JPS63306486A - How to create a hologram - Google Patents

Abstract

PURPOSE:To generate a hologram whose film layer is locally different by preparatorily exposing a substrate except a part, where the film thickness should be increased, before a photosensitizer is subjected to interference exposure for the purpose of recording a desired hologram. CONSTITUTION:Before plural laser luminous fluxes 15 and 17 are projected to a hologram dry plate, where a photosensitizer 33 is coated on a transparent substrate 31, to perform interference exposure, only prescribed parts of the photosensitizer are preliminarily exposed. Since parts of the photosensitizer where the film thickness is locally increased have a relatively small Bragg angle margin DELTAtheta, these parts are caused to correspond to crossing parts of the hologram in a hologram window to improve the selectivity between diffraction and transmission of beam only in crossing parts. Thus, the hologram dry plate is obtained where the photosensitizer whose film thickness is locally different is applied to the substrate, and the hologram characteristic is partially changed on the same face on demand.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The film thickness of a photosensitive agent on a hologram dry plate is partially thickened to make it non-uniform, so that the diffraction efficiency of the hologram is made partially different. As a result, for example, in a hologram window where two band-like holograms intersect, it is possible to have selectivity in beam transmission and diffraction between the intersecting part and other non-intersecting peripheral parts, and the desired Bragg angle margin can be set for each. You can get it. In general, it is possible to meet requirements for the same hologram when the required characteristics differ locally. - In the process of creating a hologram having such a non-uniform film thickness, prior to interference exposure of the photosensitive material to record a desired hologram, preliminary exposure is performed in advance to remove areas where the film thickness should be increased. Therefore, when the photosensitive agent is subjected to interference exposure, the pre-exposed area is no longer exposed to i-rays and no interference fringes are formed. As a result, a hologram is formed in which the portions that were not pre-exposed become thicker.

[Industrial application field]

The present invention relates to holograms, and particularly to hologram dry plates having a substrate coated with a photosensitizer.

Holograms are widely used in barcode league laser scanners, laser scanners for printers, various sensors, and optical equipment.

[Conventional technology]

A hologram is formed by applying a photosensitive agent onto a transparent substrate (glass or acrylic substrate, etc.), using a hologram dry plate, irradiating this with multiple laser beams, and recording the interference fringes on the photosensitive material. . Conventionally, the photosensitizer for such hologram dry plates has a monolayer homogeneous structure, and therefore,
The characteristics of the created hologram were also uniform within the plane. That is, there was no idea of partially varying the characteristics within the same hologram plane.

[Problem that the invention seeks to solve]

Therefore, when locally different characteristics are required within a plane, it is not possible to satisfy the required characteristics in all parts, and priorities are determined based on the greatest common divisor or according to the frequency of use of hologram parts. Design the hologram creation conditions using
We had no choice but to make more or less compromises due to its characteristics.

As mentioned above, as an example where locally different hologram characteristics (diffraction efficiency, etc.) are required within the same plane, for example, the two strips disclosed in Japanese Patent Application No. 61-239903 by the applicant of the present application are examples. An example is a hologram scanner in which holograms are stacked in a crosswise manner. This is because conventional hologram scanners have one
In view of the fact that it required a space on the order of 0 (lem), which hindered the thinning of the device, we created a hologram scanner by stacking two holograms with a transparent substrate interposed between them and eliminating that space. It is designed to be thinner.The feature is that the light diffracted at the intersection (central part) of the upper and lower stacked holograms passes through each other's holograms outside the Bragg angle condition. In other words, the intersecting part, that is, the central part, is required to have high incidence angle selectivity (the incidence angle margin is narrow), while the non-intersecting part, that is, the peripheral part, is required to have high selectivity of the incident angle even if the incident angle is slightly shifted. A wide angle of incidence margin is desirable to obtain high efficiency.

Hereinafter, the hologram scanner disclosed in the above-mentioned prior patent application will be briefly explained with reference to FIGS. 4 to 7.

