JPH0827403B2 - Diffraction grating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a diffraction grating manufactured by holography.

(B) Conventional technology In a spectroscope using a concave diffraction grating, aberration appears in the image forming property of the concave diffraction grating. To correct such aberration, holography is used to create a special pattern as the grating pattern of the concave diffraction grating. Is being implemented. However, in the past, spherical waves were used as the recording light for forming the grating pattern on the grating substrate, so the grating pattern is limited to the group of intersecting lines of the rotating hyperbola group and the grating substrate, and sufficient aberration correction is possible. There wasn't. In particular, in the case of photodrying or a spectroscope using an array detector, the aberration in the dispersion direction is corrected, the image plane is made closer to the plane, and the center of the image plane is substantially perpendicular to the diffraction grating center direction. Since it is necessary to correct the imaging characteristics to meet the requirement of
For example, although the effective efficiency is lowered due to astigmatism, the aberration is not corrected in this direction.

Further, the plane diffraction grating has conventionally been formed by mechanical cutting to form a grating groove, and the grating pattern is a linear grating with equal intervals. This type of diffraction grating has no aberration by itself, but collimator element and telemeter element In spectroscopes that use concave mirrors, the spherical mirrors are used as the concave mirrors and they are used off-axis, so aberrations are generated by these concave mirrors. In order to correct this aberration, the grating pattern of the plane diffraction grating may be made special so that the diffraction grating has an aberration that cancels the aberration generated by the collimator mirror and the camera mirror. Also, by using holography, such a special grid pattern is produced. However, aberration correction was inadequate because spherical waves were used as the recording light.

(C) Problems to be Solved by the Invention The present invention is intended to improve the formation of the grating pattern of the diffraction grating using holography to enable more complete aberration correction.

(D) Means for Solving the Problem The diffraction grating of the present invention is a holographically divergent light source point in the horizontal and vertical directions of the recording light for recording the diffraction grating pattern on the diffraction grating substrate. It is characterized in that the distance to the diffraction grating substrate is substantially changed.

(E) Action In the method of manufacturing a diffraction grating pattern by holography, two beams of light that can interfere with each other are projected onto the diffraction grating substrate to form a diffraction grating pattern, and this interference pattern is printed and recorded on the substrate surface. The two light fluxes are referred to as recording light, and the light source is referred to as recording light source. Conventionally, a plane wave region or a spherical wave is used as the above two recording lights. On the other hand, according to the present invention, since the distance from the divergent light source point in the horizontal and vertical directions of the diffraction grating to the diffraction grating substrate is substantially changed in the ray direction of the recording light, the light having different focal points in the horizontal and vertical directions ( The recording light is astigmatic light. As a result, the parameters of the recording conditions that form the interference pattern are increased, the obtained interference patterns are rich in variation, and the degree of freedom in selecting the interference pattern is increased. I can do it now.

When spherical waves are used, the only parameter that increases the parameters of the recording conditions is the data of the position of the point light source. However, when the astigmatic light is used, the position of the point light source in the horizontal and vertical directions is substantially the same. Since the parameters of the recording condition related to the vertical imaging condition are increased, the aberration of the entire optical system of the spectroscope, especially the astigmatism is effectively corrected. It will be possible.

(F) Example (when a spherical diffraction grating substrate is used) FIG. 2 is a diagram showing the arrangement of a conventional spherical diffraction grating during recording of a grating pattern, in which 4 is a holographic interference fringe recorded and diffracted. Spherical diffraction grating substrates 5, 6 coated with a photosensitizer for the grating are laser light source points for generating spherical waves.
In this case, stripes are generated on the line of intersection between the substrate and the rotating hyperbolic group whose focal points are the optical origins 5, 6. In this case, specific recording conditions are r _C = 0.9896, γ = −4.764 ° r _D = 0.9088, δ = 10.101 ° when using a laser beam having a wavelength of 441.6 nm.

