JP2007171250A - Hologram recording medium and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording medium in which a sealing portion of high reliability is easily and inexpensively provided on a recording layer in the outer rim of a hologram recording medium and to provide a method for manufacturing the medium. <P>SOLUTION: The method for manufacturing a hologram recording medium includes a step of forming a sealing portion by forming a recording layer 2 comprising a photosetting organic material that contains monomers, a hardening initiator and a sensitized dye on a transparent substrate 1, exposing the recording layer corresponding to the outer rim of the hologram recording medium to light L<SB>E</SB>at a photosensitive wavelength to harden the photosetting organic material so as to seal the photosetting organic material in a region inside the outer rim. The step of forming the sealing portion is carried out by exposing the recording layer while measuring the transmittance for the exposure light L<SB>E</SB>in the recording layer and then terminating the exposure when the transmittance measured reaches the transmittance or more corresponding to the end point of the hardening reaction of the photosetting organic material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hologram recording medium and a manufacturing method thereof.

  In recent years, hologram recording media have attracted attention as a next-generation large-capacity storage technology, and are applied in the fields of stereoscopic image display and security of credit cards and ID cards. Such a hologram recording medium is desired to be thin and have a high degree of freedom in changing the shape, and a substrate using a thin glass substrate or a resin film such as polycarbonate is considered.

  As a method of actually creating a hologram recording medium, a structure in which a recording layer is created and sandwiched on the entire surface of a simple flat substrate without giving a concave-convex structure to the substrate is considered in order to simplify the production. At that time, the recording layer is formed up to the medium edge portion.

  However, the recording layer edge portion of the medium having such a configuration is in contact with the outside air, and the recording layer medium leaks from the edge portion in an unrecorded state. In addition, since it is in direct contact with the outside air, deterioration such as corrosion has occurred, and a phenomenon has occurred in which the recording characteristics in the vicinity of the edge deteriorate.

  In order to prevent the deterioration of the characteristics at the edge portion of the hologram recording medium, it is conceivable to inject a recording material into the substrate surrounded by the peripheral portion. However, the processing of the substrate is complicated, and the production is not easy. Further, it is conceivable to sandwich a recording material on a flat substrate and locally heat the edge portion, or to heat-seal by applying ultrasonic waves or the like (see, for example, Patent Document 1). However, when heat treatment is performed in this way, a phenomenon occurs in which the recording layer reacts with heat and the recording characteristics deteriorate. Furthermore, there is a problem in that the edge is not uniformly sealed due to a difference in melting state between the substrate at the edge portion and the protective layer provided on the surface of the substrate.

  It is also conceivable that the recording layer is exposed to UV light of a short wavelength or blue laser light to cause a curing reaction to seal the edge (see, for example, Patent Document 2). There is a problem that the wavelength is limited and a high intensity light source cannot be freely selected.

JP-A-7-84504 JP 2004-29476 A

  The present invention has been made in view of the above problems in the prior art, and provides a hologram recording medium provided with a simple, low-cost and highly reliable seal portion on a recording layer at the outer edge of the hologram recording medium, and a method for manufacturing the same. The purpose is to provide.

  In order to solve the above-mentioned problems, the invention of claim 1 is that an outer edge of a hologram recording medium is formed after a recording layer made of a photocurable organic material containing a monomer, a curing initiator, and a sensitizing dye is formed on a transparent substrate. A sealing portion forming step of forming a region for sealing the photocurable organic material in the inner region from the outer edge portion by curing the photocurable organic material by exposing light of a photosensitive wavelength to the recording layer that hits the portion. A method of manufacturing a hologram recording medium, wherein in the seal portion forming step, the exposure is performed while measuring the transmittance of the light to be exposed in the recording layer, and the measured light transmittance is the photocurable organic The hologram recording medium manufacturing method is characterized in that the exposure is terminated when the transmittance becomes equal to or higher than the transmittance corresponding to the end point of the curing reaction of the material.

  According to a second aspect of the present invention, there is provided a hologram according to the first aspect of the invention, wherein the light used for exposure in the sealing portion forming step uses a light emitting diode as a light source. It is a manufacturing method of a recording medium.

