JP2009175217A - Method of manufacturing volume hologram and volume hologram prepared by the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a volume hologram superior in design properties and security properties by a simple method. <P>SOLUTION: In the method of manufacturing the volume hologram using a computer generated hologram obtained by recording amplitude information and phase information on a prescribed recording surface by computation using a computer, the computer generated hologram 1 includes a first direction X and a second direction Y perpendicular to the first direction X, includes parallax only in the first direction X, and includes respective unit areas B1, B2, B3, ..., Bm, ..., BM having a prescribed width in the second direction Y. Diffraction patterns with different spatial frequencies Cm1, Cm2, Cm3, ..., Cmt, ..., CmT in the second direction Y are formed in the respective unit areas B1, B2, B3, ..., Bm, ..., BM. A first reproduced image O' is reproduced by irradiating the computer generated hologram 1 with first reproduction illumination light 2 to generate first diffraction light 3 from the computer generated hologram 1. The hologram H1 at the first stage is recorded by simultaneously introducing the first diffraction light 3 and first reference light 4 on a hologram recording material H1 at the first stage. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a volume hologram and a volume hologram produced by the method.

  2. Description of the Related Art Conventionally, it is known that a hologram is provided on a cash voucher or a credit card to prevent forgery. As this hologram, there is a computer-generated hologram (CGH) that is produced by forming interference fringes on a predetermined recording surface by calculation using a computer (see Patent Document 1).

JP 2001-013858 A JP 2000-214750 A JP 2002-72837 A JP 2005-215570 A A. W. Lohmann and D. P. Paris: "Binary Fraunhofer Holograms, Generated by Computer", Appl. Opt., 6, 10, pp. 1739-1748 (Oct. 1967) Wai Hon Lee: "Sampled Fourier Transform Hologram Generated by Computer", Appl. Opt., 9, 3, pp. 639-643 (Mar. 1970)

  However, the conventional computer-generated holograms proposed so far are holograms that are excellent in design and security, but are relief-type holograms that are more easily forged and more secure than volume-type holograms. There are inferior parts in terms of.

  The present invention has been made in view of such problems of the prior art, and the object thereof is a method for producing a volume hologram that is excellent in design and security by a simple method and a volume produced by the method. Is to provide a type hologram.

  The present invention that achieves the above object provides a method for producing a volume hologram using a computer-generated hologram formed by recording amplitude information and phase information on a predetermined recording surface by an operation using a computer. Each unit region having a first direction and a second direction orthogonal to the first direction, having parallax only in the first direction, and having a predetermined width in the second direction, A diffraction pattern having a different spatial frequency in the second direction is produced in each unit region, and the computer-generated hologram is irradiated with a first reproduction illumination light to generate a first diffracted light from the computer-generated hologram. A reconstructed image is reproduced, and the first diffracted light and the first reference light are simultaneously incident on the first-stage hologram recording material to record a reflection-type or transmission-type first-stage hologram.

  In addition, the second reproduction illumination light is irradiated to the first stage hologram to generate second diffracted light from the first stage hologram to reproduce the second reproduction image, which is arranged in the vicinity of the second reproduction image. The second diffracted light and the second reference light are simultaneously incident on a second-stage hologram recording material, and the second-stage hologram is recorded as a reflective or transmissive volume hologram.

  In addition, the spatial frequency of the diffraction pattern gradually changes from one to the other within the unit region.

  The recording is performed using object light that spreads in a first direction from a point light source set on a recording object and spreads in a second direction from a position different from the point light source.

  Further, a predetermined light beam that is spread from the linear light source set on the recording object in the first direction and that has a constant width in the second direction and that is defined for each unit region in the second direction as the reference light. It is recorded using a reference beam that is focused on a position.

  Further, the diffraction pattern is characterized by comprising interference fringes.

  The diffraction pattern may be a pattern that modulates phase and amplitude.