FIG. 1 has the same horizontal (dispersion) direction focal line as the conventional diffraction grating shown in FIG. 2, and in order to correct astigmatism, the vertical focal line is almost at the center of the horizontal focal line. FIG. 6 is a diagram showing an arrangement when recording a grating pattern of the diffraction grating of the present invention that forms a grating pattern (see FIG. 3) of diffraction gratings that intersect with each other. Reference numeral 7 is a spherical diffraction grating substrate, 8 is a spherical mirror having a curvature radius of 0.6132, 9 is a toroidal mirror having a horizontal curvature radius of 0.6132 and a vertical curvature radius of 0.5852, and 10 and 11 are laser light source points for emitting spherical waves. The specific recording conditions in this case are: P _C = 1.5819, q _C = 0.5923, τ _C = 15.000 ° P _D = 1.5831, q _D = 0.5923, τ _D = 15,000 ° when using laser light with a laser wavelength of 441.6 nm Is. In the figure Are the focal points by the concave mirrors 8 and 9 of the laser light source points 10 and 11 in the horizontal and vertical directions, respectively, so that the recording by the astigmatic light, that is, the light source points in the horizontal and vertical directions of the diffraction grating in the beam direction of the recording light. The lattice pattern can be recorded by substantially changing the distance from the substrate to the lattice substrate.

An example of a spectroscopic system using the diffraction grating of the above embodiment is shown in FIG. 1 is an entrance slit, 2 is a diffraction grating according to the present invention, 3
Is the photographic plate or array detector surface, wavelength range 350nm ~ 7
It should be installed at a position where the deviation from the horizontal (dispersion) direction focal line is minimized at 50 nm. Arrangement of the spectroscopic system, r = 0.9514 In FIG. 3, alpha = 19.268 ° _{r '1 = 1.0035, β 1} = -7.164 ° _{r' 2} = 1.0104, a beta ₂ = 6.309 °, the horizontal direction of the diffraction grating 2 Has a radius of curvature of 1.000.

(When Toroidal Diffraction Grating Substrate is Used) FIG. 4 is a diagram showing the arrangement of a diffraction grating of another embodiment of the present invention used in the same spectroscopic system of FIG. It has a horizontal focal line and a vertical focal line on the horizontal focal line of the conventional diffraction grating shown in FIG. 2 (see FIG. 3), and astigmatism is corrected over the entire wavelength range. In the figure, 12 is a toroidal plane diffraction grating substrate, 1
3 is a spherical mirror having a radius of curvature of 1.000, and 14 and 15 are laser light source points which emit spherical waves having a wavelength of 441.6 nm. The specific recording conditions are P _C = 1.9854, q _C = 0.9957, τ _C = 5.288 ° r _D = 0.9908, γ = -4.764 °, δ = 10.134 °. In the figure Are the focal points in the horizontal and vertical directions by the laser light source point 14, respectively, and this enables recording by the astigmatic light, that is, the distance from the light source point in the horizontal and vertical directions of the diffraction grating to the grating substrate in the ray direction of the recording light. It is possible to record a grid pattern by substantially changing

(When a Planar Diffraction Grating Substrate is Used) FIG. 5 is a diagram showing an arrangement of a diffraction grating of still another embodiment of the present invention when recording a grating pattern. 24 is a plane diffraction grating substrate, 20 and 22 are recording light source points, 21 is a spherical mirror with a radius of curvature of 1.0000, 23 is a horizontal radius of curvature 1.0000, a vertical radius of curvature.
It is a 0.9388 toroidal mirror. The specific recording conditions in this case are: p _C = 1.9724, q _C = 0.9767, τ _C = 5.121 ° p _D = 2.0799, q _D = 0.9879, τ _D = 4.956 ° when using laser light with a laser wavelength of 441.6 nm γ = 33.438 ° δ = 1.210 °. In the figure Are the focal points in the horizontal and vertical directions by the concave mirrors 21 and 23 of the laser light source points 20 and 22, respectively. From this, recording by stigmatic light, that is, the light source points in the horizontal and vertical directions of the diffraction grating in the beam direction of the recording light The lattice pattern can be recorded by substantially changing the distance from the substrate to the lattice substrate.

