JPS6228844B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a spectrometer using a concave diffraction grating.

Generally speaking, it is desirable for a spectrometer to have little stray light, but in fluorescence spectroscopy, fluorescence is generally weak, so it is necessary that the excitation light be sufficiently strong, and of course the light source is a xenon lamp. Therefore, the level of stray light in the excitation spectrometer is quite high, and when this stray light is scattered by the sample, it is difficult to distinguish it from fluorescence, and in the end, it is difficult to distinguish it from fluorescence. This increases the background level of the fluorescent light and deteriorates the detection limit of the fluorescence. Therefore, an excitation spectrometer used in fluorescence spectroscopy is required to have a particularly low level of stray light.

The present invention was made with the aim of obtaining a concave grating spectrometer with a sufficiently lower level of stray light than conventional concave grating spectrometers, and when used as an excitation spectrometer in the above-mentioned fluorescence spectroscopy, it significantly improves the performance of the spectrometer. Sensitivity can be increased.

The main cause of stray light in a spectrometer using a concave diffraction grating is the reflection of the 0th-order diffracted light on the wall surface, and the other reason is the reflection of the diffracted light on the wall surface of the order of the opposite sign to that of the diffracted light that is actually being photometered. It's a reflection. In a conventional concave grating spectrometer, as shown in FIG. 1, the incident light I on the grating G and the diffracted light D from the grating are on a plane F perpendicular to the rotation axis A of the grating, that is, on the displacement plane of the grating. The entrance slit S1 and the exit slit S2 of the spectrometer were provided at the same height on the spectrometer peripheral wall W. With this configuration, the 0th-order diffracted light at G of the incident light I on the grating G, that is, the specularly reflected light R, is projected onto the spectrometer peripheral wall W, and re-enters the diffraction grating G where it is diffusely reflected. The specularly reflected light at G of this re-incident light returns to the vicinity of the entrance slit S1, so there is no actual damage. Some of the diffracted light on the grating G of the re-incoming light is focused on the exit slit S2, and its wavelength is different from that of the diffracted light on the grating G that is directly focused on the exit slit S2. This gives high stray light levels. Further, the diffusely reflected light on the wall surface W of the diffracted light D' having an order opposite to that of the diffracted light D of the incident light I on the grating G enters the grating G and is diffracted and reflected again. The diffracted light at this time generally returns to the entrance slit S1, so there is no actual damage, but some of the light re-reflected by the grating G has a wavelength that collects on the exit slit S2, which also increases the level of stray light. exhibits an effect. Since the main causes of stray light are as mentioned above, in order to eliminate stray light, the incident light I on the grating G is specularly reflected by the grating, and the diffracted light of a different order from that used for photometry is reflected on the spectrometer wall W. It is only necessary to prevent a part of the diffusely reflected light from entering the grating G again, being reflected or diffracted, and reaching the exit slit S2.

For this reason, in the present invention, as shown in FIG. 2, the entrance slit S1 and the exit slit S2 are positioned separately above and below the surface F by tilting a line connecting their centers. The plane F is a plane passing through the center of the diffraction grating G and perpendicular to the rotation axis A of the grating G, as in FIG. In this way, the reflected light R by the grating G of the incident light I on the grating G, and the diffracted light D' of an order different in sign from the diffracted light used for photometry, enter the spectrometer wall at approximately the same height as the exit slit S2. However, when the reflected light on the wall surface of these lights enters the grating G again and is reflected or diffracted, it will enter the spectrometer wall surface at approximately the same height as the entrance slit S1, and S2 is the height. Since these lights are different, these lights do not enter the exit slit S2, and the stray light level becomes approximately 0. The present invention will be explained below with reference to Examples. In the following figures, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and explanations thereof will be omitted.