  Furthermore, the volume hologram is manufactured by the volume hologram manufacturing method.

  According to the present invention, a computer-generated hologram having a parallax only in the first direction and having a different spatial frequency of the diffraction pattern in the second direction in the unit region and expanding the viewing area in the second direction Since the volume hologram is manufactured using the holographic lens, the diffusion angle of the diffracted light can be changed without using a lenticular lens or a uniaxial diffusing plate as in the prior art, and the volume hologram with an enlarged viewing area in the second direction is obtained. be able to.

  Hereinafter, a method for producing a hologram of the present embodiment will be described with reference to the drawings.

  In this embodiment, first, the computer-generated hologram 1 is produced. 1 to 3 show a basic method for producing the computer-generated hologram 1.

  First, in the present embodiment, a computer-generated hologram that is recorded using object light that spreads only in a predetermined one-dimensional direction from a point light source set on an original image is used. This manufacturing method is a method based on the description in Patent Document 1. That is, as shown in FIG. 1, when object light Oi emitted from an arbitrary point light source Pi on the original image O spreads only in the horizontal direction (in a plane parallel to the XZ plane) in the present embodiment as shown. Assume. Then, the object light Oi reaches only the linear region B on the recording medium 1, and the object light Oi does not reach any other region of the recording medium 1. In the case of producing a hologram by an optical method, it is extremely difficult to limit the spread of object light in this way. However, if a hologram is produced using a computer, the object can be simply modified by correcting the arithmetic expression. Light can be easily controlled. Therefore, the same limitation is imposed on the object light emitted from all point light sources constituting the original image O (the limitation that the object light spreads only in a plane parallel to the XZ plane). The computer generated hologram produced in this embodiment is a computer synthesized hologram having only horizontal parallax.

  FIG. 2 is a perspective view showing a specific example of a recording method based on the basic concept described above. In this example, the original image O and the recording medium 1 (recording surface) are each divided in the horizontal direction by a large number of parallel planes to define a large number of linear unit areas. That is, as shown in the figure, the original image O is divided into a total of M unit areas A1, A2, A3,..., Am,... AM, and the recording medium 1 similarly has a total of M unit areas B1, B2. , B3,..., Bm,. When the original image O is a stereoscopic image, each of the unit areas A1, A2, A3,..., Am, ... AM is an area obtained by dividing this stereoscopic surface portion. Here, the M unit areas on the original image O and the M unit areas on the recording medium 1 have a one-to-one correspondence. For example, the mth unit area Am on the original image O corresponds to the mth unit area Bm on the recording medium 1.

  In the example shown in FIG. 2, the width of each unit area A1, A2, A3,..., Am,... AM is the Y direction as the second direction of the point light source defined on the original image O (this embodiment). It is set equal to the pitch in the vertical direction in the form, and each unit area is a linear area in which point light sources are arranged in a line. For example, in the illustrated example, N point light sources Pm1 to PmN are arranged in a line in the m-th unit region Am.

  Further, the width of each unit area B1, B2, B3,..., Bm,... BM is set equal to the pitch in the Y direction of the point light source defined on the original image O. The calculation point is a linear region arranged two-dimensionally. The illustrated calculation point Q (x, ym) indicates a calculation point located in the m-th unit region Bm, and is at a position indicated by a coordinate value (x, ym) in the XY coordinate system.

  In the case of this example, the interference wave intensity at the calculation point Q (x, ym) is obtained as follows. First, a unit area Am on the original image O corresponding to the unit area Bm to which the calculation point Q (x, ym) belongs is determined as a calculation target unit area. Then, the amplitude at the position of the calculation point Q (x, ym) for the interference wave formed by the object light Om1 to OmN emitted from the point light sources Pm1 to PmN and the reference light Lθm in the calculation target unit area Am. If the intensity is obtained, this amplitude intensity is the interference wave intensity at the target calculation point Q (x, ym). Here, the reference light Lθm is, for example, a monochromatic parallel light beam parallel to the YZ plane, and is incident on the recording medium 1 at the same angle at any position. Alternatively, the incident angle θm of the reference light Lθm is determined based on the setting of the virtual illumination and the virtual viewpoint assuming the observation environment. For example, when assuming a point light source from above at the time of observation, the unit region B1 at the upper end The incident angle θ1 of the reference light Lθ1 from the normal direction of the recording medium may be set to a small angle δ, and the incident angle θM of the reference light LθM to the lower unit region BM may be set to a large angle β. .

