JP2778362B2 - Hologram fabrication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a three-dimensional image hologram for reconstructing parallax images in a plurality of directions different from each other, and more particularly to a method for producing a stable three-dimensional image in which individual pixels are uniform in a very short time. The present invention relates to a method for producing a hologram capable of obtaining a hologram having a simple image.

[0002]

2. Description of the Related Art Conventionally, for example, a 3D printer is one of the techniques for producing a hologram of a three-dimensional image. This 3D printer automatically creates a hologram of a three-dimensional image using a computer.

That is, a computer calculates an original image pattern for exposing each point of a hologram from original three-dimensional data, and displays this on a spatial modulation element (for example, a liquid crystal panel).

Further, a laser beam is modulated by an original image pattern and focused on a photosensitive material surface mounted on an XY stage to expose one element hologram. At this time, a dot composed of a desired diffraction grating is formed at that position.

A hologram for reproducing a parallax image is prepared by arranging dots in accordance with the image data by exposing the photosensitive material so as to fill the entire surface of the photosensitive material while sequentially moving the photosensitive material in accordance with the image data on the XY stage. Things.

By the way, in such a method of producing a three-dimensional hologram using a 3D printer, a hologram having parallax in the vertical and horizontal directions can be produced, but there are the following problems.

That is, it takes time to calculate the original image pattern, and furthermore, it takes time to produce a hologram because dots are exposed one by one.

Further, since the laser beam is used while being spread, not only is it difficult to produce a bright hologram, but also there is a problem that it is weak against vibration.

[0009]

As described above, the conventional hologram manufacturing method has a problem that not only a long time is required for manufacturing the hologram but also a stable hologram cannot be manufactured.

The present invention has been made to solve the above problems, and an object of the present invention is to produce a stable three-dimensional image hologram in which individual pixels are uniform in an extremely short time. It is an object of the present invention to provide a method for producing a hologram with high reliability.

[0011]

In order to achieve the above object, in a method for producing a hologram of a three-dimensional image, first, according to the first aspect of the present invention, a photosensitive material surface is
A first master hologram created so that the direction of the diffracted light is limited to the first direction is superimposed, and a spatial light modulator is arranged on the first master hologram.
The intensity of transmitted light at the corresponding position is controlled by the spatial light modulation element according to the first image data, a laser beam is made incident from the surface of the spatial light modulation element, and then the first master beam is applied to the photosensitive material surface. Instead of the hologram, a second master hologram created so that the direction of the diffracted light is limited to a second direction different from the first direction is superimposed, and the spatial light modulation element according to the second image data The intensity of the transmitted light at the corresponding position is controlled, and a laser beam is made incident from the surface of the spatial light modulator to produce a transmission hologram.

Further, in the invention according to claim 6, a first master hologram formed so that the direction of the diffracted light is limited to the first direction is superimposed on the surface of the photosensitive material,
A spatial light modulator is arranged on the surface of the photosensitive material opposite to the first master hologram, and the spatial light modulator controls the intensity of transmitted light at the corresponding position according to the first image data, and Laser light is incident from the surface of the light modulation element, and then, on the photosensitive material surface, the direction of the diffracted light is limited to a second direction different from the first direction instead of the first master hologram. The second master hologram created in the above is superimposed, the intensity of transmitted light at the corresponding position is controlled by the spatial light modulator according to the second image data, and laser light is incident from the surface of the spatial light modulator. ,
A reflective hologram is produced.

[0013] Here, particularly, as the above-mentioned laser light, a laser light expanded to a size sufficiently covering the exposure area is used.

Further, the laser beam is a laser beam spread linearly, and the exposure is performed by scanning in one direction.

Further, a laser beam is used as the laser beam, and exposure is performed by scanning in two directions.

Further, as the first and second master holograms, three R, G, and B holograms are used, respectively.

[0017]

Therefore, in the method of manufacturing a hologram according to the first aspect of the present invention, a master hologram formed so that the direction of diffracted light is limited on the surface of the photosensitive material, and the master hologram is further formed. By arranging a spatial light modulator on top, controlling the intensity of transmitted light at the corresponding position according to image data by the spatial light modulator, and causing laser light to enter from the surface of the spatial light modulator,
A transmission-type hologram that can be observed only from a limited direction of the image is produced, and the above-described production process is repeatedly performed by replacing the master hologram superimposed on the surface of the photosensitive material with image data, thereby providing a stereoscopic image by binocular parallax. A transmission hologram capable of observing an image can be manufactured.