  According to a third aspect of the present invention, there is provided a recording layer made of a photocurable organic material containing a monomer, a curing initiator that is sensitized at a predetermined wavelength, and a sensitizing dye on a transparent substrate. In the hologram recording medium, the recording layer includes a seal portion in which a photocurable organic material in a region corresponding to the outer edge portion of the hologram recording medium is cured and a recording region inside the outer edge portion, and the light having the photosensitive wavelength. The hologram recording medium is characterized in that the transmittance of the seal portion with respect to is equal to or higher than the transmittance corresponding to the end point of the curing reaction of the photocurable organic material.

  The invention of claim 4 provided to solve the above-mentioned problem is that an outer edge of a hologram recording medium is formed after a recording layer made of a photocurable organic material containing a monomer, a curing initiator, and a sensitizing dye is formed on a transparent substrate. A seal portion forming step of forming a region for curing the photocurable organic material by exposing light of a photosensitive wavelength to the recording layer that contacts the portion to seal the photocurable organic material in the inner region from the outer edge portion In the sealing portion forming step, the exposure is performed while measuring the transmittance of the light to be exposed in the recording layer, and the measured light transmittance corresponds to the end point of the curing reaction of the photocurable organic material. The hologram recording medium is manufactured by a method for manufacturing a hologram recording medium in which the exposure is terminated when the transmittance is exceeded.

  According to a fifth aspect of the present invention, there is provided a hologram recording medium according to the third or fourth aspect, wherein the transparent substrate is a glass substrate.

  According to a sixth aspect of the present invention, there is provided a hologram recording medium according to the third or fourth aspect, wherein the transparent substrate is a polycarbonate film.

  The invention of claim 7 provided to solve the above-mentioned problem is that, in the invention of claim 6, the birefringence amount of the transparent substrate is 30 as a phase difference (absolute value) with respect to light transmitted in the substrate thickness direction. The hologram recording medium is characterized in that it is less than or equal to the degree.

  The invention of claim 8 provided to solve the above-described problem is that, in the invention of claim 3 or 4, a protective layer for preventing deterioration of the recording layer is provided on the surface of the transparent substrate on the recording layer side. The hologram recording medium is characterized by the above.

  According to a ninth aspect of the present invention, there is provided protection for preventing damage to the transparent substrate on the surface of the transparent substrate opposite to the recording layer. A holographic recording medium comprising a layer.

  The invention of claim 10 provided to solve the above-mentioned problems is characterized in that, in the invention of claim 3 or 4, an antireflection film is provided on the surface of the transparent substrate opposite to the recording layer. It is a hologram recording medium.

According to the method for producing a hologram recording medium of the present invention, by adjusting the combination of a monomer, a curing initiator, and a sensitizing dye, the wavelength of light to be irradiated during the exposure process for the recording layer in the seal portion forming step However, the seal portion can be formed efficiently with inexpensive equipment. In addition, the curing reaction of the photocurable organic material proceeds according to the exposure amount at that time, but the transmittance of the seal portion changes with the progress of the curing reaction. The end point of the curing reaction of the photocurable organic material in the part can be detected, and the management of the seal part forming process becomes easy. In addition, since the transparent substrate is not subjected to response shape processing, a highly reliable hologram recording medium can be produced at low cost.
In addition, according to the hologram recording medium of the present invention, since the photocurable organic material of the seal portion is surely cured, material deterioration from the seal portion is reduced, and a highly reliable hologram recording medium is provided. be able to. Moreover, a film-like substrate such as polycarbonate can be used as the shape of the transparent substrate, and the size and shape can be easily changed, and a large-area hologram recording medium can be obtained.

Below, the manufacturing method of the hologram recording medium which concerns on this invention is demonstrated.
FIG. 1 is a schematic view showing a manufacturing process of a hologram recording medium according to the present invention.
(S11) First, a layer (photocurable organic material layer) 2a made of a photocurable organic material is provided between the two transparent substrates 1 (FIG. 1A). Specifically, a photo-curing organic material dissolved in a solvent is applied onto the transparent substrate 1 by a bar coater, spin coating, spraying, or the like, and the solvent is evaporated by heat treatment to form the layer 2a, and then the upper surface of the layer 2a Another transparent substrate 1 may be bonded together. Alternatively, a spacer is inserted between the two transparent substrates 1, and a layer of the photocurable organic material dissolved in a solvent is pressed into the gap to form a layer, and then the solvent is evaporated by heat treatment to remove the layer 2a. May be formed.

