JP2518505B2 - Diffraction grating spectrometer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrometer using a holographic diffraction grating.

[0002]

2. Description of the Related Art A plane diffraction grating has conventionally been formed by mechanical cutting to form a grating groove, and the grating pattern is an evenly spaced linear grating.
This type of grating has no aberrations on its own,
In the case of a concave mirror used as a collimator element and a telemeter element like a Littrow mount spectroscope, a spherical mirror is used as the concave mirror and it is used in an off-axis state, so that aberration is generated by these concave mirrors. In order to correct this aberration, the grating pattern of the diffraction grating may be made special so that the aberration generated by the collimator mirror and the camera mirror is canceled by the diffraction grating. There is a possibility of producing a lattice pattern close to such a special lattice pattern. However, in conventional holographic diffraction gratings, spherical waves are used as the recording light for forming the diffraction grating pattern on the grating substrate, so the grating pattern is limited to the group of intersecting lines between the rotating hyperboloid group and the grating substrate. However, the aberration correction was insufficient. In a spectrograph using a concave diffraction grating such as the Seya / Namioka mount spectroscope, since the diffraction grating itself has an image forming action, a collimator element or a telemeter element is not necessary, and there is no aberration caused by these elements. Aberration appears in the image forming property of the grating. In this case as well, aberrations have come to be corrected by producing a grating pattern by using holography, but in this case as well, since spherical waves have been used for recording light in the past, it is sufficient. Aberration correction was not possible.

[0003]

SUMMARY OF THE INVENTION The present invention is intended to ensure that the above-mentioned aberration correction is complete in a diffraction grating spectroscope, especially a Seya-Namioka mount spectrograph and a Littrow mount spectrograph.

[0004]

The diffraction grating to be used is such that aberration of the spectroscope is corrected by causing aberration in the opposite direction to correct the aberration generated by the optical system of the spectroscope. In order to make the grating have the above-mentioned aberration characteristics, the diffraction grating is a holographic diffraction grating, and the light flux used in the exposure is an off-axis of the divergent light flux from the point light source and is reflected by a concave mirror. And

[0005]

In the spectroscope to which the present invention is applied, the collimator mirror and the camera mirror are used off-axis, so that an aberration occurs. In principle, however, such an aberration is an aberration opposite to that of the diffraction grating. It is expected that it can be corrected by generating Even if such a diffraction grating is made by a holographic method, the exposure conditions cannot be derived only from the principle described above. If you decide on the layout of each part of the spectroscope, the optimum layout for holographic exposure is required, but if you change the layout of the spectroscope, the optimum layout for exposure also changes. You need to figure out where. The invention shows the arrangement of the spectrograph and the holographic exposure so spotted.

[0006]

EXAMPLE This example relates to a Seya-Namioka mount spectrometer. The diffraction grating in this embodiment is a concave spherical surface having a radius of curvature of 500 mm and the grating pitch at the center is 60.
The number is 0 / mm, and a spectroscopic system using this is shown in FIG. 10 is the concave diffraction grating according to the present invention, 6 is an entrance slit, 7 is an exit slit, and the distance r from the entrance slit 6 to the grating center 0 is r = 409.8374 mm, and the distance r ′ from the grating center to the exit slit is r ′ = 410.8190
mm, the angular distance θ between the entrance slit and the exit slit with respect to the center of the grating is 69.7083 °, and the usable wavelength range is 10
It is 0 to 700 nm. FIG. 2 shows the arrangement of the diffraction grating 10 at the time of recording the grating pattern. Reference numeral 11 denotes a diffraction grating substrate, which is a concave spherical surface having a radius of curvature of 500 mm, and the normal line standing at the center 0 is N. In the plane containing N, the normal N and the angle α
= Distance from the 0 point in the direction away from 4.77 ° r = 199
The first point light source 12 is placed at a position of 9.4 mm, and with respect to the normal line N, the angle β = 11 ° is provided on the side opposite to the point light source 12, and 0
The center 0'of the concave spherical mirror 13 is placed at a position of distance r '= 871.4 mm from the point, and it is separated from the line connecting the 0'point and 0,0' by an angle 2r = 16.4 ° toward the normal line N, The second point light source 14 was arranged at a position P = 204.9 mm from 0 ′. Laser light having a wavelength of 457.93 nm was used as the recording light. In the present invention, the distance between each element
The value of the curvature equal length of the child is
The relative value used as the reference is sufficient. About the next example
Is also the same. FIG. 3 is a spot diagram (calculated value) when the above diffraction grating and a conventional holographic diffraction grating with coma aberration correction are used and compared in the spectroscope shown in FIG. 1 , and the present invention is excellent at each wavelength. I understand that.