Note that this is just one example of when it is necessary to locally vary the hologram characteristics within the same plane, which is the premise of the present invention. Since this article is not intended to discuss the structure of the scanner itself, only the main points will be briefly explained.

The hologram window shown in FIG. 4.5 has two diagonally intersecting band-shaped first and second holograms 1 and 2, which are formed on respective transparent substrates 11 and 12. Both holograms 1.2 intersect in their central part. The hologram window has a function of receiving laser scanning light emitted by a rotating mirror (not shown) or the like and diffracting it in a predetermined direction to form a desired scanning pattern. At this time, beams corresponding to the upper and lower patterns near the center are selected based on the following principle.

First, reference is made to FIG. 6, which shows a general characteristic curve of diffraction efficiency and transmittance of a hologram versus incident angle. The diffraction efficiency shown by the solid line is maximum at a predetermined angle of incidence (Bragg angle) B, and the efficiency decreases as it deviates from the Bragg angle B. On the other hand, the transmittance shown by the broken line is minimum at the Bragg angle B, and increases as it deviates from the Bragg angle B. Therefore, in Fig. 4.5, if the Bragg angle at the center (intersection) of the upper second hologram 2 is adjusted to the scanning beam (b), the scanning beam diffracted by the lower first hologram l ( Since the incident angle of the beam (a) is deviated from the Bragg angle B, most of the beam is transmitted through the hologram 2 as shown in FIG. In this way, the holograms 1 and 2 formed above and below can generate an intersecting scanning pattern without interfering with each other.

Therefore, the diffraction efficiency at the intersection near the center of the hologram window is as steep as possible in order to improve the selectivity (separability) between the diffraction of the scanning beam (b) and the transmission of the scanning beam (a). It is desirable that Δθ in the figure be small. On the other hand, since only one beam is incident on the non-intersecting portions, as in the scanning beam (c) in FIG. 4.5, there is no need to provide selectivity in transmission and diffraction as in the intersecting portions. In this case, of course the scanning beam (c)
It is desirable that the margin be large for the error in the angle of incidence, and therefore Δθ in FIG. 9 should be as large as possible.

As described above, in a hologram for a hologram window, the characteristics required for the hologram are different between the central intersecting portion and the peripheral non-intersecting portion.

Conventionally, there was no way to meet such demands at all.

FIG. 7 shows the general relationship between the Bragg angle margin Δθ and the film thickness of the hologram. As is clear from Figure 7, -a
It is known that as the film thickness increases, the margin decreases, and on the contrary, as the film thickness decreases, the margin increases.

Therefore, the present invention attempts to realize locally different hologram characteristics by controlling the film thickness of the hologram using the relationship shown in FIG.

An object of the present invention is to provide a specific method for creating such a hologram having locally different film thicknesses.

[Means for solving problems]

In order to achieve the above object, according to the hologram production method of the present invention, when a hologram dry plate coated with a photosensitizer on a transparent substrate is irradiated with a plurality of laser beams for interference exposure, the photosensitizer is It is characterized in that only a predetermined portion of the image is locally pre-exposed in advance.

[Effect]

As shown in FIG. 7, the Bragg angle margin Δθ is relatively small in the area where the photosensitive agent film thickness is locally thickened, so by making this area correspond to the intersection of the holograms in the hologram window, for example, the intersection area can be reduced. It is possible to improve the selectivity of beam diffraction and transmission.

〔Example〕

Preferred embodiments of the present invention will be described below, mainly with reference to FIGS. 1 to 3.

A hologram dry plate is basically formed by coating a photosensitive agent 33 for hologram recording on a transparent substrate 31 such as glass or acrylic.According to the features of the present invention,
Only a portion of the photosensitive agent 33, for example, the center portion, is thicker. Therefore, the Bragg angle margin Δθ in the large film thickness part
(FIG. 6) can be made smaller than the other photosensitive agent parts.

