JPS6250771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to optical instruments, and more particularly to dual reflection optical systems.

The present invention is very effective for infrared spectral photometry. Furthermore, the present invention can be effectively used for high-speed analysis of complex gas mixtures, such as optical gas analysis, such as quantitative measurement of air pollution, which has become increasingly important as a part of environmental control methods. .

Currently, it is common practice in spectrophotometry to repeatedly pass radiation through an absorbing layer in order to increase the absorption measurement response. Therefore, in order to transmit the light beam from the light source through the absorption medium with minimum loss, a combination of a plurality of various reflecting mirrors is used. The practical scope of dual reflector systems is quite wide and includes unique high temperature devices and continuous spectrum generating instruments for analyzing spectra of difficult to volatilize compounds. All infrared spectrophotometers today are equipped with a long optical path cell or container for analyzing gases with very small concentrations or with very weak absorption bands.
Absorption cells or vessels of this type are used for both qualitative and quantitative analysis. It has an objective reflector with a focal length F on one side, two field reflectors arranged at an angle to each other on the opposite side, and an entrance slit adjacent to these reflectors. Dual-path optical system with exit slit (see, for example, Journal of the Optical Society of America, Vol. 3, 1940, p. 333)
It has been known. Planar reflectors are used as field reflectors, from which reflector lenses are placed several times the focal length.

In the system described above, since the intermediate image of the entrance slit is focused on a plane, the outermost rays are not compressed, so that double reflections result in a significant portion of the radiation hitting the edge of the reflector lens. The result is a scattering beyond the beam, ie the so-called vignetting phenomenon of oblique rays.

Furthermore, a double reflection optical system (e.g. , Journal of the Optical Society of America, 1942, Vol. 32, p. 285)
is also known. The reflecting elements adjacent to each other by the entrance slit and the exit slit are likewise formed as concave reflecting mirrors, all the reflecting mirrors having the same focal length, and the distance between the opposing reflecting mirrors being The distance is twice the focal length.

This known optical system based on the prior art forms an associated image system on the reflective surface of the reflector. In the optical system, the light beam passes in four paths, and in the direction of the light beam, a first concave reflector transmits the image of the entrance slit illuminated by the light source onto the surface of the opposite concave reflector. The opposing concave reflector forms an image of the first concave reflector on another concave reflector adjacent thereto. The other adjacent concave mirror is used to transmit an intermediate image of the entrance slit from the opposing concave mirror to the exit slit of the optical system.

By varying the angle between the concave reflector facing the entrance and exit slits, the second known system can be adjusted to allow the passage of more than four ray paths; A slight misadjustment can render the system unusable.

In prior art optical systems comprising similar concave mirrors arranged opposite a slit, the optical system's diameter is directly related to the geometrical dimension of the first concave mirror in the beam direction. It has been recognized that aperture ratios are inadequate to perform the necessary number of surveys in the infrared range of the spectrum.

It is therefore an object of the present invention to increase the aperture ratio of dual reflection optical systems.

According to the present invention, there is provided a dual reflective optical system having a plurality of opposing reflective members, one of the opposing reflective members being adjacent to an entrance slit and an exit slit, and the other being adjacent to two concave reflective mirrors. wherein the concave reflecting mirrors have different geometric dimensions, and the reflecting members adjacent to the slits are two identical reflecting mirrors and are symmetrical with respect to one of the slits. The distance between the group of identical reflecting mirrors and the concave reflecting mirror and the focal length of the small-sized concave reflecting mirror are such that the concave reflecting mirror of the large size A dual-reflection optical system is provided with a configuration that is approximately 1.5 times the focal length of the reflector.

In the optical system disclosed herein, the aperture ratio is increased and aberrations are reduced.
Additionally, the disclosed system provides an optical path length that is 1.5 times the optical path length of a container or cell with a fixed radiation path and of a particular size suitable for incorporation into a standard spectrophotometer. The rational arrangement of the reflectors allows standard cylinders to be used in the fabrication of cells instead of cells with complex shapes. This means that
This is especially needed when the gas cell is rated for use under gauge pressure. The disclosed optical system allows the light beam to be utilized to its fullest extent over the entire diameter of the cell and can be incorporated as a versatile multi-pass cell in all types of infrared spectrophotometers.

The dual-reflection optical system according to the invention will be described in more detail in connection with its embodiment in a dual-reflection cell.

