embodiment of the method according to the invention differs from that shown in FIG. 1 by the second reference beam 12, which enters the light-sensitive layer of the copying material from the side facing away from the laser light source 1. The reference beam 12 is derived externally from the light of the laser light source 1 by beam splitting. The reference beam 12 interferes with the diffracted beam 8. This creates a reflection in the light-sensitive layer of the copying material in the direction of the bisector 14.

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Phase grating 13. The information can be recovered from this reflection phase grating by means of a white light source without a disruptive color dispersion being observed. In the arrangement of Figure 3, a basic advantage of the arrangement of Figure 1 is retained, namely that the full intensity of the object beam 8 in the light-sensitive © layer of the
Copy material enters »Also is in the arrangement of
FIG. 3 the intensity of the external reference beam 12 can be set independently of the intensity of the object beam 8.
With regard to the reflection phase grating 13, the arrangement of FIG. 3 is unique compared to the arrangement of FIG
Disadvantage that due to the external reference beam 12 of the
mechanical stability of the overall arrangement, increased attention must be paid.

The absorption holograms from which the method according to the invention is based, in particular those ₉ thereof. Interferent structure consists of metallic silver, 'are - as already indicated above - in a known manner by holographic exposure
conventional photographic materials with at least
made of a silver halide emulsion layer »

Extremely fine-grained ₉ high-resolution ones are particularly suitable
Silberhlogenid-Emulsionsschichtexi, as they are S ₀ B ₀ by the company AGFA-GEVAIRT under the name SCIMTJA-Haterialiem on the market »

As a copy material for the production of the Plsaseniiolograiime one can practically. Each of the "known light-sensitive materialism with a photocrosslinkable layer v-srweaäejio There are negative-working layers, ie those ₉ that crosslink at the exposed areas and whose unexposed parts of the layer remain soluble in certain solvents ^ as well as positive-working layers, ie those that are on the Both photopolymerizing and photocrosslinking or photodimerizing systems are suitable.

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Reference is made in particular to polymers, preferably polyvinyl alcohol or copolymers thereof which contain vinyl alcohol units in polymerized form, which are in side chains Contain light-sensitive cinnamic acid groups or azide groups. Such polymers are described, for example, in the German Patents 1,099,732, 1,067,219, 1,063,802 or den American patents 1 965 710, 1 973 493, 2 063 348 or 2 566 302. A summary of photosensitive Polymers with cinnamic acid ester groups are found in the article by I. M. Minsk et al in J. Appl. Polymer Sc. 2 (1950) 302. Photosensitive systems with azide groups are described in German patents 1,053,782, 1,079,949, 1,079,950, 1,285,306 or French patent 1,455,154.

Light-sensitive Ohromat gelatin layers are also suitable sensitized in a known manner by treating gelatin layers with alkali metal or ammonium bichromate solutions will.

The method according to the invention also leads to phase holograms excellent photograph! see properties. 3) ie from the Images reconstructed with holograms are extremely sharp and, in the case of noise-free original holograms, are also noise-free. Depending on the quality and the mean optical density D of the absorption hologram, which is assumed in the copying process, the diffraction efficiency of the phase hologram obtained is between 30 and 80 #.

As a particular simplification, the method according to the invention has an effect that is inherently a disadvantage of Consider halogen silver absorption holograms 1st .. In the photographic processing of holographically exposed Silver halide emulsions shrink the layer due to the " Removal of the unexposed halogen silver, this layer-

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Shrinkage had to be corrected by swelling in order to while maintaining the object beam reference beam angle with the same light wavelength to be able to reconstruct which was used when the hologram was recorded. The swelling process can be omitted »if the reconstruction is carried out with shorter-wave light, i.e. green or blue laser light. This This circumstance fits particularly well into the process scheme according to the invention good, since the photocrosslinking layers used for the production of the phase hologram are preferably blue and are sensitive to green, so that swelling of the absorption hologram is not required. The layer shrinkage is due to a swelling hardening bath described below the chromate gelatin layer in the context of the invention Process schemes are practically negligible.

Example 1 (copying process according to Figure 1)

Production of the absorption hologram:

A photographic material is used, consisting of a silver bromide _{iodide gelatin layer with 3 5} 8 mol- ^ iodide content and an average grain size of 0.05 μm and a narrow grain size distribution.

The mean square spread of the size distribution is t <^ ~> 0.03 / µm. The packing density is above 0 ₅ 3 g of silver per egg ³ , the layer is panchromatically sensitive.

Commercially available photo plates of the type AGFA-GEVAER, for example, are suitable! SGIMTIA 8E75, & S56 ₉ 1OE75, 1OE56.

