JPH06194510A - Diffraction grating spectrsocope - Google Patents

Abstract

PURPOSE:To well correct aberrations by using luminous fluxes which are obtd. by reflecting divergent luminous fluxes from spot light sources with a off axial concave surface mirrors by using a holographic diffraction grating in exposing and contains the aberrations. CONSTITUTION:The radius of curvature of the concave surface diffraction grating 10 of the Seya-Namioka mounting spectroscope is set at 500, the distance r from an incident slit 6 to the center of the diffraction grating and the distance r' from the center of the diffraction grating to an exit slit 7 are respectively set at 140 and an angle theta to be formed by both slit positions with the center of the diffraction grating is set at about 69.7 deg.. The exposing conditions of the holographic diffraction grating are set as follows: The spot light source 14 is disposed at a point of the distance r= about 2.00X10<3> from the point 0 in the direction apart an angle alpha= about 4.77 deg. from a normal N erected at the center 0 of a diffraction grating substrate 11 (concave spherical surface of 500 radius of curvature). The spot light source 14 is disposed in a position of the distance p= about 205 from 0' apart an angle 2r= about 16.44o from a line connecting the centers 0', 0, 0' of the concave spherical surface mirror 13 in a position of r'= about 871 apart an angle beta= about 11 deg. on the opposite side. The exposing wavelength is set at 457.93nm.

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 imaging 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 point light source 12 is placed at a position of 9.4 mm, and with respect to the normal line N, the point β is separated by an angle β = 11 ° on the side opposite to the point light source 12, and the concave spherical mirror 13 is placed at a position r ′ = 871.4 mm from the 0 point. The center 0 ′ is placed, and the point light source 14 is arranged at a position p = 204.9 mm from 0 ′, which is separated from the line connecting the 0 ′ and 0,0 ′ by the angle 2r = 16.4 ° toward the normal line N. did. Laser light having a wavelength of 457.93 nm was used as the recording light. The third is a spot diagram (calculated value) when the above diffraction grating and a conventional holographic diffraction grating corrected for coma are used and compared in the spectroscope shown in FIG. 3, and the present invention is excellent at each wavelength. I know that

This is an embodiment for a Littrow-mounted spectroscope and relates to a plane diffraction grating. FIG. 4 shows the above embodiment. Reference numeral 1 is a plane diffraction grating substrate, 2 and 3 are recording light source points, each of which is formed by dividing a laser beam emitted from the same laser (not shown) into two and converging the laser beam. The spherical waves diverging from the recording light source points 2 and 3 are reflected as aspherical waves by the 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 to 800 nm, the grating constant at the center of the diffraction grating 12 is 1/1800 mm, and the collimator mirror 8 is a spherical mirror having a unit radius of curvature. The details of the production of the diffraction grating will be described. As the recording light, the laser wavelength is 441.6 nm.
4, the exposure system is arranged as follows: 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, qc and qd, and the radius of curvature of the concave mirrors 4 and 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. However, 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, it is possible to use a cylindrical surface, a spherical surface, or the like in addition to the flat surface. Regarding the value of each parameter shown in each of the above-described 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)

[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. When a holographic concave diffraction grating made by forming an interference pattern is used and the radius of curvature of this concave diffraction grating is taken as 500, the distance r from the entrance slit to the center of the diffraction grating in the spectroscope is
The distance r ′ from the center of the diffraction grating to the exit slit is about 410, and the angle θ formed by the positions of both slits with respect to the center of the diffraction grating is about 69.7 °. The exposure conditions of the holographic diffraction grating are as follows. A diffraction grating spectroscope characterized in that When the radius of curvature of the concave diffraction grating is taken as a reference for each parameter defined by FIG. 2 and is set to 500, r about 2.00 × 10 ³ r about 871 p about 205 α about 4.77 ° β about 11 ° r about 8.2 ° exposure wavelength 457.93 nm 2. A Littrow mount spectrograph, wherein the diffraction grating used is a plane diffraction grating, and when this is set to 1 on the basis of the radius of curvature of the collimator mirror, the spectroscope defined by FIG. Is about 0.41 r, r ′ is about 0.5 ° θ is about 4.3 ° θ ′ is about 5.7 ° K is about 1.2 °, and the holographic exposure condition of the diffraction grating is But,
For the parameters defined by FIG. 4, pc, pd about 0.4 qc, qd about 0.87 tc, qd about 6.2 ° td about 13.5 ° exposure wavelength 441.6 nm Grating spectrometer