  FIG. 3 is a top view for explaining the concept of such arithmetic processing, and shows a state in which the original image O and the CGH original recording medium 1 shown in FIG. 2 are viewed from above. As shown in the figure, the object light necessary for obtaining the interference wave intensity at the calculation point Q (x, ym) is emitted from N point light sources Pm1,..., Pmi,. , Omi,..., OmN, and it is not necessary to consider object light from all point light sources constituting the original image O. In this way, if the predetermined interference wave intensity is obtained for each of the calculation points Q (x, ym) defined on the CGH original recording medium 1, the intensity distribution of the interference wave to be recorded on the CGH original recording medium 1 is obtained. If the intensity distribution of the obtained interference wave is physically recorded by some method, the CGH original plate 1 is obtained. Specifically, as described in Patent Document 2, the CGH original plate 1 can be produced by recording a rectangle having an occupation rate corresponding to the intensity of the interference wave at a position corresponding to the calculation point.

  As described above, with reference to FIGS. 1 to 3, the light source information on the m-th unit area Am defined on the original image O is the m-th unit defined on the CGH original recording medium 1. A method of recording on the area Bm has been described. In the model described in this method, each of the unit areas Am and Bm is an elongated strip-shaped area, and the point light sources are arranged one-dimensionally and the calculation points are arranged two-dimensionally.

  In the above method, the amplitude and phase of the object light at the calculation point Q on the divided area may be recorded in addition to the method of recording with interference fringes due to interference with the reference light as described above. As described in 3 and 4, the phase may be recorded by the depth of the groove of the three-dimensional cell having a groove on one surface, and the amplitude may be recorded by the width of the groove.

  Alternatively, as described in A.N. W. The amplitude and phase may be recorded by the Lohmann method, the Lee method described in Non-Patent Document 2, or the like.

  FIG. 4 is a diagram showing a configuration of the CGH original plate 1 of the present embodiment. 4A is a view of the system shown in FIG. 2 observed from the X direction as the first direction, and FIG. 4B is an enlarged view of the CGH original plate 1 observed from the X direction.

  The CGH master plate 1 of this embodiment is a diffraction pattern so that the pitch intervals (spatial frequencies) in the Y direction in the unit regions B1, B2, B3,..., BM shown in FIG. By producing the interference fringes, the viewing zone in the Y direction is changed. For example, the interference fringe spacings Cm1, Cm2, Cm3,..., CmT in the Y direction of the unit region Bm of the CGH original plate 1 can be produced in various patterns as shown in FIG. In FIG. 4 (b), the interference fringe spacings Cm1, Cm2, Cm3,..., CmT in the Y direction are illustrated as conceptual diagrams, but in many cases, the physical interference fringe pattern is formed on the surface of the CGH original plate 1. It is formed as unevenness. In this case, as shown in FIG. 5, there are various methods such as a rectangular cross section (FIG. 5A) and a curved line (FIG. 5B). In addition, the interference fringe interval can be determined not by changing the cross section but by periodically changing the two-dimensional pattern in the Y direction. In FIG. 5, the interference fringe intervals that differ in the Y-th direction gradually change from one to the other in the unit region. However, the present invention is not limited to this, and various patterns can be produced.