In such hole-dissolving halogen silver emulsion layers the hologram structure is caused by interference from an object ■ incoming and an unmodulated reference bundle generated «, '-

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Since both bundles of rays have to be coherent with each other, even with larger path length differences, they are expediently taken from a laser via a beam splitter, continuous krypton and argon lasers are particularly suitable, which optionally emit different colors in the visible and ultraviolet spectral region with high intensity. _{For example, the ^ 1} = 647 nm line of the krypton laser is very useful for generating the absorption hologram discussed in an AGEA-GEVAERT SCIMTIA 8E75 photo layer.

The exposed photographic material is developed in a developer of the following composition

Hydroquinone 3.5 g p-methylaminophenol 7.5 g KBr 3.0 g Na ₂ SO ₅ 40.0 g Na ₂ CO, 30.0 g H "0 1000 ml

and then fixed with a sodium thiosulfate solution.

Production of a copied transmission phase hologram:

A weakly hardened 20y-µm thick clear G-ela tine layer that is arranged on a glass plate, is treated for 5 minutes with a 7 $ aqueous solution of Ammonium dichromate sensitized at room temperature. The material is then dried in the dark.

The copy exposure takes place according to the arrangement specified in Elgur 1. A real image of the holo-

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graphed object and made an optimal Bragg angle adjustment based on the image brightness. Then the copy material is brought into contact with the adjusted absorption hologram and the copy material is exposed through the absorption hologram with the fanned out laser beam. Depending on the type of copy material, the laser light wavelength and intensity as well as the optical density D of the absorption hologram, there are considerable differences in the copy times. For example, for chromate gelatin, for a laser light wavelength X = 520 m, for a laser light output I = 100 mW, for an optical density of the absorptive hologram D is obtained

2 = 1 and a copying time of 15 minutes for a hologram area of 100 cm. By using a powerful argon laser and copy at shorter wavelengths are the copy times can be reduced considerably.

The Funktionsprinsip described chromate gelatin layers based on the fact that the swelling capacity of the gelatin with increasing light absorption as a result of cross-linking decreases "" B _e i the chromate gelatin interference surfaces are thus related to structures, resulting from an exposure hardening of the gelatin. In order to manage with the lowest possible exposure energies, the exposure is followed by water swelling, which takes place primarily in the unexposed areas of the layer and at the same time causes desensitization. In order to achieve the greatest possible differences in the Br ecaungs index between the hologram structure and the unexposed parts of the layer, rapid dehydration is then carried out, for example using a short isopropanol bath and subsequent drying. It is observed, however, that the gelatin dissolves partially or completely in the soaking time necessary for desensitization, so that further hardening which takes place at the same time is necessary. This hardening is also necessary for the later

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rapid dehydration to prevent the gelatin from becoming cloudy. We have the swelling and hardening required in one single process step and achieved with the greatest success that we treated the exposed layer for 15 minutes with a 10% ghromalum solution. This was followed by the Rinse in a water bath for 30 minutes. Formed the conclusion again the rapid dehydration and subsequent drying. The layers thus obtained are in natural Light as clear as window glass, can be used without any change

-2 ·

Laser light outputs up to 1 who are applied and have an unlimited shelf life.

In the literature, L.H. Lin, Appl. Optics Vol. 8, No. 5, May 1969, pp. 963-966, describes another possibility for swelling hardening of chromate gelatin layers. And that is here After exposure, the chromate gelatin layer is again placed in a 0.5 T ammonium dichromate solution for 5 minutes, whereby the layer also absorbs hexavalent chromium ions. All 6-valent chromium ions are then in another Kodak Rapid Fixer Bath (with additional hardener) reduced to trivalent chromium ions, which are apparently the most important Cause part of the hardening. This is in turn followed by rapid dehydration and drying.

Despite the chemical similarity of the two highlighted here In swelling hardening processes we see a difference in that the Lin * process see the effect of a slight swelling of the finished processed material results, while in our swelling hardening process we have a slight shrinkage of the finished processed Observe materials, ./we make this difference back to the fact that our process causes a more pronounced hardening, which also explains the excellent stability of our layers.

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The Absorptionsholograimn we use in the copying process of Figure 1 had had a diffraction efficiency of about 3% · Pas at your copying phase hologram obtained a diffraction swirkungsgrad of 80 io with excellent quality of the reconstructed image.

Example 2 (copying process according to Figure 2) Production of the Absorptionßiiolograms:

The production of the absorption hologram takes place in the same pasture as 3ie _; in Example 1 has been described. The Bragg adjustment of the absorption hologram before the copy is also carried out in the same way as described in Example 1.

