JPH07114329A - Hologram recording method and hologram recording material - Google Patents

Abstract

(57) [Abstract] [Purpose] A hologram recording method and a hologram recording material in which unwanted interference fringes do not occur and a hologram does not whiten. When two holograms are incident on a hologram recording material 20 in which a photosensitive material layer 3 is provided on the flexible films 1 and 2 to record hologram interference fringes, the flexible films 1 and 2 at the hologram recording wavelength are exposed to light. The reflection occurring at the interface due to the difference in the refractive index of the material layer 3 is 0.1% by selecting the refractive index of the flexible films 1 and 2 and the photosensitive material layer 3 and the polarization direction of the incident light beam at the time of hologram recording. It is reduced to the following to reduce generation of undesired interference fringes due to interface reflection. Further, it is desirable that the optical lengths of the retardation and the center line average roughness of the flexible films 1 and 2 be 25% or less of the hologram recording wavelength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram recording method and a hologram recording material, and more particularly to a hologram recording material in which unwanted interference fringes and whitening are reduced.

[0002]

2. Description of the Related Art In recent years, holograms have come to be widely used for decoration, forgery prevention, optical elements, and the like. In particular, recently, volume phase having excellent wavelength selectivity and excellent three-dimensional appearance has been obtained. Type (Lippmann type) holograms are drawing attention.

For example, the hologram combiner is one optical element, and its function can be said to be a semi-transmissive imaging element. FIG. 6A is a diagram for explaining the photographing method, in which the light oscillated from the laser 10 is divided into two by the half mirror 11, and each laser light is divided by the lens 1.
A holographic combiner is a system in which the divergent light emitted from one point is changed at 2 and 13 and these two divergent lights are made incident from both sides of the volume phase hologram recording material 14 such as a photopolymer and interference recorded as a Lippmann hologram.

Such a hologram combiner 4 is
As shown in (b) of the figure, light emitted from the display body 15 installed near one of the divergence points at the time of photographing is diffracted in the reflection direction,
The diffraction is performed as if it came out of the display body image 15 'installed near the other divergent point at the time of photographing, and the image forming magnification and the image position are the divergent point at the time of photographing and the recording material 14.
It is determined by the relative distances L and L'of each other, and only the light of the wavelength at the time of recording or a wavelength having a specific relationship with it is diffracted, and the light of other wavelengths is transmitted, so that the images can be superimposed or combined. is there. As a hologram optical element represented by such a hologram combiner, there is a combiner for head-up display and the like.

By the way, the above-mentioned volume phase hologram recording light-sensitive material is usually made of PET, as shown in the cross section of FIG.
A flexible film 2 such as (polyethylene terephthalate) coated with a photosensitive material 3 such as a photopolymer is used. In FIG. 1, another flexible film 1 is attached on the photosensitive material 3 so as to form a dry film.

[0006]

However, in the above-mentioned conventional technique, when hologram recording is performed on a film having a configuration as shown in FIG. 1, unwanted interference fringes (grain pattern, contour line) are formed in the hologram photosensitive material 3. , Or stripes) are recorded, and the phenomenon that the hologram looks white (whitening) is observed.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide a hologram recording method and a hologram recording material which do not cause unwanted interference fringes and do not cause whitening of holograms. Is to provide.

[0008]

As a result of various studies to solve the above problems, by selecting the refractive index of the flexible film provided in contact with the hologram light-sensitive material layer and the polarization direction of the laser beam during hologram recording. By using a flexible film with little birefringence,
The present invention has been completed by finding that the generation of undesired interference fringes (wood grain shape, contour line shape, stripe shape) can be reduced, and whitening can be reduced by using a flexible film having high smoothness. It is a thing.

That is, the hologram recording method of the present invention is a hologram recording method in which two light beams are incident on a hologram recording material provided with a photosensitive material layer on a flexible film to record hologram interference fringes. The reflection that occurs at the interface due to the difference in the refractive index between the flexible film and the photosensitive material layer is determined by selecting the refractive index of the flexible film and the photosensitive material layer and the polarization direction of the incident light beam during hologram recording. % Or less to reduce the generation of undesired interference fringes due to interface reflection.