In the method of manufacturing a hologram according to the present invention, a master hologram formed so as to restrict the direction of diffracted light is superimposed on the surface of the photosensitive material. A spatial light modulator is arranged on the surface opposite to the master hologram, the intensity of transmitted light at the corresponding position is controlled by the spatial light modulator according to image data, and laser light enters from the surface of the spatial light modulator. By producing a reflection-type hologram in which an image can be observed only from a limited direction, the above-mentioned production process is repeated by replacing the master hologram superimposed on the surface of the photosensitive material with image data and thereby performing both processes. A reflection hologram capable of observing a stereoscopic image by eye parallax can be manufactured.

As described above, a transmission type or reflection type hologram of a stable three-dimensional image in which individual pixels are uniform can be manufactured in a very short time.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. Here, a case where a transmission type hologram is manufactured as the hologram will be described.

In this embodiment, a transmission type hologram is manufactured by the following steps.

First, as shown in FIGS. 1 (a) and 1 (c), a dry plate 1 having a substrate coated with a photosensitive material is irradiated with object light 2 and reference light 3 from the directions shown in FIG. Is limited to the first direction (left direction in the figure), so that the transmission-type first master hologram 4
Create

Next, as shown in FIGS. 1B and 1C, another dry plate 5 on which a photosensitive material is applied to a substrate is irradiated with object light 6 and reference light 7 from the illustrated directions, respectively. Then, the transmission-type second master hologram 8 is created so that the direction of the diffracted light is limited to a second direction (right direction in the figure) different from the first direction.

Next, as shown in FIG. 2, a dry plate 11 coated with a photosensitive material on a substrate is placed with the photosensitive material surface facing up, and the first material prepared above is placed on the photosensitive material surface of the dry plate 11.
The master hologram 4 is placed and superimposed, and a spatial light modulator (liquid crystal element, film, etc.) 12 is arranged on the first master hologram 4.

Next, the first image data is read by a computer (not shown), and the spatial light modulation element 12 selects transmission / blocking of light at the corresponding position according to the first image data. 14 to mirror 15
Then, the laser light is reflected by the lens 16 and further expanded to a size sufficient to cover the exposure area by the lens 16 and is incident from the surface of the spatial light modulation element 12 and exposed, thereby completing the recording of the image for the left eye.

Next, the first master hologram 4 on the dry plate 11 is removed, and the second master hologram 8 prepared above is placed on the photosensitive material surface of the dry plate 11 instead.
And place them on top of each other.

Next, the second image data is read by a computer (not shown), and the spatial light modulator 12 selects the transmission / interruption of the light at the corresponding position according to the second image data. 14 to mirror 15
Then, the laser light is reflected by the lens 16 and further expanded by a size sufficient to cover the exposure area by the lens 16 and is incident from the surface of the spatial light modulation element 12 and exposed, thereby completing the recording of the image for the right eye.

By completing the recording of the left and right images as described above, a transmission type three-dimensional image hologram (3D display) is produced.

FIG. 3 is an enlarged view showing a state when the laser light 14 is incident on the spatial light modulator 12.

In FIG. 3, the light (0) transmitted through the light transmitting portion of the spatial light modulator 12 and the first master hologram 4 is shown.
Second order diffracted light) 17 is applied to the photosensitive material 11A (11B
Is a reference light, and the first-order diffracted light 18 of the first master hologram 4 becomes object light and interferes, and the interference fringes are recorded on the photosensitive material 11A of the dry plate 11.

At this time, if the distance between the first master hologram 4 and the photosensitive material 11A of the dry plate 11 is small, the exposed portion is a dot substantially in the shape of the light transmitting portion of the spatial light modulator 12 become. By expressing an image using these dots as pixels, the direction in which the image is reproduced (the direction of the left eye) is determined by the first master hologram 4 placed at that time.

Also, for the second master hologram 8, the direction in which the image is reproduced (the direction of the right eye) is determined in the same manner as described above.