  Here, the transparent substrate 1 is preferably a thin substrate made of a material such as glass or polycarbonate resin. In particular, a polycarbonate resin is preferable because a film-like material having a large area exists and processing such as cutting of the substrate can be easily performed, so that the size and shape of the hologram recording medium can be relatively freely changed. Furthermore, it is preferable to use a polycarbonate resin which is a low birefringence material, since both the degree of freedom of the shape of the hologram recording medium and good recording characteristics can be achieved. The amount of birefringence of the substrate as described above is desirably 30 degrees or less in absolute value of phase difference with respect to light transmitted in the thickness direction of the substrate as a result of intensive studies. In addition, when a glass substrate is used, it is generally preferable because it has a low birefringence as compared with a resin, and good recording characteristics can be obtained.

  The photocurable organic material is a hologram material containing a monomer, a curing initiator, and a sensitizing dye, and constitutes the recording layer 2 of the hologram recording medium. In the recording layer 2, when used as a hologram recording medium, a hologram is recorded by a change in refractive index. That is, a photosensitive agent such as a curing initiator or a dye sensitive to a desired wavelength is blended in the material of the recording layer 2 so that the wavelength range of the light to be sensitized can be changed to a desired specific wavelength. When light in the wavelength region is irradiated, the photocuring reaction starts. At this time, the blended curing initiator, sensitizing dye, and the like change the transmittance at the wavelength according to the amount of light irradiated. Regarding the wavelength to be exposed, it is desirable to avoid a wavelength at which an action such as absorption occurs at the substrate, and to select a curing initiator, a sensitizing dye or the like, and it is preferably a visible light wavelength.

  The monomer contained in the photocurable organic material is preferably a radically polymerizable monomer or a cationically polymerizable monomer. For example, 2-phenoxyethyl acrylate, p-chlorophenyl acrylate, N-vinylcarbazole, N-phenylalemid, diglycerol Polyglycidyl ether, 3,4-epoxycyclohexylmethyl-3 ′, 4′-epoxycyclohexanecarboxylate, 2,2-bis (4-acryloxyethoxyphenyl) propane, acrylamide, methacrylamide, styrene, phenyl acrylate, etc. It is done.

  Examples of the curing initiator include hexaarylbisimidazole derivatives, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl)- Organic compounds used for radical polymerization such as butanone-1,1-hydroxy-cyclohexyl-phenyl-ketone, iodonium, (4-methylphenyl) [4- (2-methylpropyl) phenyl] -hexafluorophosphate (1-) And organic iodonium salts used for cationic polymerization.

Examples of the sensitizing dye include anhydro-3,3′-dicarboxylmethyl-9-ethyl-2,2′thiacarbocyanine betaine, 3,9-diethyl-3′-carboxymethyl-2,2′-thia. Examples include cyanine dyes such as carbocyanine / iodine salts, diphenyliodonium salts (DPI), squarylium dyes, and the like.
In addition, a binder polymer may be added.

(S12) Next, a sensitizing dye of a photocurable organic material from the light source G from the side of one transparent substrate 1 (upper side in the figure) in a region corresponding to the outer edge of the hologram recording medium in the photocurable organic material layer 2a. the photosensitive material is irradiated with visible light L _E wavelength reacting (photosensitive wavelength), the desired region of the photocurable organic material layer 2a performs processing for photosensitive. As a result, the exposed portion of the photocurable organic material layer 2a is cured to become a region (cured portion) 2b that seals the photocurable organic material inside the outer edge portion (FIG. 1B).

That is, when the one transparent substrate 1 (upward in the drawing) side performs irradiation of the visible light L _E, the visible light L _E is transmitted through the transparent substrate 1 to reach the photo-curable organic material layer 2a, the The sensitizing dye of the photocurable organic material is exposed to light, and the transmittance of the photocurable organic material layer 2a in this region changes according to the amount of light exposed. Here, the transmittance measuring device E is arranged on the other transparent substrate 1 (lower side in the figure), and the light transmitted through the transparent substrate 1, the photocurable organic material layer 2 a (cured portion 2 b), and the transparent substrate 1. so that by receiving (transmission light) L _T can measure the transmittance of light from the light source G. In this step, the exposure is performed while measuring the transmittance of light from the light source G, and the measured light transmittance is equal to or higher than the transmittance corresponding to the end point of the curing reaction of the photocurable organic material. This is the end of the exposure.