  FIG. 6 is a diagram illustrating a state when the CGH original plate 1 of Example 1 of the present embodiment is manufactured. In the first embodiment, the divergence position in the Y direction of the light source of the object light Om is set to the divergence position Fm1 on the opposite side to the observer of the CGH original plate 1. Therefore, as shown in FIG. 7, the object light Om is emitted from the point light sources P1... Pm... PM in the X direction and is emitted without spreading in the Y direction, and the divergence positions F11. It is set to spread from FM1. For this reason, although some astigmatism occurs, since the distance between the original image O and the CGH original 1 is very short, there is almost no influence.

  When the light source is set in this manner, the reference light L is irradiated at a predetermined incident angle, and the object light Om and the reference light L are set to interfere with each other, interference fringes are formed in the unit area Bm of the CGH original plate 1 shown in FIG. Interference fringes with intervals Cm1, Cm2, Cm3,..., Cmt,. In the first embodiment, the interference fringe interval appears so as to spread from top to bottom with respect to the paper surface. That is, the CGH original plate 1 is manufactured so that the spatial frequency on the side of the interference fringe interval Cm1 is high and the spatial frequency on the side of the interference fringe interval CmT is low.

  FIG. 8 is a diagram showing a case where the reproduction illumination light 2 made of monochromatic light is irradiated to the CGH original plate 1 produced as in the first embodiment shown in FIGS. 6 and 7. When the reproduction illumination light 2 of monochromatic light is irradiated on the CGH original plate 1 shown in FIGS. 6 and 7, the diffracted light 3 diffracted by the CGH original plate 1 is circular when viewed from the side as shown in FIG. It spreads in an arc and proceeds while expanding the viewing zone in the Y direction.

  FIG. 9 is a diagram illustrating a state when the CGH original plate 1 of Example 2 of the present embodiment is manufactured. In the second embodiment, the focusing position in the Y direction of the object light Om is set to the focusing position Fm2 on the observer side with respect to the CGH original. Therefore, the object light Om is emitted from the point light sources P1... Pm... PM without spreading in the Y direction in the X direction perpendicular to the paper surface, and is emitted from the converging positions F12... Fm2. Is set. For this reason, although some astigmatism occurs, since the distance between the original image O and the CGH original 1 is very short, there is almost no influence.

  When the light source is set in this manner, the reference light L is irradiated at a predetermined incident angle, and the object light Om and the reference light L are set to interfere with each other, interference fringes are formed in the unit area Bm of the CGH original plate 1 shown in FIG. Interference fringes with intervals Cm1, Cm2, Cm3,..., Cmt,. In the second embodiment, the interference fringe interval appears so as to narrow from the top to the bottom with respect to the paper surface. That is, the CGH original plate 1 is manufactured so that the spatial frequency on the side of the interference fringe interval Cm1 is low and the spatial frequency on the side of the interference fringe interval CmT is high.

  10 to 13 are diagrams showing other examples of the diverging position Fm1 or the focusing position Fm2 of the object light in the Y direction. FIG. 10 is a diagram showing a case where the divergence position Fm1 is arranged near the CGH original plate 1. FIG. In this case, the spread of the viewing area in the Y direction is increased. FIG. 11 is a diagram showing a case where the divergence position Fm1 is arranged far away from the CGH original plate 1. FIG. In this case, the spread of the viewing area in the Y direction is reduced. FIG. 12 is a diagram showing a case where the positional relationship between the CGH original plate 1 and the diverging position Fm1 is constant with respect to all the unit areas B1, B2, B3,..., Bm,. In this case, the design becomes easy and the calculation load is small. FIG. 13 is a diagram showing a case where the positional relationship between the CGH original plate 1 and the diverging position Fm1 is different for each of the unit areas B1, B2, B3,..., Bm,. In this case, the viewing area in the Y direction can be changed for each of the unit areas B1, B2, B3,..., Bm,. In the example shown in FIG. 13, the range in which the reproduction light toward the observer from the upper and lower unit areas can be seen simultaneously is wide.

