JP2510191B2 - Concave grating spectrometer - Google Patents

Description

Detailed Description of the Invention a. TECHNICAL FIELD The present invention relates to a double monochromator using two concave diffraction gratings.

B. Conventional technology Problems to be Solved by the Invention When designing a double monochromator using two concave diffraction gratings, conventionally, two separate spectroscopes using one concave diffraction grating are designed and Was connected. However, in the conventional method, it is difficult for the image formation position obtained by the second diffraction grating to be constant, so that there is a problem that the resolution is reduced and the amount of monochromatic light having a desired wavelength is reduced.

FIG. 3 is for explaining the problems of the above-mentioned conventional double monochromator, in which light enters through the entrance slit 1a, the first diffraction grating 2a, the intermediate slit 3a,
(The first spectroscope up to here, the second spectroscope from here), the second
On the way to the diffraction grating 4a and the exit slit 5a, when the light is dispersed by the first diffraction grating 2a and the wavelength or the monochromatic light shown by the solid line has the image plane just on the intermediate slit 3a,
Light of other wavelengths (shown here by dotted lines) is in the middle slit
No image is formed on 3a.

Therefore, defocusing or aberration occurs at this point, resulting in a loss of light quantity. If the width of the intermediate slit is widened in order to avoid this, the resolution is lowered and the problem is not solved.
Also, when the first and second diffraction gratings have exactly the same design and are used depending on the same diffraction, the second one is the first.
Since the same defocus as that of No. 1 is produced, the amount of light and the resolution are further reduced in the image formation at the exit slit.

D. Means for problem solving. Function In the present invention, in a double monochromator type concave diffraction grating spectrometer using two concave diffraction gratings as the first and second diffraction gratings, the first and second diffraction gratings are formed by aspherical wave holographic exposure. At the same time, the above-mentioned problem is solved by designing the diffraction lines of the two diffraction gratings so as to correct the defocus of each wavelength based on the rotational scanning of the first diffraction grating. As can be seen from the above description, the present invention has the property that it can be specifically designed after the parameters of the first diffraction grating are given. Therefore, the action of the invention is as follows. Will be revealed.

F. EXAMPLE FIG. 1 shows a double monochromator of the present invention. The light enters from the entrance slit 1 to the first diffraction grating 2, the intermediate slit 3, the first spectroscope up to this point (the second spectroscope up to this point), the second diffraction grating 4, and the exit switch 5 in the first path. In the light split by the diffraction grating 2, when the image plane formed by the first diffraction grating 2 is on the intermediate slit 3 at the wavelength shown by the solid line, the image formation planes by other wavelengths shown by the dotted lines are on the intermediate slit. Theoretically, it is the same as before, but in this example, the arrangement of the first and second diffraction gratings (this includes parameters such as the entrance and exit distances and declination angles), By adjusting the ruled lines of the two diffraction gratings, the second diffraction grating forms an image substantially without focus dispersion at the exit slit. In this case, the width of the intermediate slit is
The size is set so that the diffracted light from the first diffraction grating does not hit the slit. Due to this, the loss of the light quantity due to the intermediate slit is eliminated, and the resolution is determined only by the width of the slit at the entrance and the exit, so that the resolution does not decrease.

As can be seen from the above, the achievement of the present invention involves the design of the diffraction lines of the concave grating to be used, and the optimum diffraction line design for this double monochromator uses the so-called holographic method. It can be executed by doing. Of course, the design of the diffraction engraved line requires computer calculation with the manufacturing parameters as variables, taking into consideration the imaging characteristics of the target double monochromator, but the details can be obtained from various documents. As an example of specific parameters, regarding the first diffraction grating: radius of curvature 4321, lattice constant 200 pieces / mm, arrangement parameter (see FIG. 2) r ₁ = 13641.2, r ₁ ′ = 2043.3, K ₁ = 70 ° (Degree) Depends on diffraction + 1st order; Second diffraction grating: radius of curvature 2188.5, lattice constant 204.0 lines / mm, r ₂ = 1707.5, r ₂ ′ = 1408.6 K ₁ = 90 ° Depends on diffraction + _1st order; The engraved line was produced by the following holographic method, and could be realized when the scanning wavelength range of the light beam used in the double monochromator was 500 to 2000 angstrom.

FIG. 2 shows the exposure system of the holographic method using the interference of spherical waves emitted from two light sources (C and D below) when the grating substrate is manufactured. The light source D shows the outline and parameters.
The light from the light source becomes an aspherical wave due to the off-axis reflection of the spherical mirror 6, and the condition that it interferes with the spherical wave from the light source C is adopted (see JP-A-61-80677 (JP-A-62-30201). ).

With the laser light wavelength = 441.6 nm and the radius of curvature of the exposing spherical mirror indicated by reference numeral 6 being 1000 mm, the parameters for the first diffraction grating are: p _c = 4009.9 mm p _D = 1998.1 mm q _D = 376.7 mm γ = 25 ° 53 'for the second diffraction _{grating: p c = 4005.2mm p D =} 2002.0mm q D = 371.6mm γ = 4 ° 35''δ = 20 ° 23' τ D = 44 ° 14 δ = 0 ° 34 ' τ _D = 33 ° 40 'In the figure, 6 is a spherical mirror, 7 is a diffraction grating substrate, and C and D are laser light source points.

To. Effects of the Invention In addition to the effects described above, the effects and applications of the present invention can also be used as a bandpass filter by using the first and second spectroscopes in a zero-dispersion arrangement. Further, the structure has a simple and practical effect as compared with a double monochromator using two plane diffraction gratings.

[Brief description of drawings]

FIG. 1 is a plan layout view of a double monochromator of the present invention. FIG. 2 is a plan view showing an exposure system for explaining the production of the concave diffraction grating mounted on the double monochromator of the present invention. FIG. 3 is a plan view of a double monochromator according to the prior art. In the figure, 1,1a ... inlet slit 2,2a ... first diffraction grating 3,3a ... intermediate slit 4,4a ... second diffraction grating 5,5a ... exit slit 6 ... spherical mirror 7 ... Diffraction grating substrate C, D ... Laser light source

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-56-46434 (JP, A) JP-A-56-112616 (JP, A) JP-A-61-176823 (JP, A) JP-A-57- 69221 (JP, A)

Claims (1)

(57) [Claims] 1. A double monochromator type concave diffraction grating spectrometer using two concave diffraction gratings as the first and second diffraction gratings, wherein the first and second diffraction gratings are formed by aspherical wave holographic exposure. At the same time, the concave diffraction grating spectroscope is characterized in that the diffraction lines of the two diffraction gratings are designed so as to compensate each other for the focal shift of each wavelength based on the rotational scanning of the first diffraction grating.