Therefore, when observing the transmission type hologram produced as described above, as shown in FIG.
The diffracted light 4A from the dot created by using the master hologram 4 enters the left eye of the observer 19 and
The diffracted light 8A from the dot created by using the master hologram 8 enters the right eye of the observer 19, so that different images can be observed from different directions, and a three-dimensional image can be recognized. Can be.

As described above, in the present embodiment, when producing a transmission type three-dimensional image hologram, first, the direction of the diffracted light is placed on the photosensitive material surface of the dry plate 11 on which the photosensitive material 11A is coated on the substrate 11B. Are overlapped with the first master hologram 4 created so that is limited to the left direction,
A spatial light modulator 12 is arranged on the first master hologram 4, and the spatial light modulator 12 selects transmission / blocking of light at the corresponding position in accordance with the first image data. Light 14 to mirror 15
The laser beam is reflected from the surface of the spatial light modulation element 12 as a laser beam expanded to a size sufficiently covering the exposure area by the lens 16, and then the first master hologram is placed on the photosensitive material surface of the dry plate 11. 4, a second master hologram 8 created so that the direction of the diffracted light is limited to the right direction is superimposed, and the spatial light modulator 12 modulates the light at the corresponding position according to the second image data. Select transmission / blocking, and apply laser light 14 from laser light source 13 to mirror 1
The laser beam is reflected by the lens 5 and is made to spread from the surface of the spatial light modulator 12 as laser light expanded to a size sufficiently covering the exposure area by the lens 16 to produce a transmission hologram.

Accordingly, the following various effects can be obtained.

(A) Since the copy method is employed, the hologram of the present invention is resistant to vibration and uses light effectively, so that the exposure time is short, and as a result, a hologram of a bright and stable image is produced in a very short time. It is possible to do.

(B) Since separate images can be recorded in the left and right directions, it is possible to produce a hologram that can be viewed stereoscopically.

(C) For the above reasons, it is possible to automate the production of the hologram.

(D) Since an image can be directly output, an intermediate operation such as outputting to a film as in the conventional art is not required.

(E) Since the hologram can be manufactured using only the laser light source 13, the mirror 15, the lens 16, the master holograms 4, 8, and the dry plate 11, the configuration of the apparatus can be simplified.

(F) Since the laser light 14 is made incident on the master holograms 4 and 8 via the spatial light modulator (liquid crystal element, film, etc.) 12, the shape of the dots is not limited, and individual images It becomes possible to make it suitable for the shape.

(G) Since the laser beam 14 is a laser beam which is wide enough to cover the exposure region, the laser beam 14 is exposed to light in an intensity distribution (normally Gaussian distribution) in a plane perpendicular to the optical axis of the laser beam. It is possible to eliminate unevenness and make the brightness uniform within the dot.

(H) When a laser beam is used, the diameter of the hologram pixel, ie, the resolution, is limited to about 80 μm. However, when a liquid crystal element is used as the spatial light modulator 12, for example, the diameter is about 30 μm. And high resolution can be achieved.

(I) When a gradation is expressed using a laser beam, the size and brightness of the exposed dot are changed by changing the exposure time, but the size of the dot is not constant. Although it is difficult to see the image, as in the present embodiment, for example, by using a liquid crystal element, by giving gradation in each cell of the liquid crystal element, dots of uniform size and different brightness can be easily created. It becomes possible.

Next, another embodiment of the present invention will be described. Here, a case in which a reflection hologram is manufactured as the hologram will be described.

In this embodiment, a reflection type hologram is manufactured by the following steps.

First, as shown in FIGS. 5A and 5C, the object light 2 is placed on a dry plate 21 having a substrate coated with a photosensitive material.
2 and the reference light 23 are respectively radiated from the illustrated direction so that the direction of the diffracted light is the first direction (left direction in the figure).
The first master hologram 24 of the reflection type is created so as to be limited to the following.

Next, as shown in FIGS. 5 (b) and 5 (c), the object light 26 and the reference light 27 are irradiated from the illustrated direction onto another dry plate 25 having a photosensitive material applied to the substrate. A second direction in which the direction of the diffracted light is different from the first direction.
The second master hologram 28 of the reflection type is created so as to be limited to the direction (right direction in the figure).

Next, as shown in FIG. 6, a dry plate 31 coated with a photosensitive material on a substrate is placed on the first master hologram 24 prepared as described above with the photosensitive material face down, and superposed. Further, a spatial light modulator 32 is arranged on the surface of the photosensitive material opposite to the first master hologram 24.