  The light source G is arbitrary as long as it is a light source in the wavelength range in which the photocurable organic material is exposed. However, it is preferable to use a high intensity light source to shorten the exposure time, and more preferably a mercury lamp, a xenon lamp, Examples include lasers and light emitting diodes (LEDs). In particular, when the wavelength width with which a photosensitive material such as a sensitizing dye reacts is narrow, it is desirable to use a light source with a narrow wavelength width such as a laser or LED. In addition, when an LED is used, a light source can be prepared at a low cost, and exposure processing can be performed by condensing to a desired beam width by a lens, a mirror, or the like. By using such a light source, it is possible to perform the photosensitive processing efficiently in a short time.

  In this step, condensed light may be used to improve the intensity of light applied to the photocurable organic material layer 2a (cured portion 2b). In order to prevent deterioration of the characteristics of the recording layer around the cured portion 2b due to scattering of the irradiated light, it is preferable to provide a light shielding mask or the like directly above the hologram recording medium.

(S13) Next, the edge part (the transparent substrate 1, the hardening part 2b, the transparent substrate 1) of a target object is cut | disconnected in the position containing the hardening part 2b (FIG.1 (c)). As a result, the outer shape of the hologram recording medium is adjusted to a predetermined size, and a part of the cured portion 2b remains as a seal portion on the outer edge portion of the hologram recording medium. At this time, if the width entering from the end of the object of the cured portion 2b (that is, the width of the photosensitive region of the photocurable organic material layer 2a) is set to 5 mm or more, the alignment of the cutting in this step can be easily performed. At the same time, it is possible to prevent deterioration of characteristics such as protrusion of the photocurable organic material from the end of the hologram recording medium and deterioration due to intrusion of water or air.

  Here, after the photocurable organic material layer 2a is formed between the two transparent substrates 1, the outer edge seal portion is formed. After the photocurable organic material layer 2a is formed on the outer peripheral portion, the outer edge seal portion is formed, and then another transparent substrate 1 is bonded onto the recording layer to produce a hologram recording medium. . In this case, the transparent substrate 1 may be bonded by putting the entire object under reduced pressure and performing a vacuum press. In any of these methods, a hologram recording medium having a large area can be produced by selecting various sizes of the transparent substrate 1.

  In addition, the processing procedures of steps S12 and S13 are interchanged, and the edge of the medium is cut before the photosensitive processing of the photocurable organic material layer 2a is performed, and then the photocurable organic material in the end region is photosensitively processed. Then, it may be cured.

Through the above steps, the hologram recording medium of the present invention is completed.
FIG. 2 shows a configuration example of the hologram recording medium.
As shown in FIG. 2A, the hologram recording medium 10 includes a seal portion 2d obtained by curing the photocurable organic material in a region corresponding to the outer edge portion of the hologram recording medium 10 on the transparent substrate 1, and the outer edge portion. A recording layer 2 including an inner recording region 2c, and the transmittance of the seal portion 2d with respect to light of the photosensitive wavelength is equal to or greater than the transmittance corresponding to the end point of the curing reaction of the photocurable organic material. Yes.

  Further, the shape of the hologram recording medium 10 may be a disk shape, but may be a quadrangle when viewed from above as shown in FIG.

  The hologram recording medium 10 is housed in a case that blocks light of the photosensitive wavelength of the recording layer 2, and the case is provided with a shutter that exposes the recording area 2c of the hologram recording medium 10 during recording and reproduction. It is good to have.

3 to 5 show other configuration examples of the hologram recording medium of the present invention.
The hologram recording medium 20 shown in FIG. 3 includes a seal portion 2d between the two transparent substrates 1 in which the photocurable organic material is cured in a region corresponding to the outer edge portion of the hologram recording medium 20, and the outer edge portion. 2 is the same as the hologram recording medium 10 shown in FIG. 2 in that the recording layer 2 including the inner recording region 2c is provided, but in addition, recording is performed on the surface of the transparent substrate 1 facing the recording layer 2. A protective layer 3 for preventing the deterioration of the layer 2 is provided.