  FIG. 14 is a diagram illustrating a case where the reference light L is focused at a predetermined focusing position G for each unit region, and the object light does not spread in the Y direction. As shown in FIG. 15, when the reference light L is focused at a predetermined focusing position G in the Y direction for each unit region Bm, and the object light Om is set as a linear light source that does not spread in the Y direction, the unit of the CGH original 1 The interference fringes in the region Bm appear such that the interference fringe spacings Cm1, Cm2, Cm3,..., Cmt,. That is, the CGH original plate 1 is manufactured so that the spatial frequency on the side of the interference fringe interval Cm1 is high and the spatial frequency on the side of the interference fringe interval CmT is low. Further, the focusing position G in the Y direction may be on the side opposite to the observer of the hologram, and in this case, the interval in the Y direction is produced so that the spatial frequency on the Cm1 side is high and the spatial frequency on the CmT side is low. .

  Next, a method for producing a volume hologram based on the present invention from the CGH original plate 1 obtained as described above will be described. First, an embodiment for producing an H1 hologram 11 from the obtained CGH original 1 will be described. FIG. 15 is a view showing a photographing arrangement when the first stage H1 hologram 11 is produced from the CGH original plate 1. FIG.

  First, in order to produce the first-stage H1 hologram 11 from the CGH original plate 1, as shown in FIG. 15, the photosensitive material for H1 hologram recording such as a photopolymer, a silver salt material, and the like is spaced apart facing the CGH original plate 1. 11 is arranged. Then, the CGH original plate 1 is irradiated with the first reproduction illumination light 2 at a predetermined incident angle from the opposite side of the CGH original plate 1 from the H1 hologram recording photosensitive material 11, and the first diffracted light 3 is generated from the CGH original plate 1. The first diffracted light 3 is made incident on the photosensitive material 11 for H1 hologram recording.

  Then, together with the first diffracted light 3, the first reference light 4 made of parallel light from the same light source coherent with the first diffracted light 3 at the incident angle θ is simultaneously incident on the surface of the photosensitive material 11 for H1 hologram recording, The hologram of the first reproduced image O ′ is exposed to the photosensitive material 11 for H1 hologram recording. At this time, it is preferable that the 0th-order light (light transmitted without being diffracted by the CGH original plate 1) of the first reproduction illumination light 2 is not covered with the H1 hologram recording photosensitive material 11 because noise is reduced. Then, the H1 hologram recording photosensitive material 11 on which the hologram is exposed is post-processed to produce the H1 hologram 11. Here, the H1 hologram recording photosensitive material 11 and the H1 hologram 11 are denoted by the same reference numeral 11.

  In this way, the parallax is only in the first direction X, and the diffraction pattern intervals Cm1, Cm2, Cm3,..., CmT in the Y direction in the unit regions B1, B2, B3,. Since a different computer-generated hologram 1 is produced and the volume-type H1 hologram 11 is produced using the computer-generated hologram 1 with an enlarged viewing area in the Y direction, a lenticular lens or a uniaxial diffusing plate is not used as in the prior art. The diffusion angle of the diffracted light can be changed, and a reflection-type or transmission-type volume hologram with an enlarged viewing area in the Y direction can be obtained.

  It is also possible to produce other different volume holograms from the obtained H1 hologram 11. FIG. 16 is a view showing a photographing arrangement when the second stage H2 hologram 21 is produced from the first stage H1 hologram 11, and FIG. 17 is a third stage H3 having the same characteristics from the H2 hologram 21 produced as a reflection type. It is a figure which shows the imaging | photography arrangement | positioning at the time of replicating the hologram.

  As shown in FIG. 16, an H2 hologram recording photosensitive material 21 such as a photopolymer or a silver salt material is arranged apart from the CGH original plate 1 side when recording the obtained H1 hologram 11, and the recording is performed at the first time. The second reproduction illumination light 5 traveling in the direction opposite to the first reference light 4 is incident on the H1 hologram 11 from the side opposite to the side on which the first reference light 4 is incident. At this time, it is preferable that the 0th-order light of the second reproduction illumination light 5 is not covered with the H2 hologram recording photosensitive material 21 because noise is reduced.