In this case, it is desirable to reduce the occurrence of undesired interference fringes due to birefringence by using a flexible film having a retardation of 25% or less of the hologram recording wavelength.

Furthermore, by using a flexible film having a center line average roughness of 25% or less of the hologram recording wavelength in terms of optical length, it is possible to reduce the whitening of the hologram caused by irregular reflection due to surface irregularities. Is desirable.

Further, the hologram recording material of the present invention is a hologram recording material in which a photosensitive material layer is provided on a flexible film, and the reflectance at the hologram recording wavelength at the interface between the flexible film and the photosensitive material layer is 0.1. The combination of the refractive indexes of the flexible film and the photosensitive material layer is selected so as to be not more than%.

In this case, the retardation of the flexible film is preferably 25% or less of the hologram recording wavelength.

The center line average roughness of the flexible film is preferably 25% or less of the hologram recording wavelength in terms of optical length.

[0015]

In the present invention, by selecting the refractive index of the flexible film and the photosensitive material layer and the polarization direction of the incident light beam during hologram recording, the interface between the flexible film and the photosensitive material layer at the hologram recording wavelength is selected. Since the reflection that occurs is reduced to 0.1% or less, it is possible to reduce the generation of unwanted interference fringes due to interface reflection,
A high quality hologram can be obtained.

[0016]

EXAMPLES The hologram recording method and hologram recording material of the present invention will be described below based on several examples. The hologram recording film 20 according to the present invention is shown in FIG.
It is made with a layer structure as shown in the cross section. here,
The flexible films 1 and 2 are support films that are usually used for dry film type hologram photosensitive materials, and PET, triacetyl cellulose, polyvinyl chloride, polyethylene, PMMA (polymethyl methacrylate) and the like can be used. . As the hologram sensitive material 3, a conventionally known volume sensitive and phase sensitive material such as a photopolymer for hologram recording can be used in the present invention. The layer structure as shown in FIG. 1 is obtained by printing the hologram photosensitive material 3 on the flexible film 2 by a known coating method such as gravure coating, roll coating, blade coating, die coating, and the like, and further forming another layer thereon. It can be obtained by laminating the flexible film 1 of.
The flexible film 1 may be omitted.

Now, a case where the hologram recording film 20 as described above is used and hologram recording is performed by arranging the two light fluxes 21 and 22 from both surfaces in the arrangement as shown in FIG. 2 will be considered. In FIG. 2, glasses 24, 24 are arranged on both sides of the hologram recording film 20 via index matching liquids (IMF) 23, 23.

First, let us consider reflection at the interface when the polarization of the laser light is vertical and horizontal with respect to the incident surface. Assuming that the material of each layer and the refractive index (n _{0 to} n ₈ ) are as shown in FIG. 2, the incident angle to each interface,
The refraction angles (i _{0 to} i ₈ ) are defined as shown. From the law of refraction, n ₀ sin i ₀ = n ₁ sin i ₁ = ... = c (constant). From the Fresnel equation, regarding the polarization component in the incident plane, if the amplitude of the incident light is E _p and the amplitude of the reflected light is R _p , For the polarization component perpendicular to the plane of incidence, Is.

Therefore, regarding the laterally polarized light component, For the vertical polarization component, From the above formula, the reflectance (R ² ) at the interface between the layers can be calculated. The values calculated for the reflectance at each interface at an incident angle of 45 ° and 60 ° are shown in (Table-1). Here, the refractive index of each layer is set to a value shown in (Table-1).

[0020]

In this (Table 1), the reflection of the interface between the glass and the air is caused by the antireflection coating (AR) on the surfaces of the glass 24, 24.
It has already been known that by applying a coating, it can be reduced to practical use. Further, by selecting the refractive index of the index matching liquid (IMF) 23, 23, it is possible to reduce the reflection at the interface adjacent to the IMF 23, 23.

