JPS6031252B2 - Concave grating monochromator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to a monochromator used in a spectroscopic device, and particularly to a concave grating monochromator suitable for vacuum ultraviolet spectroscopy.

■ Conventional technology Ultraviolet light, especially light in the wavelength region shorter than 20 m, has extremely low reflectance and transmittance on solid surfaces, so concave diffraction does not require a lens or concave mirror for spectroscopic measurements in this region. Grating spectrometers are commonly used.

A monochromator is a device that extracts an arbitrary wavelength from among the wavelengths contained in a light source.A concave grating monochromator usually consists of an entrance slit, an exit slit, a concave diffraction grating, and a wavelength scanning mechanism. There is.

The concave diffraction grating used in conventional monochromatic meters is a concave spherical surface with equally spaced straight grooves (the groove spacing and shape of a concave diffraction grating is such that the grating grooves are placed on a plane touching the concave surface at the center of the diffraction grating). (defined by projecting grooves).

Figure 1 shows the optical system arrangement of the Seya Namioka type monochromator, which is generally well known as a monochromator using a conventional concave diffraction grating. Both slits are fixed so that the angle at which the output slit 3 is viewed is about 70 degrees, and wavelength scanning is performed only by rotating the diffraction grating.

Although the present monochromator has an extremely simple configuration, it has the disadvantage that it is not suitable for high-resolution spectroscopic measurements because it has extremely large aberrations on the obtained spectrum. Figure 2 shows the optical system arrangement of a concave grating monochromator known as an Eagle-type monochromator.The angle of incidence and angle of diffraction are almost equal and their values are small, so there is relatively little aberration. Suitable for high-resolution spectroscopic measurements.

However, in the case of this arrangement, the wavelength scanning mechanism is complicated because it is necessary to rotate the concave diffraction grating 1 and simultaneously move the diffraction grating and the exit slit 3 during wavelength scanning. There are drawbacks such as difficulty in achieving linearity between the input wavelength and the wavelength obtained by the monochromator. Glue Object of the Invention The present invention uses a concave diffraction grating, in which the grating grooves are irregularly spaced and the grating groove shape is generally elliptical, in place of the conventional concave diffraction grating, thereby simplifying the wavelength scanning mechanism and allowing wavelength scanning to be performed easily. It is an object of the present invention to provide a high-performance concave grating monochromator that has linearity between the scanning input and the obtained wavelength and has even fewer aberrations than the conventional Eagle-type monochromator.

{4} General description of the invention As shown in FIG. ) is the light source position, the m-th order diffracted light with arbitrary wavelength o is placed at an arbitrary point C(rc,y)
A concave diffraction grating that converges without aberration is disclosed in Japanese Patent Application No. 48-4
It can be manufactured by the method described in the specification of No. 617, ``Method for manufacturing a diffraction grating''.

When using this diffraction grating in a monochromator, the entrance slit position A is required to obtain the sharpest spectrum in the direction of light dispersion.
The relationship between (r, Q) and the exit slit position B (r', 8) is as shown in the following equation. SaOS2Q+sa. S28-(COS
Qten COS8) ten K (Sinba ten Sin8) ni.
...(1} Here, K is a parameter that determines the amount of change in grating grooves, and if the grating groove spacing at the center of the concave diffraction grating is S. Then, the groove spacing is a linear function by Kmineko for each grating groove/book. Give the diffraction grating groove line conditions that vary.
The relationship between this K and the thermal aberration imaging point C(rc, cc) in FIG. 3 is expressed by the following equation. K=S (Cozy-hot.

S2y).・・・． - Rigidity Here, if r=r' and Q=8 as an approximation of the eagle-shaped arrangement, the relationship between r and Q is as follows. r C○S2QR-cosQ-K
sinQ. ...{3'
Figure 4 shows the relationship between the incident angle Q and the distance r between the center of the diffraction grating and the slit using K as a parameter. Corresponds to an analytical lattice.