  Then, the second diffracted light 6 is generated from the H1 hologram 11, and the second diffracted light 6 and the parallel light from the same light source coherent with the second diffracted light 6 at a predetermined incident angle on the surface of the photosensitive material 21 for H2 hologram recording. The second reference light 7 made of light is simultaneously incident, and the hologram of the reproduced image O ′ is exposed on the H2 hologram recording photosensitive material 21. At this time, when the H2 hologram 21 is a transmission type, the second reference light 7 is incident from the same side as the second diffracted light 6, and when the H2 hologram 21 is a reflection type, the second reference light 7 is Incident from the side opposite to the diffracted light 6. The photosensitive material 21 for recording the H2 hologram on which the hologram is exposed is post-processed to produce the H2 hologram 21. Here, the H2 hologram recording photosensitive material 21 and the H2 hologram 21 are denoted by the same reference numeral 21.

  Next, an example in which another different volume hologram is produced from the obtained H2 hologram 21 will be described. FIG. 17 is a view showing a shooting arrangement when replicating an H3 hologram 31 having the same characteristics as that of the H2 hologram 21 manufactured as a reflection type. As shown in FIG. 17, a volume type H3 hologram photosensitive material 31 such as a photopolymer or the like is placed in close contact with an H2 hologram 21 made of a volume type reflection hologram or in close contact with a refractive index matching liquid. Then, the third reproduction illumination light 8 traveling from the H3 hologram photosensitive material 31 side to the H2 hologram 21 in the opposite direction to the second reference light 7 at the time of H2 hologram production shown in FIG. 16 is supplied to the second reference light 7 at the time of H2 hologram production. Is incident from the opposite side to the incident side. Then, the third reproduction illumination light 8 incident on the H3 hologram photosensitive material 31 and the third diffracted light 9 from the H2 hologram 21 (traveling opposite to the second diffracted light 6) are caused to interfere in the H3 hologram photosensitive material 31. The H2 hologram 21 is duplicated as the H3 hologram 31 on the H3 hologram photosensitive material 31.

  Conventionally, when the H1 hologram 11, the H2 hologram 21 or the H3 hologram 31 is produced from the CGH master 1, it is orthogonal to the one-dimensional direction compared to the lateral viewing area as a one-dimensional direction in which the point light source spreads during recording. Since the vertical viewing zone is narrow, each reproduction illumination light and diffracted light was diffused by a predetermined angle in the vertical direction perpendicular to the one-dimensional direction using a diffusing element such as a lenticular lens or a uniaxial diffusing plate. .

  In this way, the parallax is only in the first direction X, and the diffraction pattern intervals Cm1, Cm2, Cm3,..., CmT in the Y direction in the unit regions B1, B2, B3,. A different computer-generated hologram 1 is produced, and a volume-type H1 hologram 11 is produced by using the computer-generated hologram 1 in which the viewing area in the Y direction is enlarged. From the H1 hologram 11, the volume-type H2 hologram 21 and the volume-type H3 are produced. The holograms 31 can be produced one after another, and the reflection angle or the transmission type in which the diffusion angle of the diffracted light can be changed and the viewing area in the Y direction is enlarged without using a lenticular lens or a uniaxial diffusing plate as in the prior art. The volume hologram can be easily produced.

  As mentioned above, although the volume hologram produced by the method of the present invention and the volume hologram produced by the method have been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications are possible.

