JPS6321128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a concave Echieret grating used in various spectrometers, in which each grating groove has a single blaze angle over the entire surface, and a method for manufacturing the same. .

Conventionally, a concave echelletz grating in which grating grooves are formed by a mechanical method has been used. However, this diffraction grating has the following drawbacks. The first problem is that it is similar to general concave diffraction gratings, but since the grating grooves are linear, it is difficult to eliminate various optical aberrations. Second, it is not possible to make the blaze angle of each lattice groove the same.To make the blaze angle uniform, the direction of the cutter must be continuously changed as the cutter is fed in a direction perpendicular to the lattice groove. However, in practice it is extremely difficult to do so. Therefore, at present, a convenient method is used in which the lattice plane is divided into several parts, the orientation of the cutter is kept constant during one division, and the orientation of the cutter is changed stepwise each time the division is changed. Therefore, the blaze angle is not single but is distributed over a certain range. For example, the wavelength efficiency characteristic of a tripartite-type concave Echieret grating in which the lattice plane is divided into three parts shows a maximum at three wavelengths as shown by dotted lines in FIG. 1, but the efficiency is low overall. The solid line in the figure shows the efficiency characteristic of the concave Ethieret grating according to the present invention, which has a peak at one wavelength λB, and has an overall higher efficiency than the conventional grating.

The first drawback of the conventional grating mentioned above can be solved by printing interference fringes on the grating substrate by a holographic method and etching them to form grating grooves. However, the grating grooves obtained by this method are ordinary concave gratings with a bilaterally symmetric cross section, and an Eschieret type concave grating cannot be obtained. For this reason, conventionally there has been no concave Echieret grating that has a single blaze angle and eliminates various aberrations.

Therefore, an object of the present invention is to provide an Ethieret grating having a single blaze angle, and also proposes a manufacturing method thereof. The present invention will be explained in detail below with reference to the drawings.

First, the meanings of some words used in this specification, which have already been introduced, will be explained with reference to FIG. Figure 2 shows one groove of the Esieret lattice, where G is the lattice plane, B plane of each groove is the groove plane, N is the normal to the lattice plane,
Let n be the normal to the groove surface, the angle α formed by Nn is the blaze angle, the angle i formed by the incident light with respect to the normal N to the lattice surface is the incident angle, and the angle δ between the emitted light and the normal N is the diffraction angle. . In blazed reflection, i-α=δ+α, and the blaze condition for light with wavelength λ is mλ=d
(sini-sin δ), m is the diffraction order, and d is the lattice constant (Fig. 2).

FIG. 3 is a diagram illustrating the positional relationship among the center of curvature C, Rowland circle Rc, entrance slit Si, exit slit So, etc., and the relationship among the blaze angle, incidence angle, diffraction angle, etc. in the concave Ethieret grating 1. The grid 1 is rotatable around an axis passing through the center Po and perpendicular to the plane of the drawing. Po is on Roland circle Rc,
If the grating 1 is placed along the Rowland circle at point Po, and the input slit Si and the exit slit So are fixed on the Rowland circle Rc at a position such that ∠SiPoSo=φ is around 70°, what are Si and So? Approximately satisfies the optical coupling condition (Se−ya−Namioka
mount), so we will explain the case using this mount. Now, in order to extract the light of wavelength λ to the injection slit So by blaze reflection, the grating 1 is set Po.
Consider the case where the center of curvature of the lattice 1 is moved from point C to point C' on the Rowland circle by rotating it by an angle αo around the axis. In this case, the normal lines of the lattice plane at each point P1, Po, and P2 of the lattice 1 intersect at the point C'. in this case
The incident angle at point Po is αo + φ/2, the diffraction angle δ is (φ/2) − αo, and mλ = d(sini
−sin δ) holds true. Also, at this time, the groove surface at point Po is perpendicular to the straight line PoC (the original Roland circle
(along Rc), so the blaze angle at this point is αo. Both ends P1 of the grid 1,
At point P2, the incident angle is slightly smaller than i at point Po, so the diffracted light passes through the exit slit So
Although it deviates slightly from the position of , the deviation is extremely small. Therefore, even when the grating 1 is tilted in this way, it can be considered that the light incident from the entrance slit Si is diffracted and converged at the position of the exit slit So. In this case, the blaze angles α1 and α2 at points P1 and P2 are because the angle of incidence at each point is different from i.
The blaze angle αo at point Po is slightly different. In Figure 3, the radius of curvature of the grating 1 is R = 150, the grating width W = 26 (all relative values), 2ε = 10°, and the lattice constant d =
8330 Å (1200 lines/mm), φ = 70°, i = 50°, wavelength λ = 3530 Å, αo = 15°, α1 = 15.15°, α2 =
The blaze angle is 14.82°, and the overall blaze angle α is 15°±0.2°. Since ±0.2° is buried in manufacturing errors, it is actually necessary that the blaze angle α be uniform over the entire surface of the grating. Figure 4 shows a cross-section of such a concave Ethelette lattice with the shape of the grooves enlarged and exaggerated. The line touches a small circle γ centered at C, and its radius γ is γ≈Rα.

