JPH0289080A - Method for generating reflection hologram - Google Patents

Abstract

PURPOSE:To reduce the diffraction efficiency of a ghost hologram and to improve that of a reflection hologram by setting an intensity ratio of reference light to object light to a desired value larger than one. CONSTITUTION:An intensity ratio R/O of reference light R to object light 0 is set to >1. Consequently, even if reflected light (a) on a boundary surface A-A' exists, its efficiency is approximately 0, and it does not practically reach generation of the ghost hologram. Preferably, an antireflection film 17 is provided on the lower face (the face opposite to a photosensitive material 13) of a glass substrate 11 for into purpose of eliminating the reflected noise light on a boundary surface C-C'. That is, the reflected noise light is eliminated. Thus, the diffraction efficiency of the ghost hologram is reduced and that of the reflection hologram is improved.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for creating a reflection hologram, the purpose is to prevent or suppress the generation of ghost holograms that would otherwise occur when creating a reflection hologram, and to When exposing a holographic dry plate coated with a photoresist film by causing two coherent beams (reference beam and object beam) to interfere with each other from both sides, the intensity ratio between the intensity R of the reference target and the intensity 0 of the object beam is R10>1. Configure it so that

[Industrial Field of Application] The present invention relates to a method for creating a reflection hologram by interfering and exposing two types of coherent light from both sides of a hologram dry plate.

[Conventional technology]

A reflection hologram is formed by entering a reference wave and an object wave from both sides of a substrate coated with a photosensitive agent (emulsion) on one surface, interfering with each other, and exposing the substrate.

At this time, there is a problem in that an undesirable ghost hologram is generated in addition to the original reflection hologram.

First, let's talk about the cause of this ghost hologram.
．． This will be explained with reference to FIG.

In FIG. 9, a glass substrate (for example, refractive index n=1.
5) Emulsion (for example, n=1.6) on one side of 11
Coherent reference light R and object light 0 are irradiated from both sides of the hologram dry plate 10 coated with. In the figure, reference light R
is irradiated from the emulsion 13 side, and object light 0 is irradiated from the substrate 11 side. A reflection hologram (interference fringes) is formed by interference between the reference beam R and the object beam O. The interference fringes in this case extend in the direction of the road surface of the emulsion.

[Problem to be solved by the invention]

However, the interface between the air layer (n=1.0) and the emulsion 13 is A-A', and the interface between the emulsion 13 and the glass substrate 11 is B-.
B'' and the interface c-c' between the glass substrate 11 and the air layer
Reflected light (e.g. from the mouth, etc.) is generated, and interference occurs between these reflected lights and two interference lights (object light and reference light).
This creates a ghost hologram. In particular, it has been confirmed that the ghost hologram caused by the interference between the reflected light aperture at the boundary surface A-A'' and the refracted light ■ of the reference beam R has the most adverse effect.As is clear from the figure, the ghost hologram Because it is caused by light, it is not a reflection type hologram, but a transmission type hologram due to interference with the reference light from the same direction.In other words, when the emulsion 13 is viewed in cross section as shown in FIG. A lying reflection hologram 30 and a ghost hologram 31 lying in the thickness direction thereof are formed in an intersecting state.

Conventionally, the intensity ratio R10 between the reference light R and the object light O is generally approximately equal to l (R10ζ1.0). That is, the reference light and the object light are made to enter with substantially the same light intensity (to optimize the contrast, as will be described later).

[Means to solve the problem]

The inventors of the present invention have experimentally confirmed that by increasing the R10 ratio to greater than 1, the occurrence of the ghost hologram described above can be suppressed. That is, it has been found that by making the intensity of the reference target greater than the intensity of the object light, the interference conditions for ghost holograms are broken, and ghost holograms are hardly generated.

However, if the R10 ratio is not equal to 1, the sharpness (contrast) of the exposure distribution decreases (the third
(see figure). This is exactly why the R10 ratio is conventionally set to 1. Therefore, in the present invention, it is necessary to compensate for the decrease in sharpness (■) when setting the R10 ratio to be greater than 1.

A small sharpness means that the refractive index modulation component Δn becomes small. These relationships are 2.3.
As shown in the figure. Incidentally, such a characteristic curve itself is well known.

FIG. 2 shows the relationship between the refractive index n and exposure 31E, and FIG. 3 shows the relationship between sharpness and R10 ratio. From Figure 3, the sharpness ■ is maximum (■=1) when R10=1, and R1
It can be seen that the ratio decreases as the 0 ratio becomes larger than 1. It can also be seen that the visibility V and the refractive index modulation component Δn have a substantially proportional relationship.

Generally, in order to obtain high diffraction efficiency of a hologram, the thickness t of the hologram must satisfy t≧ ψ・λ・COSθ8/Δn (where ψ is a constant and approximately equal to π. θ is the Bragg angle) It is known.