It is a perspective view which shows the concept of the recording method of the computer composition hologram which concerns on this invention. It is a figure which shows the specific example based on the concept of the arithmetic processing of FIG. It is a top view for demonstrating the concept of the arithmetic processing of FIG. It is a figure which shows the structure of the CGH original plate of this embodiment. It is a figure which shows the specific structure of the CGH original plate of this embodiment. It is a figure which shows the state at the time of CGH original plate preparation of Example 1 of this embodiment. It is a perspective view which shows the state at the time of CGH original plate preparation of Example 1 of this embodiment. It is a figure which shows the case where the reproduction illumination light which consists of monochromatic light is irradiated to the CGH original plate of Example 1. FIG. It is a figure which shows the state at the time of CGH original plate preparation of Example 2 of this embodiment. It is a figure which shows the other example of the divergence position Fm1 of a Y direction. It is a figure which shows the other example of the divergence position Fm1 of a Y direction. It is a figure which shows the other example of the divergence position Fm1 of a Y direction. It is a figure which shows the other example of the divergence position Fm1 of a Y direction. It is a figure which shows the case where the reference light L is made into the light which converges to the predetermined condensing position G, and object light is made into the light which does not spread in a Y direction. It is a figure for demonstrating embodiment of the method of producing the 1st volume hologram from the CGH original plate 1. FIG. It is a figure for demonstrating embodiment of the method of producing a 2nd volume type hologram from a 1st volume type hologram. It is a figure which shows the imaging | photography arrangement | positioning at the time of replicating a reflective 3rd volume hologram from a 2nd volume hologram.

Explanation of symbols

1 ... CGH master (recording medium for CGH master)
2 ... Reproduction illumination light, first reproduction illumination light 3 ... Diffraction light, first diffracted light 4 ... First reference light 5 ... Second reproduction illumination light 6 ... Second diffracted light 7 ... Second reference light 8 ... Third reproduction Illumination light 9 ... third diffracted light 11 ... H1 hologram recording photosensitive material (H1 hologram)
21 ... H2 hologram recording photosensitive material (H2 hologram)
31 ... Photosensitive material for H3 hologram recording (H3 hologram)

Claims (8)

In a method for producing a volume hologram using a computer-generated hologram formed by recording amplitude information and phase information on a predetermined recording surface by calculation using a computer,
The computer-generated hologram is
A first direction and a second direction orthogonal to the first direction;
Having parallax only in the first direction;
Each unit region having a predetermined width in the second direction,
Within each unit region, diffraction patterns having different spatial frequencies in the second direction are produced,
The computer-generated hologram is irradiated with first reproduction illumination light to generate first diffracted light from the computer-generated hologram to reproduce a first reproduced image, and the first diffracted light is applied to the first-stage hologram recording material. A method for producing a volume hologram, wherein the first reference beam is simultaneously incident to record a first-stage hologram of a reflection type or a transmission type.   Two stages arranged near the second reproduction image by irradiating the first stage hologram with second reproduction illumination light to generate second diffracted light from the first stage hologram to reproduce the second reproduction image. 2. The second-stage hologram is recorded as a reflection-type or transmission-type volume hologram by simultaneously causing the second diffracted light and the second reference light to enter the hologram recording material of the eye. A method for producing a volume hologram.   3. The volume hologram manufacturing method according to claim 1, wherein the spatial frequency of the diffraction pattern gradually changes from one to the other in the unit region. 4. Spreading from the point light source set on the recording object in the first direction,
The method for producing a volume hologram according to any one of claims 1 to 3, wherein recording is performed using object light that spreads in the second direction from a position different from the point light source. Extends from the linear light source set on the recording object in the first direction,
The object light having a certain width in the second direction is used, and the reference light is recorded using the reference light that is focused on a predetermined position determined for each unit region in the second direction. The method for producing a volume hologram according to any one of claims 1 to 3.   6. The method for producing a volume hologram according to claim 1, wherein the diffraction pattern includes interference fringes.   The method for producing a volume hologram according to claim 1, wherein the diffraction pattern is a pattern that modulates a phase and an amplitude.   A volume hologram produced by the volume hologram production method according to claim 1.

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