Next, the first image data is read by a computer (not shown), and the spatial light modulator 32 selects the transmission / interruption of the light at the corresponding position in accordance with the first image data. 34 to mirror 35
Then, the laser light is reflected by the lens 36, and the laser light is expanded to have a size enough to cover the exposure area by the lens 36. The laser light is incident from the surface of the spatial light modulator 32 and exposed, thereby completing the recording of the image for the left eye.

Next, the first master disk on the lower surface of the dry plate 31
The hologram 24 is removed, and instead, the second master hologram 28 created above is placed on the lower surface of the dry plate 31.
And place them on top of each other.

Next, the second image data is read by a computer (not shown), and the spatial light modulation element 32 selects the transmission / interruption of the light at the corresponding position according to the second image data. 34 to mirror 35
The laser light is then reflected by the lens 36, and the laser light is expanded so as to sufficiently cover the exposure area by the lens 36. The laser light is incident from the surface of the spatial light modulation element 32 and exposed, thereby completing the recording of the image for the right eye.

By completing the recording of the left and right images as described above, a hologram (3D display) of a transmission type three-dimensional image is produced.

FIG. 7 is an enlarged view showing a state where the laser light 34 is incident on the spatial light modulator 32.

In FIG. 7, the light 37 transmitted through the light transmitting portion of the spatial light modulator 32 and the dry plate 31 serves as reference light for the photosensitive material 31A (31B is a substrate) of the dry plate 31, and becomes the first master light. First order diffracted light 3 reflected by hologram 24
8 interferes as object light, and the interference fringes are recorded on the photosensitive material 31A of the dry plate 31.

At this time, if the distance between the first master hologram 24 and the photosensitive material 31A of the dry plate 31 is small, the exposed portion is a dot substantially in the shape of the light transmitting portion of the spatial light modulator 32. become. By expressing an image using these dots as pixels, the direction in which the image is reproduced (the direction of the left eye) is determined by the first master hologram 24 arranged at that time.

Also, for the second master hologram 28, the direction in which the image is reproduced (right-eye direction) is determined in the same manner as described above.

Therefore, when observing the reflection type hologram produced as described above, the diffracted light from the dot produced by using the first master hologram 24 enters the left eye of the observer, and Master hologram 2
When the diffracted light from the dots created by using No. 8 enters the right eye of the observer, different images can be observed from different directions, and a reflection type three-dimensional image can be recognized.

In the method of producing a hologram of a reflection type image according to the present embodiment, exactly the same effects as in the above embodiment can be obtained.

The present invention is not limited to the above embodiments, but can be implemented in the following manner.

(A) In each of the above-described embodiments, the case where the laser light 14 from the laser light source is expanded to a size sufficiently covering the exposure area is used as the laser light. As shown in FIG.
1 is placed on an XY stage 41, the transmittance of the spatial light modulator 12 at a corresponding position is controlled in accordance with image data, and the XY stage 41 is moved, or the laser beam 42 is moved in two directions. The same effect as described above can be obtained by exposing the entire area with image data by directly inputting the laser beam 42 from the laser light source 13 through the mirror 43 while scanning It is. The same applies to the case of a reflection type hologram.

(B) In each of the embodiments described above, a case is used in which laser light from a laser light source is expanded to a size sufficient to cover the exposure area as the laser light. As shown in (2), the dry plate 11 is placed on the X stage 44, and the laser beam 45 from the laser light source 13 is linearly spread through the mirror 46 and the cylindrical lens 47 to be incident.
Even if the exposure is performed by scanning in one direction, the same effect as described above can be obtained. The same applies to the case of a reflection type hologram.

(C) In each of the above embodiments, the description has been given of the case of two parallax images on the left and right sides. However, the present invention is not limited to this case.
By preparing a hologram, it is possible to obtain a hologram of a three-dimensional three-dimensional image that is more easily viewable in the same manufacturing process as described above.

(D) In each of the above embodiments, the first and second
3 master holograms for R, G, B (1
By using (for each direction), it is also possible to realize colorization.

(E) In each of the above embodiments, the master
The method for creating a hologram is not limited to the methods shown in FIGS. 1 and 5 described above. For example, a master hologram may be created as follows.

