JPH0445831B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for producing a two-layer phase type hologram having a black angle suitable for scanning.

Background of the technology Phase-type holograms are made by projecting coherent light onto a photosensitive material layer from two directions, exposing the resulting interference fringes, developing them, and bleaching the resulting black and white fringes to make them transparent, but with a refractive index similar to that of the black and white fringes. It has become something that changes depending on the situation. The general properties of transmission and refraction will be explained with reference to Figure 1. In the figure, 10 is a phase type hologram, 11 is a pattern of interference fringes (in this case, the refractive index changing part) in the longitudinal section of the hologram, and 14 is a The pattern on the same surface is shown. 12 is reproduction light, 1
3 is diffracted light. Reproduction light 12 with wavelength λ is on surface 11
If the pitch of the surface 11 is _d , then the angle θ _d of the diffracted light 13 with respect to the surface 11 has the following relationship.

sinθ _d =λ/d±sinθ _i (1) When θ _d =θ _i (Plug condition), the intensity of the diffracted light 13 is the highest. In other words, this hologram is surface 11
is perpendicular, but this is due to the same angle (θ _i ) from the left and right with respect to the normal line set at the point of incidence, as described later.
θ _i = θ _d means that one of the hologram creation lights is reproduced, and the diffracted light at this time has the highest intensity. It is. If θ _i and θ _d are not equal, such a relationship will not hold and the intensity of the diffracted light will be low. For example, the reproduction light 12 is transmitted to the surface 10 of the hologram 10.
When incident perpendicularly to a (θ _i =0), the intensity of the refracted light 13 decreases considerably and the angle θ _d increases. Although it is desirable that the reproduction light 12 has the same angle of incidence as one of the creation lights, this may not be possible in some cases. For example, hologram scanner.
Scanners that rotate phase-type holograms and scan in a straight line are used for things such as reading barcodes.
For reasons explained later, the light beam needs to be incident on the hologram almost perpendicularly, and if the angle of incidence deviates, the desired linear scan cannot be obtained.

As shown in Figure 2, the principle of the hologram scanner is to move a phase-type hologram 10' whose pitch on the surface 11 is coarse and dense, and change the angle θ _d of the diffracted light 13 while keeping the incident light 12 stationary. That is what it is. The angle θ _d increases as the pitch d of the surface 11 becomes narrower, so when the incident light 12 is irradiated onto the hologram 10', which has dense edges and a rough center, and swings left and right, the diffracted light 13 becomes Scanning is performed in a fan shape between 13' and 13''. In a practical example, the hologram is a disk, multiple holograms with the same pattern are formed along the circumference, and scanning is performed repeatedly by rotating the disk. .In such a hologram scanner, the incident light 12 is incident perpendicularly, and the diffracted light 1
In order to keep the intensity of the interference pattern 3 always high, it is preferable that the longitudinal section 11 of the interference fringes be inclined. However, there is a problem in that this inclination angle is determined by the surface pattern 14, and the surface pattern 14 is determined by the desired scanning conditions (such as linear scanning by rotating the disk). This will be explained with reference to FIG.

Conventional technology and problems Figure 3 shows the conventional method for creating a phase-type hologram.
This is an example of silver salt bleach. First, as shown in a, a silver salt-based hologram photosensitizer 1 is coated on a glass substrate 2, and two coherent beams (for example, two beams with the same light source), one of which is an information beam and the other is a reference beam, are coated on a glass substrate 2. 2 laser beams) 3 and 4 are irradiated. Next, this substrate is developed and fixed to form black and white light and dark stripes in the layer 1' as shown in b (this is an amplitude hologram). When this is then bleached, the silver becomes transparent and has a high refractive index, changing to silver chloride, and a stripe (vertical section) 11 showing a change in refractive index as shown in c is formed in the layer 1''.This is a phase hologram. When a phase type hologram is irradiated with reproduction light 5, transmitted light (0th order light) 6 and ±1st order diffracted light 7, 8 are generated.The hologram scanner uses diffracted light 7 or 8, but the amount of these lights is It is desirable that the intensity is not significantly smaller than that of the incident light 5. However, if the reproduced light 5 has a different wavefront from the created lights 3 and 4 as shown in FIG. 3c, there is a problem that the intensity of the diffracted light 7 is small.
Generally, in a hologram scanner, the created wave and the reproduced wave are often different, so it is necessary to make sure that they are different enough to obtain sufficiently strong diffraction.

The above-mentioned rotating plate type linear scanning hologram scanner is made by making a spherical wave and a convergent spherical wave incident at equal angles, and the reproduction light is incident perpendicularly. Therefore, the incident angles of the created wave and the reproduced wave are different. In such a case, as shown in FIG. 4, using the hologram 10 created in the manner shown in FIG.
By tilting the beam, strong diffracted light can be obtained even if the reproduced wave is different from the created wave. The inclination angle of the longitudinal section 21 of the interference fringe obtained by this hologram copying method is along the midline 22 between the transmitted light 6 of the reproduction light 5 and the diffracted light 7. The interference fringes of the copied porogram 20 differ only in the slope of the longitudinal section 21 from that of the longitudinal section 11 on the master side, and the plane pattern is the same as that of the hologram 1.
As long as the values between 0 and 20 are in close contact, there will be no change. Therefore, if this phase type hologram 20 is used as a scanner, it is possible to make the light 12 perpendicularly incident on the surface and perform linear scanning with the highly intense diffracted light 13.