However, in this case, the refractive index difference between the flexible films 1 and 2 and the photosensitive material 3 (FIG. 1) is an absolute problem.

The sensitive material 3 has a refractive index of 1.50, the flexible films 1 and 2 have different refractive indexes in the vicinity thereof, and
When the angles of incident light are 45 ° and 60 °, the values of the above equations are calculated (Table 2).

[0024] 3 and 4 are graphs of the results of the above (Table-2).
Is. It can be seen from FIGS. 3 and 4 that the use of the P wave has a relatively small reflectance even if the difference in refraction at the interface is large.

Next, in the case of using several flexible films 1 and 2 having different refractive indexes as shown in (Table 3), it was examined whether or not undesired interference fringes were generated (of the photosensitive material 3). The refractive index was 1.50.). The hologram recording was performed using S waves. As a result, (Table-
As described in 3), the reflectance at the interface is 0.1%.
In the following cases, no generation of undesired interference fringes was observed. The pattern of the generated unwanted interference fringes is shown in FIG.
It is composed of light and dark patterns such as wood grain and contour lines as shown in (a) and (b). This is a so-called equal-thickness interference fringe that accompanies a change in film thickness on the surfaces of the films 1 and 2. Film 1,
If 2 is strictly flat, parallel interference fringes of equal pitch, which can be seen in repeated reflection, should occur, but the actual film has some thickness unevenness, and the film thickness is If the recording thickness changes by ½ or more of the recording wavelength, the light and dark will be reversed, resulting in the complicated pattern as described above. If the photosensitive material 3 and the films 1 and 2 have the same or substantially the same refractive index, this interface is the same as that which is optically absent, and thus unnecessary interference fringes do not occur. Flexible film 1 such that the reflectance at the interface is 0.1% or less in reflectance,
By selecting the combination of 2 and the photosensitive material 3, it is possible to substantially eliminate unnecessary interference fringes. In the case of (Table-1), PET is used as the material for the flexible films 1 and 2.
It can be seen that polyvinyl chloride, polyethylene, polymethylmethacrylate, or triacetyl cellulose may be used instead of.

[0026] .

Next, the influence of the birefringence of the flexible films 1 and 2 will be examined. When light passes through a birefringent material, it splits into two polarizations that give different velocities, and thus different indices of refraction. The vibration directions of these polarized lights are at right angles to each other. When the refractive index differs depending on the direction, when linearly polarized light that oscillates in a direction that is neither parallel nor perpendicular to the optical axis is incident, a two-component wave that oscillates in the sample in the direction parallel to the optical axis and the direction perpendicular to it Divided and proceed. Now, assuming that the refractive index in vacuum is 1, the refractive index of the component in the direction parallel to the optical axis is n, the refractive index in the direction perpendicular to the optical axis is n, and the wavelength of the laser light used for recording is λ. , The wavelength in the direction parallel to the optical axis and the wavelength in the direction perpendicular to the optical axis are λ / n∥ and λ / n⊥, respectively, so the phase difference δ when passing through the sample of thickness d is (1 / 2π) .delta. = D. (N.parallel.-n.perp.) /. Lambda. =. GAMMA./.lambda..differential..GAMMA.=d.(n.parallel.-n.perp.). Here, Γ is the retardation.

Brightness and darkness are inverted when the phase difference δ = π, but as can be seen from this equation, it is presumed that there is an allowable value in the birefringence of the flexible films 1 and 2. Hologram recording is performed using several flexible films 1 and 2 with different retardations.
The presence or absence of generation of unnecessary interference fringes was observed. The results (Table-
4).

[0029] Note) Recording wavelengths of 458nm, 578nm, 647n
m was used. The λ / 4 are 114 nm and 1 respectively.
44 nm and 162 nm.

As shown in Table 4, when the retardation was 25% (λ / 4) or less of the wavelength, undesired interference fringes were not observed. The pattern of undesired interference fringes due to the retardation was a stripe-shaped bright and dark pattern as shown in FIG.