On the other hand, by using a concave diffraction grating that converges the reflected light without aberration at point C in Figure 3, the incident slit position AH (rH, Q) and image position B are used to obtain the sharpest spectrum in the slit height direction.
The relationship of H(r' days, 8) is given by the following equation. Mother No. 10-
kuCOSQ+COS3)-tana(SinQten sin
8) = 0...[4] This is a parameter related to the curvature of the elliptical grating groove, and its relationship with the aberration-free imaging point C (rc, cc) in Fig. 3 is expressed by the following equation. It becomes like this.

n8niR1rceOSy
、． ．． 、． ．． [5}rjilnySimilarly to the above, rH=r
When Q=8, the relationship between rH and Q is as shown in the following equation.

rH-1.
．． ．． ... ■ R - cosQ + tanGSinQ The dotted line in Figure 4 is the relationship between Q and rH in equation {6', determined using a as a parameter, and in the figure, 8 = 0 is the same straight groove as the conventional concave diffraction grating. This corresponds to the case of a concave diffraction grating.

In a normal monochromatic meter, the entrance slit and the exit slit are arranged so as to extract the brightest spectrum in the wavelength dispersion direction (slit width direction).

In an Eagle type monochromator using a conventional concave diffraction grating, the distance between the slit and the diffraction grating changes significantly as the diffraction grating rotates for wavelength scanning (increasing the angle of incidence), and this change is reflected in the diffraction grating. It is not linear with respect to the lattice rotation angle. Therefore, in a practical Eagle-type monochromator in which the entrance slit and the exit slit are placed slightly apart in the wavelength dispersion direction, a mechanism for moving the exit slit at the same time as a wavelength scanning mechanism that moves the center of the diffraction grating as it rotates is required. . Furthermore, since the optimum spectrum imaging position in the slit height direction differs from the actual slit position, astigmatism corresponding to the amount of difference occurs in the spectrum image obtained on the exit slit. The present invention sets the amount of change in the distance between the grooves of the diffraction grating (parameter K) so that the amount of change in the distance between the diffraction grating and the slit is minimized within the wavelength range in which the monochromator is used, and The curvature (parameter) of the elliptical grating groove is determined so that the astigmatism is minimized at This provides a high-performance monochromatic meter with an extremely simple configuration.

In other words, since the amount of change in the distance between the diffraction grating and the slit has become extremely small (specifically, the degree of change is approximately 1/1000 of the concave curvature for a diffraction grating rotation angle of 50, and 4/I00 of the radius of curvature for loo) ), the movement mechanism of the diffraction grating becomes simple, and even in a slit arrangement where the entrance slit and the exit slit are separated, there is an advantage that both the entrance and exit slits can be fixed simply by rotating and moving the diffraction grating. Furthermore, when using a sine bar mechanism such as the conventional Seya Namioka monochromator for wavelength scanning, if the angle at which the diffraction grating is viewed from the input slit changes during wavelength scanning, the difference between the wavelength scanning input and the obtained wavelength will change. Although linearity is lost, if the amount of movement of the diffraction grating is sufficiently small compared to the radius of curvature, the difference between the wavelength scale as a scanning input and the actually obtained wavelength can be ignored in practice. Specifically, the amount of movement of the diffraction grating is 1'100 of the radius of curvature.
In Tochimuro degree, even if the ratio of the input/output slit interval to the radius of curvature is 1/5, the error from the linearity of the obtained wavelength is 1/10,000 degrees Fahrenheit of the wavelength. As a specific example, if the number of central grooves of the concave diffraction grating is 1200 grooves/mm and the wavelength range used is from 3 m to 200 nm,
The range of the diffraction grating rotation angle based on wavelength 0 is approximately 1.00.
If the value of K is 0.685, the distance between the slit and the center of the diffraction grating has a maximum value at approximately the center of the wavelength scanning range, and the amount of change within the scanning wavelength range is equal to the concave curvature. It is approximately 15/10000 of the radius. On the other hand, if the parameter 8 that determines the curvature of the grating groove is set to 20, the astigmatism becomes 0 at a rotation angle of about 60 degrees, and the astigmatism becomes almost minimum within the scanning wavelength range. Figure 5 shows the relationship between the angular center of rotation of the diffraction grating and the distance r/R from the center of the grating to the slit of a monochromator using the above concave grating, and the angular center of rotation of the diffraction grating and the center of the grating. This figure shows the relationship between the distance rH/R from the slit height direction to the spectral image position where the brightest iron occurs, and the relationship between r and R can be approximately approximated by the following equation. Long=.

-992 and OS (heart/3-960) ten. -〇1031-
...” (7} [5) Examples The present invention will be described in detail below with reference to Examples.