First, as shown in FIGS. 10A and 10C, a reference light 52 and an object light 54 obtained through a diffusion plate 53 are applied to a dry plate 51 having a substrate coated with a photosensitive material.
Are respectively irradiated from the directions shown in the figure to create a first master hologram diffusion hologram such that the direction of the diffracted light is limited to the first direction (left direction in the figure).

Next, as shown in FIGS. 10B and 10C, the reference light 56 and the object light 5 obtained via the diffusion plate 57 are placed on another dry plate 55 on which a photosensitive material is applied to a substrate.
The second diffusion hologram for the master hologram is created by irradiating 8 from the illustrated directions so that the direction of the diffracted light is limited to the second direction (right direction in the figure).

Next, as shown in FIGS. 11A and 11C, a dry plate 61 having a substrate coated with a photosensitive material is provided with a reference light 62 and a reproduction light which is a conjugate light of the reference light 52 at the time of photographing. By irradiating the object light 65 obtained through the first master hologram diffusion hologram 64 with the illumination light 63 from the directions shown in the drawing, the direction of the diffracted light becomes the first.
The first master hologram 66 is created so as to be limited to the direction (left direction in the figure).

Similarly, as shown in FIGS. 11B and 11C, a dry plate 7 having a substrate coated with a photosensitive material is used.
1. The reference light 72 and the reproduction illumination light 73 are
By irradiating the object light 55 obtained through the master hologram diffusion hologram 74 from the illustrated direction, the diffracted light is limited to the second direction (right direction in the figure) so that the A second master hologram 76 is created.

Thereafter, the first and second data created in this manner are
Using the master holograms 66 and 76 described above, a transmission-type or reflection-type hologram is manufactured in the same manner as in the above-described embodiments.

When observing the transmission type or reflection type hologram manufactured as described above, even if the observation position is shifted from the center, a three-dimensional image can be surely seen over a relatively wide range. is there.

(F) In each of the above embodiments, the case has been described in which the transmission / blocking of the light at the corresponding position is selected by the spatial light modulation element according to the first / second image data. The intensity of transmitted light at the corresponding position may be controlled by the modulation element according to the first / second image data.

(G) In each of the above-described embodiments, two methods have been described as methods for producing a master hologram. However, the present invention is not limited to this, as long as the output direction of the diffracted light is limited. Good.

[0074]

As described above, according to the present invention, a master hologram formed so as to restrict the direction of diffracted light is superimposed on a photosensitive material surface, and a spatial light is superimposed on the master hologram. A modulation element is arranged, the intensity of transmitted light at the corresponding position is controlled according to image data by the spatial light modulation element, and laser light is incident from the surface of the spatial light modulation element, or diffracted light The master hologram created so that the direction is limited is superimposed, and further a spatial light modulator is arranged on the surface of the photosensitive material surface opposite to the master hologram, and the spatial light modulator according to the image data. A master hologram that controls the intensity of transmitted light at the corresponding position, injects laser light from the surface of the spatial light modulator, and superimposes it on the photosensitive material surface Since such repeated to place the image data can be provided a very short time and stable multi-tone steric high hologram manufacturing method of a reliable capable of producing a hologram image.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a case where a transmission-type master hologram according to the present invention is created.

FIG. 2 is a schematic configuration diagram showing one embodiment in the case of producing a transmission type hologram according to the present invention.

FIG. 3 is an enlarged view showing a state when laser light is incident on the spatial light modulator in the embodiment.

FIG. 4 is a schematic diagram for explaining a method of observing a hologram produced by the method of the embodiment.

FIG. 5 is a schematic diagram showing an example of a case where a reflection type master hologram according to the present invention is created.

FIG. 6 is a schematic configuration diagram showing one embodiment in the case of producing a reflection type hologram according to the present invention.

FIG. 7 is an enlarged view showing a state when laser light is incident on the spatial light modulator in the embodiment.

FIG. 8 is a schematic diagram showing another example when a transmission-type master hologram according to the present invention is created.

FIG. 9 is a schematic diagram showing another example in the case of creating a transmission-type master hologram according to the present invention.

FIG. 10 is a schematic diagram showing another example when a master hologram according to the present invention is created.