FIG. 6 is a view showing an example of a spectroscopic system using the diffraction grating of the above embodiment, in which 16 is an entrance slit, 17 is a concave mirror, 18 is a diffraction grating according to the present invention, and 19 is an exit slit. Diffraction grating 18
Is installed at the position where the deviation from the horizontal (dispersion) direction focus is minimized in the wavelength range of 300 to 900 nm. When the concave mirror 17 is a spherical mirror having a radius of curvature of 1.000 and the diffraction grating 18 is a grating constant of 1/1200 mm and the order of use is minus the first order in the figure, r = 0.7755, D = 0.6204, r '= 0.7064 θ = 10 °, 2K = 20 °.

In the above embodiment, two recording lights and an astigmatic light are used, but of the two recording lights in terms of design,
Astigmatic light for at least one,
That is, it is often sufficient to change the distance from the light source point to the grid substrate.

(G) Effect The diffraction grating according to the present invention uses astigmatic light as the recording light as compared with the conventional holographic diffraction grating, and from the light source points in the horizontal and vertical directions of the diffraction grating in the recording beam direction to the grating substrate. Since the grating pattern is formed by substantially changing the distance of, the correction of the aberration generated by the spectroscope (diffraction grating) becomes better than that of the conventional holographic diffraction grating. In particular, it has a remarkable effect on the correction of astigmatism. FIG. 7 is a diagram showing this effect. The radius of curvature of the concave diffraction grating in the horizontal direction is 200 mm, and monochromatic light having several wavelengths on the dry plate surface 3 shown in FIG. 3 is emitted from the center of the entrance slit 1. It shows the spread due to aberration when incident.

The area of the diffraction grating was 40 × 40 mm ² . (A) is a case where the conventional diffraction grating (FIG. 2) is used, (b) is a case where the diffraction grating of the embodiment of the present invention shown in FIG. 1 is used,
FIG. 6C shows the case where the diffraction grating of another embodiment of the present invention shown in FIG. 4 is used. Aberrations in the vertical direction in the figures (b) and (c) according to the present invention as compared with the figure (a). That is, it is recognized that the astigmatism is significantly corrected.

[Brief description of drawings]

FIG. 1 is a plan view showing the arrangement of a diffraction grating according to the present invention during recording of a grating pattern, FIG. 2 is a plan view showing the arrangement of a conventional diffraction grating during recording of a grating pattern, and FIG. FIG. 4 is a plan view of a spectroscope using the diffraction grating of the embodiment of FIG. 4, FIG. 4 is a plan view showing the arrangement of another diffraction grating according to the present invention when recording a grating pattern, and FIG. FIG. 6 is a plan view showing the arrangement of the diffraction grating when recording the grating pattern.
FIG. 5 is a plan view of a spectroscope using the diffraction grating of FIG.
FIG. 7 is a graph showing the performance and effect of the diffraction grating according to the present invention. 1,16 …… Inlet slit, 2,18 …… Diffraction grating 3 …… Dry plate (detector) surface 4,7,12,24 …… Diffraction grating substrate 5,6,10,11,14,15,20, 22 …… Recording light source point 8,23 …… Toroidal mirror, 9,13,21 …… Spherical mirror 17 …… Concave mirror, 19 …… Exit slit

Claims (1)

[Claims] 1. A diffraction grating having a grating pattern manufactured by projecting two interfering light beams on a diffraction grating substrate surface to form an interference pattern and recording the interference pattern on the substrate surface. A diffraction grating characterized in that the distance from the divergent light source point in the horizontal and vertical directions of the diffraction grating to the diffraction grating substrate is substantially changed in the direction of the principal ray of the light flux.