Production of two copied transmission and reflection phase holograms each in one shift:

The sensitization and subsequent processing of the C _n Romat gelatin copy material is carried out in the same manner as described in Example. 1 The difference between Example 2 and Example 1 lies in the optical copier arrangement. According to FIG. 2, the optical copier arrangement is now supplemented by the mirror 12. As explained earlier, the mirror reflection of the unbroken beam 7, the diffracted beam 8 and the mutual interference of the different beams lead to the storage of two transmission and two reflection phase gratings in the copy layer. The mirror reflection has the effect that, with regard to the relative intensities of the interfering rays, similarly favorable values are obtained as were given in Example 1 for the copied transmission phase hologram. With an optical density D = 1 of the absorption hologram, the chromate gelatin layer is thus approximately optimally controlled for all four copying holograms, with the large dynamic range. this layer plays an essential role. The considerations in Example 1 apply to the copying time.

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The absorption hologram used by us in the copying process according to FIG. 1 had a diffraction efficiency of about 3 i>. The transmission phase holograms obtained in the copying process had a diffraction efficiency of 60 <$>. As a result of the correlation between them and discussed earlier, the reflection phase holograms are characterized by considerable color dispersion, which makes reconstruction with monochrome laser light necessary.

Example 3 (copying process according to Figure 3) Production of the absorption hologram:

The production of the absorption hologram proceeds in the same way Manner as described in Example 1. The Bragg adjustment of the absorption hologram before the copy is also carried out in made in the same manner as described in Example 1.

Production of one copied transmission and one reflection phesenhologram each in one shift:

The sensitization and subsequent processing of the chromate-gelatin copying material takes place in the same manner as described in Example 1. The difference between that Example 3 and Example 1 are in the optical copier assembly. According to FIG. 3, the optical copier arrangement is now supplemented by an external reference beam 12. This reference beam 12 is thereby divided by the beam from the laser 1 outgoing light obtained. The beam splitter ratio is expediently variably adjustable. The fundamental difference between the arrangement of Figure 3 and the The arrangement of Figure 2 is that now a mirror reflection of the diffracted beam 8 is avoided. This comes about it in the copy material to store only one trans-

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AS

mission and reflection phase hologram. So that is the color dispersion switched off with the reflection hologram; a reconstruction with a white light source becomes possible. on the other hand remains in the arrangement of .Figur 4 the advantage of full utilization of the deflected beam 8 (the object beam) full obtain.

With regard to the relative intensities of the interfering beams, optimal settings are possible via the optical density D of the absorption hologram and via the splitting ratio V of the beam splitter discussed. Expediently, one again starts from an optical density D = 1 and a division ratio V = 0.1. In other words: the intensity of the reference beam 12 should be approximately 10 % of the intensity of the incident beam 6. With a diffraction efficiency of the absorption grating of 3 % , the intensity of the diffracted beam 8 is then approximately the third part of the reference beam 12, which is to be regarded as approximately optimal. Due to the optical density D = 1 of the absorption hologram, an intensity ratio of approximately 1: 3 also results for the rays 8 and 7 forming the copied transmission phase hologram. With regard to the copying time, the considerations of Example 1 apply again.

The absorption hologram used by us in the copying process according to FIG. 3 had a diffraction efficiency of about 3 %. The transmission phase hologram obtained during the copying process had a diffraction efficiency of 60 ^. The diffraction efficiency of the reflection hologram was found to be of a similar order of magnitude, the measurement being carried out with laser light. The quality of the reconstructed images was very good.

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INSPECTED

Claims (8)

Patent claims: /1. Process for the production of phase holograms by conversion of absorption holograms, the information-bearing structure of which consists of a material that emits light absorbed from the visible range of the spectrum, characterized in that the absorption hologram is holographic is copied onto a layer whose refractive index can be changed by exposure. 2. The method according to claim 1, characterized in that on a photocrosslinkable layer is copied. 3. The method according to claim 1, characterized in that on a chromate gelatin layer is copied. 4. The method according to claim 1, characterized in that the absorption hologram and d © 3 during the copying process the photosensitive material for making ä $ s Phase holograms are in contact. 5. The method according to claim 1 and 4 »characterized in that that the absorption hologram by holographic superposition of several partial holograms in the same Layer is generated, which is then successively copied into the copy medium in compliance with the Bragg condition will. 6. The method according to claim 1 and 4, characterized in that that the absorption hologram is in a three-dimensional storage medium, whereas the copied holograms are in one three-dimensional or two-dimensional storage medium can be generated. A- (J 612-19-109850/1466 ZD 7. The method according to claim 1 and 4, characterized in that during the copying process on the side of the copying material which faces away from the absorption hologram and the laser light source, a mirror is arranged in contact, wherein in the light-sensitive layer of the copying material both ζ // egg Transmission phase holograms as well as two reflection phase holograms are generated. 8. The method according to claim 1 and 4, characterized in that during the copying process in the photosensitive layer of the copy material an additional external reference beam is introduced, namely from that of the laser light source and the layer side facing away from the absorption hologram, with both a transmission phase hologram in the copying layer as well as a reflection phase hologram is generated. A-G 612 -20-1098S0 / U66