FIG. 1 shows an embodiment of a method for producing such a hologram dry plate.

The characteristic of FIG. 1 is that the photosensitive agent is applied in two layers. That is, first, a first layer of photosensitive agent 33 is uniformly applied onto the substrate 31.

Next, a portion where the film thickness is desired to be thickened (the center portion in the illustrated embodiment) is covered with a mask 23, and the photosensitive agent JIi 33 is exposed by irradiating an incoherent light beam 22 from the incoherent light source 21. This state is shown in FIG. 1(A).

This exposure is a non-interference exposure. As a result, as shown in FIG. 2B, only the peripheral portion 33B of the hologram dry plate excluding the central portion corresponding to the mask 23 is exposed, and the central portion 33A remains unexposed. At this stage, no development processing is performed yet.

Next, the mask 23 is removed, and the second layer of photosensitizer 35 is uniformly applied on the first layer of photosensitizer 33 [FIG. 3(C)]
]. The photosensitive agent can be applied, for example, by a known spin code method.

Thereafter, as shown in FIG. 1(D), interference exposure is performed by irradiating two coherent light beams, for example, two laser beams of a peace wave 15 and a spherical wave 17, according to a normal hologram production method. At this time, the center part 33A of the first layer photosensitive agent 33
Since it is unexposed, it is subjected to interference exposure together with the second layer photosensitive material 35, but since the peripheral part 33B of the first layer has already been preliminarily exposed, it is not exposed any further. Clogged,
In the hologram dry plate, interference fringes are recorded only in the central part over a thickness of two layers, whereas in the peripheral part, interference fringes are recorded only in one layer corresponding to the thickness of the second Wj. Finally, by developing the hologram dry plate, the non-interference exposed area, that is, the pre-exposed area (peripheral area) of the first layer photosensitive material 33 becomes a transparent film 33B', and the entire surface of the second layer photosensitive material 35 and the first
A hologram 40 is formed in the center of the N photosensitive agent 33 [
Same figure (E)].

In this way, it is possible to equivalently create a hologram with a thick film only in the center.

Note that the preliminary exposure described above may use one of coherent light beams such as a laser beam. This is because interference fringes are not formed with a single coherent light beam.

FIG. 2 shows a second embodiment of the present invention, in which ultraviolet rays are used as the preliminary exposure light beam and the substrate 3 is
It is characterized by being incident from the first side.

In FIG. 2, a photosensitive agent 33 is formed on a transparent substrate 31, as in FIG. 1. A mask 23 is attached to a predetermined portion on the substrate 31, and the bottom surface of the substrate 31 is irradiated with ultraviolet light 26 from an ultraviolet light source 25. Since the ultraviolet rays are largely absorbed within the transparent substrate 31 and the photosensitive material 33, the ultraviolet rays proceed while attenuating as shown at 26' in FIG. 2(A), thereby exposing the photosensitive material 33 to non-interference light. Therefore, the substrate 31
By appropriately selecting the intensity or wavelength of the ultraviolet light m26 depending on the thickness of the photosensitive material 33, it is possible to completely absorb and eliminate the ultraviolet light in the middle of the photosensitive agent 33. If the photosensitive agent 33 is clogged, only the thickness portion of the photosensitive agent 33 closer to the substrate 31 (bottom portion in the illustrated embodiment) is exposed halfway. Blockage, 2nd
As shown in Figure (B), the surface side 33B of the photosensitive agent 33 is unexposed halfway. It goes without saying that the photosensitive agent portion 33A corresponding to the mask 23 also remains unexposed.

The hologram dry plate pre-exposed in this way is shown in Figure 2 (C).
Two or more laser beams as shown in 15.17
When interference exposure is performed by , only the unexposed portions 33A and 33B are subjected to interference exposure, and interference fringes are recorded. By developing this, the image shown in FIG. 2(D) is formed on the substrate 31.
As shown in FIG. 3, a hologram 33B' is equivalently formed in which only the central portion 33A' is a thick film.