This is an embodiment for a Littrow-mounted spectroscope and relates to a plane diffraction grating. FIG. 4 shows the above embodiment. 1 is a plane diffraction grating substrate, 2 and 3 are
Each of the first and second recording light source points is formed by dividing a laser beam emitted from the same laser (not shown) into two and converging the laser beams. The spherical waves diverging from the recording light source points 2 and 3 are reflected as aspherical waves by the first and second concave mirrors 4 and 5, respectively, and form interference fringes on the diffraction grating substrate 1. FIG. 5 shows an example of a Littrow mount spectroscopic system using a holographic plane diffraction grating prepared according to the present invention. The wavelength range of the spectroscopic system is 200-800n
m, the grating constant at the center of the diffraction grating 12 is 1/1800 m
m, and the collimator mirror 8 is a spherical mirror having a radius of curvature of a unit length. The details of the production of the diffraction grating will be described. A laser beam having a laser wavelength of 441.6 nm is used as a recording beam, and the exposure system is arranged as shown in FIG. 4 by pc = 0.3986 qc = 0.8710 tc = 6.188 ° pd. = 0.3912 qd = 0.8708 td = 13.545 °. Also, the curvature radii R4 and R5 of the concave mirrors 4 and 5 are R4.
= R5 = 1.000. The arrangement of the spectroscope is as shown in FIG. 5, r = 0.4988D = 0.40887, D '= 0.4.
093, r '= 0.4973, θ = 4.290 °, 2K
= 2.405 °, θ ′ = 5.709 °, use order −1,
The radius of curvature R8 of the collimator mirror 8 is R8 = 1.000. Therefore, the radii of curvature of qc, qd and the first and second concave mirrors 4, 5 are equal to or near the radius of curvature of the collimator mirror 8. In the above example, concave mirrors are used for the two recording light sources 2 and 3, respectively.
In many cases, it is sufficient for this configuration to employ at least one of the two recording light sources. Also for the diffraction grating substrate, besides the plane, a cylindrical surface,
It is possible to use a spherical surface or the like. Regarding the value of each parameter shown in each of the above-mentioned examples, the aberration characteristic is stable in the vicinity of the value, and the aberration characteristic hardly changes even if it is changed a little.

[0008]

As compared with the conventional holographic diffraction grating, the diffraction grating according to the present invention forms the grating pattern by using the aspherical wave for the recording light, so that the optical element or the diffraction grating constituting the spectroscope is formed. The correction of the aberration generated by using itself in the off-axis state is better than that of the conventional holographic diffraction grating. If a concave spherical mirror is used off-axis to obtain an aspherical wave, it is not necessary to use an aspherical optical system, and the grating pattern recording optical system of the diffraction grating can be adjusted very precisely to the parameters of the optimum design. Can be configured.

[Brief description of drawings]

FIG. 1 is a plan view of a spectroscope according to an embodiment of the present invention,

FIG. 2 is a plan view showing the arrangement of a grating pattern recorded next to the diffraction grating of the embodiment,

FIG. 3 is a graph showing the effect of the same embodiment,

FIG. 4 is a plan view showing an arrangement of a diffraction grating of another embodiment of the present invention during recording of a grating pattern,

FIG. 5 is a plan view of a spectroscope using a diffraction grating according to the example.

[Explanation of symbols]

 1 plane diffraction grating substrate 2,3 recording point light source 4,5 concave mirror 6 entrance slit 7 exit slit 8 collimator mirror 9 exit slit 10 concave diffraction grating 11 concave diffraction grating substrate 12 plane diffraction grating

Claims (2)

(57) [Claims] 1. In a Seya-Namioka mount spectrometer, a diffraction grating substrate having a concave spherical surface is used, and a point light source is arranged at an off-axis position with respect to a concave mirror having substantially the same radius of curvature as that of the diffraction grating substrate surface. Using a holographic concave diffraction grating made by forming an interference pattern on the, and setting this as a relative value of 500 with respect to the radius of curvature of this concave diffraction grating, the spectroscope measures from the entrance slit to the diffraction grating center. The distance r and the distance r ′ from the center of the diffraction grating to the exit slit are respectively about 410, the angle θ formed by the positions of both slits with respect to the center of the diffraction grating is about 69.7 °, and the exposure conditions of the holographic diffraction grating are as follows. A diffraction grating spectroscope characterized in that When this was used as a 500 on the basis of the curvature radius of the serial concave surface diffraction grating, r by a relative value: the distance of about 2.00 × 10 3 ^r between the diffraction grating substrate center and the first point light source ': the diffraction grating substrate center distance of about 871 p between the concave mirror centers: distance of about 205 between the concave center and the second point light source alpha: Zhang Ru angle about 4.77 ° relative to the grating substrate center normal line and the first point light source grating substrate center β: The angle between the normal to the center of the diffraction grating substrate and the center of the concave mirror is about 11 ° γ: The angle between the center of the diffraction grating substrate and the center of the second point light source is about 8 from the concave mirror 2 ° exposure wavelength 457.93nm 2. A Littrow mount spectroscope, wherein the diffraction grating used is a plane diffraction grating, and when the radius of curvature of the collimator mirror is taken as 1 and the spectroscopic parameters are D and D. ': Distance between the center of the diffraction grating and the collimator mirror about 0.41 θ: Angle between the center of the diffraction grating and the center of the collimator mirror about 4. 3 ° θ ': Angle formed by the center of the diffraction grating and the center of the exit slit with respect to the center of the collimator mirror . 7 ° K: The angle between the incident light and the reflected light at the center of the diffraction grating is about 1.2 ° , and the holographic exposure condition of the diffraction grating is pc, pd: the center of the diffraction grating substrate and the first and second Distance between concave mirrors : about 0.4 qc, qd: First point light source Distance between first concave mirror and second point light source Second distance between concave mirrors : about 0.87 τc: First point light source and center line of first concave mirror Is about 6.2 ° τd about the center of the concave mirror: The second point light source and the center line of the second concave mirror are about 13.5 ° about the center of the concave mirror and the exposure wavelength is 441.6 nm. Diffraction grating spectrometer