However, during this copying, it is necessary to maintain good adhesion between the holograms 10 and 20. If there is a minute gap, the pattern will become unclear and the diffraction efficiency will decrease. The disadvantage is that stripes) are formed.

OBJECTS OF THE INVENTION The present invention provides a phase-type hologram with a two-layer structure so that the Bragg angle during reproduction can be arbitrarily set.

Structure of the Invention In the method for producing a two-layer phase hologram of the present invention, two holograms stacked one above the other are both phase holograms, and the upper layer phase hologram is a lower layer hologram having a lower diffraction efficiency. A holographic photosensitive agent is applied directly onto the surface, and the holographic photosensitive agent is exposed through the lower layer hologram, developed and fixed, and the photosensitive agent is converted into a phase-type hologram with a different black angle than the lower layer hologram and a high diffraction efficiency. This will be described in detail below with reference to the illustrated embodiments.

Embodiments of the Invention FIG. 5 is a schematic explanatory diagram of the method of the present invention. First, as shown in a, a phase type hologram (efficiency 5 to 10%) 1'' with a black angle θ ₁ and a low diffraction efficiency is placed on a glass substrate 2.
are formed in the same manner as in FIG. 3 so that interference fringes form a desired pattern. If the exposure is sufficient, a pattern with strong contrast will be obtained and the diffracted light will be strong, and if the exposure is insufficient, the opposite will occur, so one way to create a low-efficiency hologram is to adjust the exposure. Next, this hologram 1″
is used as a base and another hologram photosensitive agent 7 is formed on the upper layer.
Apply. Thereafter, appropriate light 30 is irradiated from the glass substrate 2 side to expose the photosensitive agent 7. At this time, the photosensitive agent 7
A longitudinal cross section of interference fringes is formed along. Due to post-exposure processing, the Bragg angle θ ₂ (≠θ ₁ ) is changed as shown in b.
A phase type hologram 7' is formed. Since the cross-sectional view 41 of this hologram 7' is different from the vertical cross-section 11 of the basic hologram 1'', if the efficiency of the hologram 7' is increased, the existence of the basic hologram 1'' can be substantially ignored, and the black angle as a whole is It functions as a θ ₂ phase type hologram. c indicates this state. That is, if the reproduction light 34 is incident at the same angle θ ₂ as the creation light 30, the Bragg condition is satisfied and the diffracted light 35 reaches its maximum intensity. 36 is transmitted light.

In the case of the phase type hologram with the above-mentioned two-layer structure, (1) layers 1'' and 7 are in close contact with each other by coating, so the above-mentioned image blurring and copy stripes do not occur.Also, (2) the selection of photosensitive agent 7 By doing this, the intensity of the diffracted light 31 and the transmitted light 32 during exposure can be made equal, so that the interference fringes 41 of the hologram 7' can be clearly formed.Therefore, if this phase type hologram is used as a scanner, the vertical A laser beam, etc., incident at an angle close to , can be easily scanned in a straight line (as diffracted light 35).Also, when used as a master for hologram copying (10 in Fig. 4), the intensity of diffracted light 35 can be sufficiently increased. Next, detailed examples will be described.

A phase type hologram 1'', which is a basic hologram, is created by the following procedure.

A glass substrate 2 coated with a photosensitive agent PVC _Z to a thickness of 1 to 2 μm is used as a dry plate, and exposed with two beams of _Ar laser (incident angle ±15°, intersecting angle 30°). Develop and fix this to obtain a black angle θ ₁ = ±15°, efficiency 5 to 10.
% phase type hologram 1' is obtained. On top of this basic hologram 1″, PVC _Z is added as a photosensitive agent 7.
Apply 4 to 5 μm of Then, an A _r laser (corresponding to light 30) is irradiated from the basic hologram 1'' side at an incident angle of 30° to expose the PVC _Z layer 7. When this is developed and fixed, the PVC _Z layer 7 has a black angle θ ₂ =
30°, it is converted into a phase type hologram 7' with an efficiency of about 70%. In this state, the lower PVC _Z layer, that is, the basic hologram 1'' is substantially ignored due to its low efficiency, and a phase type hologram with a two-layer structure is obtained as a whole.

Effects of the Invention As described above, according to the present invention, the black angle of the phase type hologram can be changed to an arbitrary value different from that during recording, and the hologram black angle can be matched to the reproduction light, which is extremely useful. There are advantages.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a phase type hologram, Figure 2 is an explanatory diagram of a hologram scanner, Figure 3 is an explanatory diagram showing a conventional method for creating a phase type hologram, Figure 4 is an explanatory diagram of a hologram copy, and Figure 4 is an explanatory diagram of a hologram copy. FIG. 5 is a schematic explanatory diagram of the method of the present invention. In the figure, 1'' is a basic hologram, 7 is a hologram photosensitizer, and 7' is a phase type hologram.

Claims (1)

[Claims] 1. The two holograms stacked one above the other are both phase type holograms, and the upper layer phase type hologram is coated with a hologram photosensitizer directly on the surface of the lower layer hologram with low diffraction efficiency, and is exposed through the lower layer hologram. 2, characterized in that the holographic photosensitive agent is exposed, developed, and fixed to convert the photosensitive agent into a phase-type hologram having a Bragg angle different from that of the lower layer hologram and having high diffraction efficiency.
How to create a phase-type hologram with a layered structure.