FIG. 6 shows a concave diffraction grating monochromator according to an embodiment of the present invention, in which a concave diffraction grating 10 with elliptical grooves at uneven intervals is placed on a movable table 12 restrained by a linear guide 11. The rotation axis of the diffraction grating includes an arm 13 parallel to the normal line to the center of the concave diffraction grating, and a connecting bar 18 having a unique angle Jo determined from the monochromator design conditions with respect to the arm 13. is fixed, and the arm 13 and the connecting rod 18 rotate together with the concave diffraction grating 10 while maintaining the angle Jo to each other.

The tip of the arm 13 is restrained by a tension spring 17 in a plane guide 16 fixed on a nut 15 fed by a screw 14. If the length of the arm 13 is p, then the arm 13 is connected to the screw 14.
The relationship between the angular center of rotation of the arm 13, that is, the rotation angle of the diffraction grating 10, and the feed amount x of the nut 15, with the rotation reference being perpendicular to the position perpendicular to A connecting rod 1 whose rotation center is on an extension line of and whose length is equal to that of the connecting rod 18.
9 and are rotatably connected to each other, and these connecting rods 18 and 19
This restricts the movement of the diffraction grating as it rotates.

The entrance slit 2 and the exit slit 3 are fixed at symmetrical positions with respect to the normal to the concave diffraction grating 10 at a rotation angle of 0,
The length of the connecting rods 18 and 1 is 1,/2, and the center of rotation of the rotation lattice. That is, when the connecting rods 18 and 19 are parallel, the distance between the center point of the input/output slit and the circle in the concave diffraction grating is 1,112, so 12 is the distance between the center point of the input/output slit and the connecting rod 19.
The distance 1 between the center of rotation of the diffraction grating and the center of the input/output slit corresponding to the center of rotation of the diffraction grating is given by the following equation. 1=1. COS (Koichishin.

) 112 ... (91 However, it's hot 1.<R
,12<Vine is good. In addition, if the rotation angle of the diffraction grating is the center o, the angle at which both the input and output slits look into the center of the diffraction grating is 6,
Assuming that the grating constant at the center of the concave diffraction grating is d, the relationship between the feeding amount x of the nut 16 as a monochromator wavelength scanning input and the wavelength input performed by the monochromator is as follows.

Entering = Jiku Sansan Toyo Needless to say, a cam mechanism that interlocks with the rotation of the diffraction grating can be used as the diffraction grating moving mechanism.

■Summary As explained above, according to the present invention, the problems of conventional concave grating monochromators such as low resolution, complexity of the wavelength scanning mechanism, and non-linearity of wavelength scanning can be solved with an extremely simple configuration. It can be solved.

The present invention has an extremely large effect in the field of vacuum ultraviolet spectroscopy, which is the main application of concave grating monochromators, but it can also be applied in the field of general visible ultraviolet spectroscopy as a high-performance monochromator that does not require a concave mirror or lens. It goes without saying that there is.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the optical system of a conventional Seya Namioka type concave diffraction grating monochromator, Figure 2 is an explanatory diagram of the optical system of a conventional Eagle type concave diffraction grating monochromator, and Figure 3 is an illustration of the aberration-free state of diffracted light. Figure 4 is an explanatory diagram of the positions of the entrance slit and the output slit in the concave diffraction grating that performs image formation.
The figure is a diagram showing the relationship between the rotation angle of the diffraction grating and the distance between the slits of the diffraction grating obtained by determining the optical system arrangement according to a specific example of the present invention. Figure 6 shows the optical system and wavelength scanning mechanism in the example of the present invention. Configuration diagram, in each figure 1 is a conventional concave diffraction grating,
10 is a concave diffraction grating capable of aberration-free imaging of diffracted light, 2 is an entrance slit, and 3 is an exit slit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A concave diffraction grating having a grating groove array that converges diffracted light of one arbitrarily selected wavelength without aberration at any point looking into the concave surface when a light source is placed at the center of curvature of the concave surface; A wavelength scanning mechanism capable of rotating the center of a concave diffraction grating about a straight line touching the grating groove as a rotation axis and simultaneously moving the rotation axis linearly in a direction perpendicular to the rotation axis; It is characterized by comprising a fixed entrance slit for taking in the light, and a fixed exit slit for extracting an arbitrary wavelength component of the light beam that passes through the entrance slit, enters the concave diffraction grating, is reflected and diffracted. Concave diffraction grating monochromator.