FIG. 3 shows yet another embodiment of the invention.

The embodiment shown in FIG. 3 is characterized by the use of a Lippmann hologram. That is, as shown in FIG. 3A, a hologram dry plate having a transparent substrate 31 coated with a photosensitive agent 33 has a mask 23 on both sides corresponding to the area where the film should be thickened (in the illustrated embodiment, the center area). The laser 27 is irradiated from both sides.

As a result, as is well known, a plurality of interference fringes (Lippmann holograms) 37A are recorded on the photosensitive agent 33, except for the central portion 33A covered by the mask 23, approximately parallel to the recording surface, alternating with the unexposed layer 37B. Ru. Therefore, half of the film thickness of the peripheral portion of the photosensitive agent 33 (the portion not covered by the mask 23) has been exposed in advance.

Next, as shown in FIG. 3(B), after removing the mask 23, a laser beam 15. is applied to the hologram dry plate from one side.
17 to perform main exposure. As a result, a portion excluding interference fringes 37A (exposed portion) recorded parallel to the substrate surface during preliminary exposure, that is, a central portion 33A and an unexposed portion 37B.
desired interference fringes are recorded. By developing the hologram 38A in the third embodiment as well, the hologram 38A formed in the center becomes different from the hologram 38B formed in the periphery (corresponding to the unexposed layer 37B described above).
It will equivalently have twice the film thickness.

In the embodiment shown in FIG. 3, interference fringes (Lippmann holograms) are recorded even during preliminary exposure, so the preliminary exposure conditions must be designed so that the interference fringes are different from those during main exposure. is necessary.

〔effect〕

As described above, according to the present invention, it is possible to obtain a hologram dry plate in which a photosensitive agent having locally different film thicknesses is coated on a substrate, and it is possible to partially change hologram characteristics within the same plane as necessary. Its uses are extremely wide-ranging.

[Brief explanation of drawings]

Figures 1 (A) to (E) are illustrative views showing the first embodiment of the hologram production method according to the present invention in order of steps, and Figures 2 (A) to
(D) is an illustrative diagram showing the hologram production method according to the second embodiment of the present invention in the order of steps, FIGS. 3(A) and (B) are illustrative diagrams showing the third embodiment of the present invention, and FIG. A perspective view showing the basic structure of a hologram window to which the present invention can be applied, FIG. 5 is a cross-sectional view of the hologram window shown in FIG. 4, and FIG. 6 is a characteristic line of diffraction efficiency and transmittance of the hologram with respect to incident angle figure,
FIG. 7 is a diagram showing the relationship between the film thickness of the photosensitive material of the hologram and the Bragg angle margin. 15.17... Laser beam, 23... Mask, 31... Transparent substrate, 33... Photosensitive agent.

Claims (1)

[Claims] 1. A hologram dry plate coated with a photosensitive agent (33) on a transparent substrate (31) is exposed to a plurality of laser beams (15, 17).
2.) A method for producing a hologram, characterized in that, prior to performing interference exposure by irradiating a hologram, only a predetermined portion of a photosensitive agent is locally pre-exposed in advance. 2. The hologram production method according to claim 1, wherein the preliminary exposure is non-interference exposure performed by masking only a predetermined portion. 3. The method for producing a hologram according to claim 2, characterized in that after non-interference exposure, a second layer of photosensitizer is applied to the entire surface of the photosensitizer, and then this is subjected to interference exposure with a plurality of laser beams. . 4. The non-interference exposure is performed by masking only a predetermined portion of the transparent substrate and irradiating ultraviolet rays of a predetermined intensity from the substrate side.
The hologram creation method described in section. 5. The above-mentioned preliminary exposure is Lippmann hologram exposure in which a plurality of interference fringes substantially parallel to the substrate surface are recorded on the photosensitive agent by entering a laser beam from both sides of the dry plate. The hologram creation method described in section.