Next, a method for manufacturing a concave grating as shown in FIG. 4 will be described. First, as shown in FIG. 5a, a coating 3 of a material having excellent ion etching properties, such as polymethyl methacrylate, is formed on a concave grating substrate 2, and a photoresist 4 is applied thereon. The substrate 2 is a glass plate polished to have a spherical, cylindrical, toric or other aspherical concave surface. The interference fringes of the original shape of the diffraction grating are printed onto the substrate thus prepared using a holographic method. The holographic method is a method in which mutually coherent point light sources are placed at the entrance and exit slit positions of the substrate 2 as shown in Figure 2, and interference fringes appear on the substrate surface. The optical system may be configured to divide the beam into two and converge each beam onto a point light source position using a lens. If the interference fringes thus generated are used as a diffraction grating, the light emitted from one light source will be diffracted and concentrated at the position of the other light source, so there will be no aberration. When the substrate 2 on which the interference fringes have been printed in the above manner is developed, a film 3 remains in a lattice pattern as shown in FIG. . In ion or electron etching, the etching rate is lowest in directions perpendicular and nearly parallel to the direction of incidence of ions, etc., and the etching rate is highest in a plane forming a certain angle with the incident particle beam. Therefore, as shown in FIG. 6, the particle beam I
When exposed to irradiation, etching is relatively fast in the direction perpendicular to the substrate surface, and etching is slow in the direction perpendicular to the grating groove surface, so etching progresses as shown in A, B, and C in the figure, resulting in asymmetrically shaped grooves. It is formed. In Figure 6, α is the blaze angle, so β with respect to the substrate normal N.
It is sufficient to irradiate the particle beam from an inclined direction. Here, β is an angle close to the angle formed by the groove surface B of the grating and the normal N to the grating surface, but if the direction of the ion beam, etc. is made parallel to the B surface, etching of the B surface itself will not proceed, so the ion It is necessary to determine β so that the beam is appropriately obliquely incident on the B plane, and since it varies depending on the type of particle beam, speed, particle density (beam intensity), substrate material, etching equipment, etc., it is necessary to determine it by experiment in advance. Find it by.

FIG. 7 shows a method for making β constant at each point on the lattice plane in a concave lattice. In the figure, reference numeral 2 denotes a masked substrate obtained by the method explained in connection with FIG. 5, which is set on the arm 5 so as to be rotatable in the direction of the arrow about its center of curvature C. 6 is one normal line of the substrate 2 beside the center of curvature C
It is a slit fixed at an angular distance of β from the PoC, and its length direction is 3
is parallel to the lattice of 7 is the ion source and slit 6
Although the substrate 2 is irradiated through the slit 6, it becomes a thin plate-like beam bundle and irradiates only the area including the position of Po on the substrate 2 and the vicinity thereof. With this configuration, each point on the board is adjusted by repeatedly rotating the board 2 back and forth around C.
All you have to do is pass through point Po.

Since the concave Ethierette grating of the present invention has a single blaze angle over the entire surface, it has higher overall efficiency than the conventional tripartite concave Ethieret grating, as shown in Fig. 1, and the blaze wavelength λB. Significant improvement in efficiency. Furthermore, the method of the present invention has the property of making it possible to maintain a constant blaze angle even if the grating lines are curved, so even if the grating mask is straight, it can be processed even if the grating mask is a curved grating made by a holographic method. A constant blaze angle can be easily and accurately obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing a comparison of the efficiency of the concave Ethierette grating according to the present invention and a conventional concave Ethierette grating, FIG. 2 is a diagram explaining the terms used in this specification, and FIG. , a diagram showing the relationship between diffraction angle, blaze angle, etc., 4th
The figure is a side view of a concave echeleton grating according to the present invention, FIG. 5 is an explanatory diagram of the initial step in the method of the present invention, FIG. FIG. 2 is a plan view of an apparatus for performing particle beam etching. DESCRIPTION OF SYMBOLS 1... Concave Ethielates lattice, 2... Grating substrate, 3... Coating.

Claims (1)

[Scope of Claims] 1. A concave Echieret grating characterized in that each groove surface is made up of grating grooves having the same blaze angle with respect to the normal to the grating surface. 2 Form a lattice groove in a thin film provided on a concave substrate, use this lattice-shaped thin film as a mask for the concave substrate, and align the concave substrate with the lattice lines of the thin film around the center of curvature along the circumference of the curvature. While moving in the orthogonal direction, a flat plate parallel to the lattice lines of the thin film lattice on the concave substrate is formed along a line passing through a point away from the center of curvature in a direction different from the normal direction of the concave substrate. A method for manufacturing a concave echestiol grating, characterized in that the surface of the concave substrate is etched by irradiating the concave substrate with a flux of ions or electrons.