Examples of the material constituting the protective layer 3 include SiO ₂ , Si ₃ N ₄ , polyvinyl alcohol (PVA), ethylene-vinyl alcohol copolymer resin (EVOH), and an acrylic hard coat material.

  The hologram recording medium 30 shown in FIG. 4 includes a seal portion 2d between the two transparent substrates 1 in which the photocurable organic material is cured in a region corresponding to the outer edge portion of the hologram recording medium 30, and the outer edge portion. As shown in FIG. 3, the recording layer 2 including the inner recording region 2c is provided, and the protective layer 3 for preventing the recording layer 2 from being deteriorated is provided on the surface of the transparent substrate 1 facing the recording layer 2. Although it is the same as the hologram recording medium 20, in addition to this, a protective layer 4 for preventing damage to the transparent substrate 1 is provided on the surface of the transparent substrate 1 opposite to the recording layer 2. The material constituting the protective layer 4 may be the same as the material used for the protective layer 3.

  The hologram recording medium 40 shown in FIG. 5 includes a seal portion 2d between the two transparent substrates 1 in which the photocurable organic material in a region corresponding to the outer edge portion of the hologram recording medium 30 is cured, and the outer edge portion. What is the recording layer 2 of the transparent substrate 1 is a protective layer 3 that includes a recording layer 2 composed of an inner recording region 2c and prevents the recording layer 2 from deteriorating on the surface of the transparent substrate 1 facing the recording layer 2. 4 is the same as the hologram recording medium 30 shown in FIG. 4 in that the protective layer 4 for preventing damage to the transparent substrate 1 is provided on the opposite surface, but in addition to the recording layer 2 of the transparent substrate 1 An antireflection film 5 is provided on the protective layer 4 on the opposite surface.

Examples of the material constituting the antireflection film 5 include dielectric materials such as SiO ₂ , TiO ₂ , Ta ₂ O ₅ , MgF ₂ , MgO, Al ₂ O ₃ , ZnS, ITO, Si, and Ge. Examples of the system material include fluorinated epoxy resin (for low refractive index) such as Cytop, fine particle TiO ₂ dispersed epoxy resin (for high refractive index), oxetane, UV curable resin, EVOH and the like. Alternatively, the antireflection film 5 may be formed by forming a fine cone shape by fine processing.

  As described above, the protective films 3 and 4 and the antireflection film 5 shown in FIGS. 3 to 5 may be formed on the transparent substrate 1 before the recording layer 2 is formed. Alternatively, the protective film 4 and the antireflection film 5 on the outer surface side of the transparent substrate 1 may be provided after the recording layer 2 is formed between the transparent substrates 1.

  Here, an example will be described in which the exposure processing of the photocurable organic material layer 2a in Step S12 is performed in the method for manufacturing a hologram recording medium of the present invention.

Specifically, as shown in FIG. 1 (b), one transparent to the photocurable organic material layer 2a containing a monomer, a curing initiator, and a sensitizing dye sandwiched between two transparent substrates 1 is used. While monitoring the transmittance of the green light with the transmittance measuring device E arranged on the substrate 1 side (lower side in the figure), green light (wavelength) using the LED as a light source from the other transparent substrate 1 side (upper side in the figure) 530 nm) was irradiated while changing the exposure amount to prepare a hologram recording medium sample.
Next, the obtained sample was pressed at a constant pressure in the direction of compressing the recording layer in the thickness direction, and the length of the photocurable organic material protruding from between the transparent substrates 1 at the end of the sample was measured as a leakage amount.

The above results are shown in FIG.
FIG. 6 shows the relationship between the exposure amount-transmittance at the exposure LED wavelength, and the exposure amount-the amount of leakage of the photocurable organic material from the sample edge.
Here, since the photocurable organic material is exposed and cured as the exposure amount increases, the amount of protrusion (leakage amount) of the photocurable organic material tends to decrease, and at a certain exposure amount (200 in the figure). The amount of leakage became almost zero and became constant thereafter. On the other hand, the transmittance tends to increase as the exposure amount increases, and the transmittance at the time when the leakage amount reaches 0 (35% in the figure) is the minimum exposure required for the curing reaction of the photocurable organic material. The transmittance corresponds to the amount.

