JPS6368874A - Hologram exposure device - Google Patents

Abstract

PURPOSE:To adjust two pieces of luminous flux to equal optical path length by providing a liquid cylinder which transmits laser light on the optical path of at least one of the two pieces of luminous flux. CONSTITUTION:When the two pieces of luminous flux are not equal in optical path length, the liquid cylinder 20 is placed on the optical path of one of the two pieces of luminous flux which are split by a beam splitter 2 and shorter in optical path length, i.e. at a position 32 or 34. When liquid cylinders are arranged on the optical paths, this is not required. Here, how much the optical path length needs to be increased to equalize the two pieces of luminous flux in optical path length is predicted from the distribution of diffraction efficiency to nm order, so how long distance S is in concrete is calculated from the refractive indexes of the liquid in the cylinder and transparent windows 22 and 26, and a piston 24 is moved by a specific quantity in a specific direction based upon the calculation result to perform exposure again, thereby confirming the coincidence. Consequently, the two pieces of luminous flux are equalized in optical path length almost by single-time adjustment.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a hologram exposure apparatus, and more particularly to a hologram exposure apparatus that can be applied to a means for producing a hologram for a scanner in a laser printer or the like.

(Prior Art) An apparatus is known in which a laser beam from the same light source is split by a beam splitter, and the two beams thus obtained are guided onto a photosensitive material to expose hologram interference fringes. In this apparatus, most of the positive type photoresists 1 to 1 which are generally used as photosensitive materials have the property of being sensitive to visible light and to the short wavelength side of the blue region. Also, in this device,
When the coherence length of the laser beam determined by the light source is short, there is a restriction that the difference in optical path length between the two beams must be adjusted to within a trivial distance.

Ar laser (45
79A) has a long coherence distance on the short wavelength side, so
Although it has the advantage of having a large tolerance when adjusting the difference in optical path length to within the coherence distance, it has problems such as being expensive and having undesirable sensitivity matching with the positive type photo resist due to the novolak resin.

Therefore, the blue region 441 does not have the above problems, that is, it is inexpensive and compatible with the sensitivity characteristics of positive photoresists.
A He-Cd laser with a wavelength of 6A is used, but currently the coherence length is short, only 20 mm, and therefore the optical system arrangement accuracy cannot be improved by keeping the optical path length difference between the two beams within about 5 mm. This results in a distribution in the diffraction efficiency of the hologram diffraction grating. However, it is extremely difficult to assemble and adjust the optical path lengths of the two beams to be exactly equal.

(Objective) Therefore, the object of the present invention is to provide an improved hologram exposure apparatus using a laser with a short coherence length, which is equipped with a means for easily adjusting the optical path lengths of two light beams to be substantially equal. An object of the present invention is to provide a hologram exposure device.

(Structure) In order to achieve the second object, the present invention is characterized in that a liquid cylinder that can transmit laser light is provided on at least one optical path of two light beams. Hereinafter, a detailed explanation will be given based on one embodiment of the present invention.

In FIG. 3 showing an example of a hologram exposure apparatus suitable for implementing the present invention, reference numeral 1 indicates a laser light source, and in this example, a He--Cd laser is used.

The laser light emitted from the laser light source 1 passes through the mirror M1
The direction of the light beam is changed at the reflection point E, and the beam proceeds to the beam splitter 2, where it is split into two beams at the splitting point. One of the light beams related to the above division is reflected at the reflection point B by the mirror M2, and then passes through the objective lens L1, the pinhole of the pinhole plate 4, the collimator lens L2, and the hole of the mask plate 8 in order, and then passes through the hologram which is a photosensitive material. Disk 10 is reached.

In addition, the other light beams related to the division are reflected at the reflection point C by the mirror M3.
After being reflected by the objective lens L3, the pinhole plate 12
, the collimator lens L4, and the hole in the mask plate 8 as described above to reach the hologram 10.

In such a configuration, in order to form hologram interference fringes on the hologram disk 10, it is necessary to adjust the optical path lengths of the two beams, that is, the difference between them, to within 5Iw1.

As this adjustment means, for example, mirrors M1, M2, M3
There is a method to change the inclination of the beam splitter 2, but since these mirrors have a certain thickness, the center of rotation 0-0 and the reflecting surface MO do not necessarily coincide as shown in FIG. It is difficult to predict the amount of shift change in the reflected light beam with respect to changes in the rotation angle. This point proves to be even more difficult when considering that in order to create a diffraction grating with a specific spatial frequency, the incident angles of the two beams must be precisely matched.

In reality, a small jig or the like is used to adjust the inclination of a mirror, etc. so that the difference in length between the two beams falls within the coherence distance on the optical axis, and then a beam expander using an objective lens is used to direct the beam. It can be placed on the road, but if it is installed, the difference in length between the two light beams will be slightly distorted. This causes a distribution in the diffraction grating.

In order to correct this, the inclinations of mirror M2 and mirror M3 must be readjusted, and as a result, the hologram disk 1
Since the angle of incidence on 0 is distorted, it is necessary to further change the inclination of the mirror. As a result, the optical path length is also slightly affected, so in the end, the LJ must be adjusted several times to get closer to the desired state.

Such complicated operations can be solved by arranging the liquid cylinder 20 as shown in FIG. 1 at the position shown by the two-dot chain line on both of the two light beams shown in FIG. 3 or on some optical path. be able to.