FIG. 3 shows an embodiment of the invention. In this embodiment, black rough light-absorbing wall surfaces w are provided on both sides of the exit slit S2. In a spectrometer using an imaging diffraction grating, the entrance slit and the exit slit are in a conjugate relationship, and both the reflected light on the grating and the diffracted light that is not directly involved in photometry each form an image of the entrance slit, and these images The surface where these are connected forms an image surface that also includes an exit slit. The above-mentioned w is a surface close to the image plane and is light-absorbing. Therefore, on this wall surface, from the image of the entrance slit S1 formed by the reflected light and diffracted light by the grating G, toward the grating G. The amount of light reflected is extremely small.
This small amount of reflected light enters the grating G again and forms an image by reflection or diffraction on one virtual image plane f including the entrance slit S1. This image is an image of the portion of the wall w that is illuminated by the light. The virtual image plane f has a different vertical position from w, but is substantially parallel to it, and has an entrance slit S1 and an exit slit S2.
It is along the circle connecting the projection of onto the plane F and the center of the lattice G, that is, the Rowland circle. If the wall surface w is formed in this way, the image on w due to reflection or diffraction by the grating G of the entrance slit S1 will be minimized (because it is the sharpest). The image of the entrance slit S1 becomes blurred and enlarged whether the wall surface w is inside or outside the Rowland circle. The blurred and enlarged image of the image by the grid G is formed in front or behind the virtual image plane f including the entrance slit S1, so it becomes an even more blurred image on the virtual image plane f. Therefore, unless the entrance slit S1 and the exit slit S2 are separated by a considerable distance in the vertical direction, the lower part of the blurred image on the virtual image plane f will become stray light in the upper part of the exit slit S2. When the wall w is provided near the Rowland circle, the image on the virtual image plane f becomes sharp, so the vertical distance between S1 and S2 can be reduced. The benefit of this can be seen from FIG. Figure 4 shows the spectrometer of the present invention viewed from the side.
Since the aberration of the image on the exit slit S2 of the entrance slit S1 becomes large due to this, it is desirable that θ be small. The light that has reached the virtual image plane f is incident on the spectroscope wall (not shown) behind the entrance slit, where most of the light is absorbed and a part of it is scattered. Very little of the scattered light enters the grating G again, is reflected and diffracted there, and reaches the exit slit S2.

FIG. 5 shows an embodiment in which the light returning to the extremely small exit slit S2 is captured and almost completely absorbed, and a mirror M is placed diagonally upward at the virtual image plane f in FIG. The light from the grating G incident on the mirror is all reflected upward and absorbed by the optical trap T provided above the mirror M. A light trap may be placed directly at the mirror M.

Figure 6 shows optical traps T1 and T2 on both sides of the exit slit S2 instead of the black wall w in Figure 3.
is arranged. With this configuration, almost no light returns from the optical traps T1 and T2 toward the grating G, and even a very small amount of such light is reflected and diffracted by the grating G and converges at a position above the exit slit S2. It never enters the exit slit. Furthermore, the light collected above the exit slit S2 in this way can also be absorbed by the configuration shown in FIG. FIG. 7 is a modification of FIG. 6 in which mirrors M' are arranged diagonally downward on both sides of the exit slit S2, and an optical trap T' is arranged below them in an upward direction.

The spectrometer of the present invention has the above-described configuration, and by making the heights of the entrance and exit slits different, the structure is almost the same as a conventional spectrometer, but the level of stray light can be significantly reduced. . Furthermore, by providing light absorbing means near both sides of the exit slit, the level of stray light can be further reduced.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional concave grating spectrometer.
FIG. 2 is a perspective view of the arrangement of entrance and exit slits and concave diffraction gratings to explain the principle of the present invention, FIG. 3 is a perspective view of a spectrometer according to an embodiment of the invention, and FIG. 4 is a schematic side view of the same embodiment. 5 to 7 are perspective views of essential parts of spectrometers according to different embodiments of the present invention, respectively. G...Concave diffraction grating, S1...Entrance slit, S2
...Exit slit, w...Light-absorbing wall surface, T, T1,
T2...Light trap.

Claims (1)

[Scope of Claims] 1. A spectrometer characterized in that the entrance slit, the exit slit, and the concave diffraction grating are arranged so that a line connecting the centers of the entrance slit and the exit slit is inclined with respect to the displacement plane of the concave diffraction grating. 2. Spectroscopy according to claim 1, in which a light absorption band is arranged with the exit slit in the vicinity of the surface where the light enters the concave diffraction grating from the entrance slit and is reflected or diffracted to form an image of the entrance slit. vessel. 3. The spectrometer according to claim 2, wherein the light absorption band arranged across the exit slit is a light absorption wall surface. 4. A patent claim in which the light absorption band arranged across the exit slit is composed of an optical trap or a mirror that reflects light coming from a concave diffraction grating toward the optical trap, and an optical trap that absorbs the reflected light. The spectrometer according to item 2. 5. The spectrometer according to claim 2, wherein a light absorption means such as a light absorption wall or a light trap is provided at the position of the image formed by the concave diffraction grating of the light absorption band according to claim 2.