Further, the influence of the smoothness of the flexible films 1 and 2 will be examined. If the smoothness of the films 1 and 2 is insufficient, light scattering occurs due to the unevenness of the surface, and this becomes stray light and is recorded in the hologram, and the hologram appears whitish. The value of this unevenness can also be optically measured as a haze value. It is estimated that there is a range that can be regarded as being substantially optically flat if there are few irregularities of a certain wavelength or more of the light wavelength.
Table 5 shows the results of samples with various centerline surface roughnesses (Ra values).

[0032] Note) Recording wavelengths of 458nm, 578nm, 647n
m was used. The λ / 4 are 114 nm and 1 respectively.
44 nm and 162 nm.

From the results shown in Table 5, the whitening of the hologram did not occur when the optical thickness of the center line surface roughness (Ra value) was 25% (λ / 4) or less of the wavelength.

The hologram recording method and hologram recording material of the present invention have been described above based on the embodiments.
The present invention is not limited to these examples, and various modifications are possible.

[0035]

As is apparent from the above description, according to the hologram recording method and hologram recording material of the present invention, the refractive index of the flexible film and the photosensitive material layer,
Also, by selecting the polarization direction of the incident light flux during hologram recording, the reflection occurring at the interface between the flexible film and the photosensitive material layer at the hologram recording wavelength is 0.1.
%, The generation of undesired interference fringes due to interface reflection can be reduced, and a high quality hologram can be obtained.

In the present invention, the use of a flexible film having low birefringence and high smoothness can further reduce the generation of unwanted interference fringes and reduce the whitening of holograms. It is possible to obtain a combiner suitable for an excellent head-up display application.

The present invention is not limited to combiners for head-up displays, but is also applicable to volume phase type (Lippmann type) holograms for decoration, anti-counterfeiting and other optical elements that require high appearance quality. can do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a layer structure of a hologram recording film according to the present invention.

FIG. 2 is a cross-sectional view showing an arrangement for hologram recording using the film of FIG.

FIG. 3 is a diagram showing the relationship between the refractive index and the reflection at the interface when the incident angle is 45 °.

FIG. 4 is a diagram showing the relationship between the refractive index and the reflection at the interface when the incident angle is 60 °.

FIG. 5 is a diagram showing a pattern of undesired interference fringes.

FIG. 6 is a diagram for explaining an image capturing method and operation of the hologram combiner.

[Explanation of symbols]

 1, 2 ... Flexible film (supporting film) 3 ... Holographic material 20 ... Hologram recording film 21, 22 ... Luminous flux 23 ... Index matching liquid 24 ... Glass

Claims (6)

[Claims] 1. A hologram recording method in which two light beams are incident on a hologram recording material having a photosensitive material layer provided on a flexible film to record hologram interference fringes, the flexible film and the photosensitive material layer at a hologram recording wavelength. Reflection that occurs at the interface due to the difference in the refractive index of, the refractive index of the flexible film and the photosensitive material layer,
A hologram recording method, wherein the polarization direction of an incident light beam during hologram recording is selected to be 0.1% or less to reduce the generation of undesired interference fringes due to interface reflection. 2. The hologram according to claim 1, wherein the occurrence of unwanted interference fringes due to birefringence is reduced by using a flexible film having a retardation of 25% or less of a hologram recording wavelength. Recording method. 3. The use of a flexible film having a center line average roughness of 25% or less of a hologram recording wavelength as an optical length reduces the whitening of a hologram caused by irregular reflection due to surface irregularities. The hologram recording method according to claim 1 or 2, which is characterized in that. 4. A hologram recording material having a photosensitive material layer provided on a flexible film, wherein the reflectance is 0.1% or less at the hologram recording wavelength at the interface between the flexible film and the photosensitive material layer. A hologram recording material, characterized in that a combination of refractive indices of a film and a photosensitive material layer is selected. 5. The hologram recording material according to claim 4, wherein the retardation of the flexible film is 25% or less of a hologram recording wavelength. 6. The hologram recording material according to claim 4, wherein the center line average roughness of the flexible film has an optical length of 25% or less of a hologram recording wavelength.