Therefore, the relationship between R10 ratio and Δn is determined in advance from Figure 2.3 (from Figure 3, the relationship between R10 ratio and sharpness ■ is determined, and from Figure 2, the relationship between ■ and Δn is determined). Because we can find
As a result, the relationship between the R10 ratio and Δn is determined), thereby making it possible to set the necessary hologram thickness (thickness of the photosensitive agent). In this way, even if Δn becomes small because the R10 ratio is greater than 1, the hologram thickness conditions necessary to obtain high diffraction efficiency can be set, and there is no problem in practice.

That is, according to the first feature of the present invention, the configuration is characterized in that the intensity ratio between the intensity R of the reference wave and the intensity O of the object wave is set so as to satisfy R10>1.

Preferably, 4≦R/O≦16.

Preferably, the surface of the hologram dry plate opposite to the photoresist film is coated with an antireflection film in advance.

In addition, since reflection holograms and ghost holograms (transmission holograms) have different dependence of their diffraction efficiency on film thickness, by utilizing this property, it is possible to ensure high efficiency of reflection holograms and at the same time reduce the efficiency of ghost holograms. Preferably, it can be suppressed to substantially zero. The film thickness conditions for obtaining high efficiency in the reflection hologram are as described above. On the other hand, the condition for making the efficiency of the ghost hologram 0 is L=mλcosθa/Δn.

(However, m is a positive integer). From the above, the conditions for increasing the efficiency of the reflection hologram and making the efficiency of the ghost hologram O are as follows.

That is, according to another feature of the present invention, the exposure conditions (intensity ratio of interference light, exposure amount, bias exposure, etc.) and processing conditions are adjusted such that the structural parameters of the reflection hologram and the ghost hologram satisfy the above expressions. Set.

[For production]

The intensity ratio of the reference wave intensity R and the object wave intensity 0 is R10>
If it is set to 1, the interference conditions are broken and the generation of ghost holograms is prevented or significantly suppressed.

In particular, it has been experimentally confirmed that when the range is 4≦R/O≦16, a sharpness that poses no problem in practical use can be ensured.

Furthermore, high diffraction efficiency can be ensured by setting the film thickness t of the photosensitive agent layer to satisfy ψ·λ·cos θ, ≦(Δn−t).

Furthermore, if the structural parameters of the desired reflection hologram to be formed and the transmission ghost hologram formed by the reflection noise light are set to satisfy the following, the generation of ghost holograms can be similarly prevented or suppressed. The process of deriving the above equation will be clarified in the Examples section below.

〔Example〕

FIG. 1 shows a first embodiment of the present invention. Basically, it is the same as that shown in FIG. 9, but according to the present invention, the intensity ratio R/O between the reference light R and the object light 0 is greater than 1, preferably 4≦R/O≦16. is set to By doing so, even if there is a reflection light aperture at the interface A-A', its efficiency is almost equal to 0, and therefore a ghost hologram is not substantially created.

Preferably, an antireflection film (AR coat) 17 is applied to the lower surface of the glass substrate 11 (the surface opposite to the photosensitive material 13) in order to remove reflected noise light at the interface c-c'. That is, the reflected noise light A in FIG. 9 has been removed. Incidentally, the interference light for creating the original reflection hologram is ■ and ■.

As can be seen from FIG. 2, when the R10 ratio is β, the contrast ■ is given by:

Also, the upper limit (16) and lower limit (4
) have been confirmed experimentally, and it has been confirmed that the sharpness (2) is a value that can be used practically when it is within this range.

Figure 4.5 shows the effects of the present invention.

FIG. 4 shows the case of exposure with an R10 ratio of approximately 1 (R10ζ1), that is, corresponds to the prior art. In this case, the reflection hologram (
The diffraction efficiency of the first-order reflected light remains at about 60%. On the other hand, as shown in FIG. 5, in the case of exposure with R10ζ4, the diffraction efficiency of the ghost hologram decreases as described above, so that the diffraction efficiency of the reflection hologram increases to about 90%. Note that the values of each parameter in the experiment are as shown in the figure. In addition, when R10>1, although the absolute value of efficiency changes, in both cases the conventional (R10
It was confirmed that the diffraction efficiency was better than that of -1).

As described above, according to the present invention, the diffraction efficiency of a ghost hologram (transmission type hologram) can be made so small that it can be practically ignored, and as a result, the diffraction efficiency of a reflection type hologram can be greatly improved. .

FIG. 7 shows the relationship between the film thickness t and relative efficiency in a reflection hologram, and FIG. 8 similarly shows the relationship between the film I\t and relative efficiency in a transmission hologram (ghost hologram). As is clear from these figures, the efficiency of holograms greatly depends on the film thickness t, so by utilizing this property, as mentioned above, high efficiency can be ensured with reflection holograms, while on the other hand, the efficiency of ghost holograms can be substantially reduced. It is possible to set conditions such as setting the value to 0.