FIG. 11 is a schematic diagram showing another example when a master hologram according to the present invention is created.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Dry plate, 2 ... Object light, 3 ... Reference light, 4 ... First master hologram, 5 ... Dry plate, 6 ... Object light, 7 ... Reference light,
8 ... second master hologram, 11 ... dry plate, 12 ...
Spatial light modulation element, 13 laser light source, 14 laser light, 15 mirror, 16 lens, 17 diffracted 0th order light,
18: first-order diffracted light, 19: observer, 21: dry plate, 22 ...
Object light, 23 ... Reference light, 24 ... First master hologram, 25 ... Dry plate, 26 ... Object light, 27 ... Reference light, 28
... second master hologram, 31 ... dry plate, 32 ... spatial light modulator, 33 ... laser light source, 34 ... laser light, 35 ... mirror, 36 ... lens, 37 ... transmitted light, 38
.. Primary diffraction light, 41 XY stage, 42 laser beam, 43 mirror, 44 X stage, 45 laser beam, 46 mirror, 47 cylindrical lens, 51 dry plate, 52 reference light , 53 ... Diffusion plate, 5
4 ... Object light, 55 ... Dry plate, 56 ... Reference light, 57 ... Diffusion plate, 58 ... Object light, 61 ... Dry plate, 62 ... Reference light, 63 ...
Illumination light for reproduction, 64: Diffusion hologram for first master hologram, 65: Object light, 66: First master hologram
Hologram, 71: dry plate, 72: reference light, 73: illumination light for reproduction, 74: diffusion hologram for second master hologram, 75: object light, 76: second master hologram.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-144881 (JP, A) JP-A-58-115469 (JP, A) JP-A-58-144880 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G03H 1/20 G03H 1/26

Claims (10)

(57) [Claims] 1. A method for producing a hologram for displaying a three-dimensional image, comprising: superimposing a first master hologram, which is produced so that the direction of diffracted light is limited to a first direction, on a surface of a photosensitive material. Arranging a spatial light modulator on the first master hologram, and controlling the intensity of transmitted light at the corresponding position according to the first image data by the spatial light modulator; Then, the direction of the diffracted light is limited to a second direction different from the first direction, instead of the first master hologram, on the photosensitive material surface. Superimposing the second master hologram created in step (a), controlling the intensity of transmitted light at the corresponding position by the spatial light modulator according to the second image data, and setting the laser from the surface of the spatial light modulator. A method for producing a hologram, characterized in that a hologram of a transmission type is produced by irradiating light. 2. The method of manufacturing a hologram according to claim 1, wherein the laser beam is a laser beam which is widened to a size enough to cover an exposure area. 3. The hologram manufacturing method according to claim 1, wherein the laser light is linearly spread laser light, and is exposed by scanning in one direction. 4. The method of manufacturing a hologram according to claim 1, wherein the laser beam is used as the laser beam, and the exposure is performed by scanning in two directions. 5. The method of manufacturing a hologram according to claim 1, wherein R, G, and B three holograms are used as the first and second master holograms, respectively. 6. A method for producing a hologram for displaying a three-dimensional image, wherein a first master hologram created so that the direction of diffracted light is limited to a first direction is superimposed on a photosensitive material surface. A spatial light modulator is disposed on the surface of the photosensitive material opposite to the first master hologram, and the intensity of transmitted light at the corresponding position is adjusted by the spatial light modulator according to the first image data. Controlling the laser light from the surface of the spatial light modulator, and then, in place of the first master hologram, the direction of the diffracted light is different from the first direction on the photosensitive material surface. Superimposing a second master hologram created so as to be limited to two directions, controlling the intensity of transmitted light at the corresponding position by the spatial light modulator according to second image data, A method for producing a hologram, wherein a reflection type hologram is produced by irradiating a laser beam from a surface of a light modulation element. 7. The method for producing a hologram according to claim 6, wherein the laser beam is a laser beam which is widened to a size enough to cover an exposure area. 8. The method of manufacturing a hologram according to claim 6, wherein the laser beam is a laser beam spread linearly, and the exposure is performed by scanning in one direction. 9. The method of manufacturing a hologram according to claim 6, wherein a laser beam is used as the laser beam, and exposure is performed by scanning in two directions. 10. The method of manufacturing a hologram according to claim 6, wherein three R, G, and B images are used as the first and second master holograms.