In other words, if the angle of incidence of the two light beams on the hologram disk 1o is accurately matched by adjusting the inclination of a mirror, etc., the liquid cylinder 20 can be placed in the light beam with the shorter optical path length among the two light beams. be. Alternatively, liquid cylinders may be placed in advance in both optical paths.

As shown in FIG. 1, a transparent window 22 is held at one end of a main body 21 constituting a hydraulic cylinder 20.
The piston 24 housed in the screw head 24 is also provided with a transparent window 26, and the center portion of the other end of the screw 1 hem 24 is hollow to allow the light beam to pass therethrough. A bolt 28 is installed in the piston 24 to the port 1, and this bolt is attached to the main body 2.
1 and is fastened with a nut 29 at the penetrating portion.

Therefore, by turning the nut in one direction, the piston 24 can be slightly moved in the direction of increasing the cylinder internal volume. Bis I
To move the bolt 24 in the opposite direction, rotate the nut 29 in the opposite direction while pressing the bolt 28.

The cylinder is filled with water, oil, or any other suitable liquid that can transmit light of wavelengths within the trusted color range. In order to prevent excess or deficiency of liquid in the cylinder due to the reciprocating movement of the piston 24, a liquid reservoir 30 is provided upright from the main body 21 to store the liquid.

Further, each transparent window 22, 26 is coated with a single-layer or multi-layer antireflection film F depending on the refractive index on both sides in order to prevent reflected light from occurring at the boundary between the liquid and the air.

The reason why it is possible to substantially adjust the optical path length by intervening the liquid cylinder 20 described in 2 on the optical path is because in a liquid medium, the speed of light decreases to 1/n, where n is the refractive index of the liquid. be. For example, in FIG.
If the distance between 6 and 6 is S, then the actual optical path length in the liquid at this distance S corresponds to approximately S×n.

More specifically, the phenomenon of increase in the substantial optical path length similar to that in the liquid occurs in each transparent window 22, 26, but this phenomenon is so small that it can be ignored.

When implementing the present invention, for example, the following procedure is followed. First, when assembling the optical system shown in FIG. 3, a certain reference piston position is determined, the corresponding substantial optical path length SXn is determined, and the optical system is set taking this into consideration. Subtle differences between the two light beams caused by mismatch between the rotation axis of the mirror holder and the reflecting surface (see Fig. 2) are adjusted by changing the position of the piston of the liquid cylinder.

In the above, confirmation of whether the optical path lengths of the two light beams match is specifically performed as follows. First, as shown enlarged in FIG. 4, the photoresist 32 is
A diffraction grating is exposed on the top and the diffraction efficiency distribution is examined using an appropriate observation means.

Then, when the optical path lengths of the two light beams are the same, the optical path lengths at the center become equal, and the diffraction efficiency distribution also becomes high at the center, as shown in FIG. Therefore, when the diffraction efficiency distribution is as shown in FIG. 6, there is no need for adjustment.

Unlike the above, if the optical path lengths of the two beams do not match, the fifth
As shown in the figure, the diffraction efficiency distribution is on the upper right or upper left.

In such a case, adjust as follows. The liquid cylinder 20 shown in FIG. 1 is connected to the beam splitter shown in FIG.
It is placed at the position indicated by 32 or 34 on the optical path of the two light beams divided by 2, which is thought to have a shorter optical path length. As described above, if liquid cylinders are arranged on each optical path in advance, this is not necessary. Here, from the above-mentioned diffraction efficiency distribution (see Figure 6), it can be predicted in the order of nm how much the optical path length should be increased to make the optical path lengths of the two beams equal.
From the refractive index of 2.26, it is calculated what value the distance S should specifically be.

Therefore, the piston 24 is moved by a predetermined amount and in a predetermined direction based on this calculation result. Then, expose again and check.

With the method described above, the optical path lengths of the two light beams can be made to substantially match with almost one adjustment. As mentioned above, the optical path length can be adjusted in principle by parallel movement of the mirrors that constitute the optical system, but in this case, the angle of incidence also changes. On the other hand, when adjusting the effective optical path length on the way without moving the mirror as in this example, the mirror holders do not need to be as precise, and the operation to equalize the optical path length is not necessary. It has the advantage of being extremely easy.

However, in order to increase the accuracy of adjustment, a transparent window 22.26
A precise parallel state must be maintained between them.

Further, by using a liquid cylinder that allows a large distance between the transparent windows 22 and 26, the degree of freedom in arranging the optical system can be increased.

(Effects) According to the present invention, the substantial optical path of two light beams can be quickly established with a simple operation, which is advantageous.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a liquid cylinder according to the present invention, FIG. 2 is a perspective view of a mirror and mirror boulder constituting an optical system, and FIG. 3 is an overall configuration diagram of a bologram exposure apparatus suitable for carrying out the present invention. FIG. 4 is a diagram explaining the state of incident light on the photoresist, and FIGS. 5 and 6 are diffraction efficiency distribution diagrams, respectively. 20...Liquid cylinder.

Claims (1)

[Claims] In a hologram exposure device that uses a laser with a short coherence length to expose interference fringes on a photosensitive material by two-beam interference, at least one of the cylinders has a liquid cylinder that can transmit the laser beam as a means for adjusting the optical path length of the two light beams. A hologram exposure device characterized in that it is provided on an optical path of.