According to Ogelnik's theory, the diffraction efficiency η of a hologram is given by: for a reflection hologram, and for a transmission hologram. However, λ is the reproduction wavelength, t is the film thickness, Δn is the refractive index modulation component, θ is the Bragg angle (the reproduction angle at which the maximum efficiency is obtained), and the subscripts R1T refer to the reflection hologram and transmission hologram, respectively. represents that

From equation (1), if X≧π, η≧0.996(99,
6%)...(3) From formula (2), if x = mπ (m: natural number), η = 0.0
(0,0%) ...(4) is obtained.

In order for the film thickness condition that satisfies equation (4) to also satisfy equation (3) at the same time, the following equation needs to hold.

The parameters Δn and θ in the above equation are optimally determined depending on the hologram design, exposure conditions, etc. Incidentally, exposure processing, etc. should be carried out in consideration of deviations of various parameters from design values due to swelling and shrinkage of the emulsion layer.

Figures 6A and 6B show the effects of the present invention. Figure 6A shows the formula (
5) when m=1. In this case, cosθRζc
Since it can be regarded as osθ1, Δn, ≧Δn.

Therefore, in the experiment, Δn, ζΔny
': Exposure and processing were performed so that the ratio was 0.05.

The film thickness t is t = λ cos θ, /ΔnT, λ = 0.4765
μm.

By substituting cos θ, '=;1.0 and Δnt=0.05, t4:i9.5 μm was obtained. A reflection hologram created in this way had a diffraction efficiency of over 80%.

On the other hand, in a reflection hologram that was intentionally exposed and processed so that Δn<Δn for reference, the diffraction efficiency remained at about 60%, as shown in FIG. 6B.

In this way, by performing exposure and processing so that the design parameters of the reflection hologram and ghost hologram satisfy the above-mentioned predetermined relationships, it is possible to prevent the transfer of light energy to the ghost hologram and achieve the desired diffraction efficiency of the reflection hologram. It can be increased to over 80%.

(Effects of the Invention) As described above, according to the present invention, by designing the intensity ratio of the reference light and the object light to a desired value of 1 or more, or by adjusting the film thickness of the photosensitive agent layer under the above-mentioned specific conditions. The efficiency of the ghost hologram can be reduced by placing the reflection hologram at a lower temperature, and as a result, the efficiency of the reflection hologram can be greatly increased.

Further, according to the present invention, the efficiency of the ghost hologram is reduced by designing the structural parameters of each of the reflection hologram and the ghost hologram to satisfy the above-mentioned specific conditions. can be significantly increased.

[Brief explanation of the drawing]

FIG. 1 shows a method for creating a reflection hologram according to the present invention.
An illustrative diagram showing an example, FIG. 2 is a characteristic diagram showing the relationship between refractive index and exposure amount, FIG. 3 is a characteristic diagram showing the relationship between sharpness and R10 ratio, and FIG. 4 is a characteristic diagram showing the relationship between sharpness and R10 ratio. FIG. 5 is a characteristic diagram showing the diffraction efficiency in the case of R10ζ4.
Characteristic diagram showing the diffraction efficiency in the case of 0 (present invention), No. 6A
The figure is a characteristic diagram of diffraction efficiency showing the effect of the present invention, Figure 6B is a characteristic diagram of diffraction efficiency under conventional conditions for comparison with Figure 6A, and Figure 7 is the film thickness of the reflection hologram. Figure 8 is a diagram showing the relationship between film thickness and relative efficiency of a transmission hologram, Figure 9 is a diagram illustrating the conventional method for creating a reflection hologram. FIG. 10 is an illustrative diagram for explaining the existence of ghost holograms. IO... Hologram dry plate, 11... Substrate, 13... Photosensitive agent.

Claims (1)

[Claims] 1. A reflection type hologram in which two coherent beams (reference beam, object beam) are interfered and exposed from both sides of a hologram dry plate (/O) in which a photoresist film (13) is coated on a substrate (11). In the creation method, the intensity of the reference light is R and the intensity of the object light is O.
A method for creating a reflection hologram, the method comprising: setting the intensity ratio R/O of the two to be R/O>1. 2. The production method according to claim 1, wherein the intensity ratio R/O is set in a range of 4≦R/O≦16. 3. The manufacturing method according to claim 1, wherein the surface of the hologram dry plate opposite to the photosensitive film is coated with an antireflection film (17) in advance. 4. The thickness t of the photoresist film satisfies the following formula: φ・λ・cosΘ_B≦(Δn・t) However, Δn: refractive index modulation component λ: reproduction light wavelength Θ_B: Bragg angle φ: constant (>0) The method according to claim 1, characterized in that: 5. In a method for creating a reflection hologram in which two coherent beams (reference beam, object beam) are exposed from both sides of a hologram dry plate coated with a photosensitive film on a substrate, the desired reflection hologram and reflection noise to be formed are determined. A method for creating a reflection hologram characterized in that each structural parameter of a transmission ghost hologram formed by light is set to satisfy the following formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (m = 1, 2, 3・
(...) However, the subscripts R and T indicate parameters related to the reflection hologram and ghost hologram, respectively, Δn indicates the refractive index modulation component, and Θ indicates the Bragg angle.