A double reflection cell according to the invention has reflection members or units arranged opposite each other, one of which is adjacent to the entrance slit (FIG. 1) and the other of which is adjacent to two concave reflection mirrors. It consists of 3 and 4. Concave reflectors 3 and 4 have different geometric dimensions. That is, the geometric dimensions of the concave reflector 3 are substantially larger than those of the concave reflector 4, and the focal length of the concave reflector 4 is about 1.5 times that of the large concave reflector 3. Although the concave reflecting mirrors 3 and 4 are spherical in this embodiment, they may be aspherical. The reflecting elements or units adjoining the entrance slit 1 and the exit slit 2, respectively, consist of a group of two identical plane reflectors 5 and 6 symmetrical with respect to the exit slit 2. In order to correct slight aberrations in the present optical system, the reflective surfaces of the generally flat mirrors 5, 6 can be given a special shape, for example cylindrical or toroidal. The geometric center of the larger concave reflector 3 and the center of the exit slit 2 belong to one straight line, which is the optical axis of the optical system. The distance between the group of identical plane reflectors 5, 6 and the concave reflectors 3, 4 is about 1.5 times the focal length of the large concave reflector 3. Reflector 3, 4, 5,
6 are respectively holding bodies 7, 8, 9, 1
0 and is combined with a standard adjustment device 11. Reflector system 3, 4, 5, 6
is mounted in a closed housing constituted by a cylindrical part 12 and two lids 13,14. Windows 15 and 16 are provided in the lid 13 in front of the entrance slit 1 and the exit slit 2, respectively.
It is set in.

In the illustrated embodiment, the planar mirrors 5, 6 (FIG. 2) are generally rectangular and sized to fit within the diameter of the cylindrical portion of the housing of the optical system. The geometric dimensions of the entrance slit 1 and the exit slit 2 are the same.

The concave reflectors 3, 4 (FIG. 3) are likewise generally rectangular and are optimally housed within the housing of the optical system. That is, the large concave reflector 3 is located inscribed in the circle of the cylindrical part 12 of the housing, while the small concave reflector 4 is accommodated in the remaining space.

The illustrated dual reflection cell works as follows.

From a vertically elongated light source (not shown), the light beam passes through a window 15 (FIG. 1) and an entrance slit 1 to reach a concave reflector 3. The light beam is reflected by the concave reflector 3 and reaches the plane reflector 5. The plane reflector reflects the light beam towards the concave reflector 4. Thereby, the larger concave reflector 3 forms an enlarged image of the entrance slit 1 on the surface of the smaller concave reflector 4. Concave reflector 4 then directs the light beam to plane reflector 6, which reflects the light to concave reflector 3. The concave reflector 3 finally reflects the light beam onto the plane of the exit slit 2 and concentrates the light beam on the plane. Its dimensions are the same as the original dimensions. In this way, the rays pass through window 16.
The light exits the multiple reflection cell through the .

Since the optical system disclosed here is a reversible system, the light beam can also enter the reflection cell through the exit slit 2 (FIG. 2) and exit through the entrance slit 1. In this case, the mode of operation of the reflection cell is the same.

Concave reflector 4 (FIG. 3) provides a precise coincidence of the reflected image of large concave reflector 3. No light rays are scattered beyond the edge of the concave reflector 3. In this way, the vignetting phenomenon of oblique rays is completely prevented.

Since the large concave reflector 3 is inscribed within the cylindrical part 12 of the housing of the reflector cell, the aperture ratio of the system is utilized to the maximum.

Due to the structural features of the double-reflection optical cell described above, the reflectors 3, 4, 5, 6 can be adjusted individually and continuously in a simple and reliable manner. As a result of this, minor misadjustments of the system are not expected to affect the stability of its performance.

When compared to the prior art, the dual reflection optical system disclosed herein provides increased magnification,
Provides reduced aberrations, simplified alignment, and enhanced stability of reflector performance.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a double reflection cell in which the present invention is implemented; FIG. 2 is a cross-sectional view taken along the line - in FIG. 1; FIG. 3 is a cross-sectional view taken along the line - in FIG. FIG. In the drawing, 1 is an entrance slit; 2 is an exit slit; 3 and 4 are concave reflectors; 5 and 6 are flat reflectors; 7, 8, 9, and 10 are holders; Reference numeral 11 indicates an adjustment device; 12 indicates a cylindrical portion; and 15 and 16 indicate a window.

Claims (1)

[Scope of Claims] 1. A double-reflection optical system comprising: an entrance slit through which a light beam passes; a first concave reflector in the optical path of the light beam passing through the entrance slit; and a light beam reflected from the first concave reflector. 1.5 of the focal length of the first concave reflecting mirror.
a first planar reflector provided at a distance twice the distance from the first concave reflector; and a focal point provided adjacent to the first concave reflector and whose focal length is 1.5 times the focal length of the first concave reflector. a distance from the first concave reflector, but the geometric planar dimension is smaller than this, and the first concave reflector has a focal length that is 1.5 times the focal length of the first concave reflector. two concave reflecting mirrors, and a second concave reflecting mirror that is coplanar with the first planar reflecting mirror;
a second planar reflecting mirror provided on the optical path of the light beam reflected from the second concave reflecting mirror, and configured to reflect the light beam from the second concave reflecting mirror toward the first concave reflecting mirror; an output slit that is provided on the same plane as the slit and outputs the light beam reflected by the first concave reflector via the second planar reflector, and the first and second planar reflectors are A multiple reflection optical system comprising a group of identical reflection mirrors arranged symmetrically with respect to any one of the slits.