  Therefore, the transmittance when the leakage amount reaches 0 is determined as the reference transmittance, and the transmittance is monitored during the exposure processing of the photocurable organic material layer 2a in the step S12. If the exposure process is performed until the point when the reference transmittance is reached, the predetermined region of the photocurable organic material layer 2a can be reliably cured, and a highly reliable seal portion 2d can be obtained.

It is the schematic which shows the manufacturing process of a hologram recording medium. It is the schematic which shows the structure of the hologram recording medium which concerns on this invention. It is the schematic (1) which shows another structure of the hologram recording medium which concerns on this invention. It is the schematic (2) which shows another structure of the hologram recording medium which concerns on this invention. It is the schematic (3) which shows another structure of the hologram recording medium which concerns on this invention. It is a figure which shows the relationship between the exposure amount-the transmittance | permeability, and the leakage amount in the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2 ... Recording layer, 2a ... Photocurable organic material layer, 2b ... Hardened layer, 2c ... Recording area, 2d ... Sealing part, 3, 4 ... Protective layer, 5 ... Antireflection film, 10, 20 , 30, 40 ... Hologram recording medium, E ... Transmittance measuring device, G ... Light source, L _E ... Visible light, L _T ... Transmitted light

Claims (10)

After forming a recording layer made of a photocurable organic material containing a monomer, a curing initiator, and a sensitizing dye on a transparent substrate, the recording layer corresponding to the outer edge of the hologram recording medium is exposed to light having a photosensitive wavelength. A method for producing a hologram recording medium comprising a sealing portion forming step of forming a region for curing a photocurable organic material and sealing a photocurable organic material in an inner region from the outer edge portion,
In the sealing portion forming step, the exposure is performed while measuring the transmittance of the light to be exposed in the recording layer, and the measured light transmittance corresponds to the end point of the curing reaction of the photocurable organic material. A method for manufacturing a hologram recording medium, characterized in that the exposure is terminated at a time when the ratio becomes equal to or greater than the rate.   2. The method of manufacturing a hologram recording medium according to claim 1, wherein the light used for exposure in the sealing portion forming step uses a light emitting diode as a light source. In a hologram recording medium comprising a recording layer made of a photocurable organic material containing a monomer, a curing initiator that is sensitized at a predetermined wavelength, and a sensitizing dye on a transparent substrate,
The recording layer includes a seal portion in which a photocurable organic material in a region corresponding to the outer edge portion of the hologram recording medium is cured and a recording region inside the outer edge portion, and transmits the light of the photosensitive wavelength through the seal portion. A hologram recording medium, wherein the rate is equal to or higher than the transmittance corresponding to the end point of the curing reaction of the photocurable organic material.   After forming a recording layer made of a photocurable organic material containing a monomer, a curing initiator, and a sensitizing dye on a transparent substrate, the recording layer corresponding to the outer edge of the hologram recording medium is exposed to light having a photosensitive wavelength. A seal portion forming step of forming a region for curing the photocurable organic material to seal the photocurable organic material in the inner region from the outer edge portion, and in the seal portion forming step, the recording layer of the light to be exposed The hologram recording medium which performs the exposure while measuring the transmittance at, and terminates the exposure when the measured light transmittance is equal to or higher than the transmittance corresponding to the end point of the curing reaction of the photocurable organic material. A hologram recording medium manufactured by a manufacturing method.   The hologram recording medium according to claim 3, wherein the transparent substrate is a glass substrate.   The hologram recording medium according to claim 3, wherein the transparent substrate is a polycarbonate film.   The hologram recording medium according to claim 6, wherein the birefringence amount of the transparent substrate is 30 degrees or less as a phase difference (absolute value) with respect to light transmitted in the thickness direction of the substrate.   5. The hologram recording medium according to claim 3, further comprising a protective layer for preventing the recording layer from being deteriorated on a surface of the transparent substrate on the recording layer side.   The hologram recording medium according to claim 3, further comprising a protective layer for preventing damage to the transparent substrate on a surface of the transparent substrate opposite to the recording layer.   The hologram recording medium according to claim 3, further comprising an antireflection film on a surface of the transparent substrate opposite to the recording layer.

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