JP2589704Y2 - Fourier transform interferometer - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a movable mirror used in a Fourier transform interferometer.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram showing an example of a conventional Fourier transform interferometer. In FIG. 3, the measured light P
_In is converted into two light beams by the half mirror 11, and each light beam is reflected by the mirrors 12 and 13, and the respective reflected lights are collected by the photodetector 15 via the lens 14.

Here, if the mirrors 12 and 13 are at the same distance from the half mirror 11, both light beams reinforce each other for light of all wavelengths. A difference is generated, and light satisfying x = nλ (n: an integer) reinforces each other. At this time, a light fringe appears, and light satisfying x = (n + ／) λ (n: an integer) is canceled out. At this time, a dark fringe will appear, and interference according to the optical path difference will be shown. A spectrum is obtained from the interference output figure (interferogram) when the optical path difference x is changed by using Fourier transform as an analysis means. Therefore, by moving one of the mirrors 12 and 13 in the direction shown by the arrow and changing the optical path difference between the two light beams, the interference output figure of the signal obtained from the photodetector 15 becomes the Fourier transform of the incident light. made of, in the Fourier transform interferometric spectrometer, performs the inverse conversion in the arithmetic unit 16, and to know the spectral distribution of the light to be measured P _in.

[0004]

However, in the Fourier transform type interferometer shown in the above prior art, an interferogram obtained by moving one mirror is Fourier transformed to obtain a spectrum. Is difficult to move in parallel due to the backlash and linearity of the slide. In this case, the stroke of the mirror is about 10 mm, and accuracy of the order of the wavelength of light is required. As a result, in order to move the mirror accurately, the movable part of the mirror is complicated and expensive. In addition, since linear motion has zero speed at both ends, acceleration is always required,
Energy loss was great.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a movable mirror which can change the optical path length with high accuracy by a simple structure and has a small energy loss in motion. An object of the present invention is to provide a Fourier transform interference spectrometer.

[0006]

According to the configuration of the present invention for solving the above-mentioned problem, in a Fourier transform type interference spectroscope, a movable mirror installed in one optical path is inclined with respect to a rotation axis. It is characterized by comprising a rotating inclined disk mirror and a conical mirror installed so that light reflected by the inclined disk mirror returns to the incident light direction. In addition, a configuration is provided in which a correction mirror is provided in front of the movable mirror so that light incident on the movable mirror is focused on the conical mirror.

[0007]

According to the present invention, the change in the optical path length is generated not by a linear motion but by a rotational motion.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the Fourier transform interferometer of the present invention. In FIG. 1, the same elements as those in FIG. 3 are denoted by the same reference numerals, and redundant description will be omitted. In FIG. 1, reference numerals 2 and 3 denote fixed mirrors and movable mirrors installed in respective optical paths of a two-beam interference system. Movable mirror 3
Is a tilted disk mirror 3 that rotates while tilting with respect to the rotation axis.
1 and a conical mirror 32 arranged so that the light reflected by the inclined disk mirror 31 returns in the incident light direction. 4
Reference numeral denotes a correction mirror arranged before the movable mirror 3 so that light incident on the movable mirror 3 is focused on the surface of the conical mirror 32. The inner surface of the conical mirror 32 is provided in a direction in which the reflected light from the inclined disk mirror 31 returns to the direction of the original incident light. Although the curvature of the cone changes depending on the height, the NA of this optical system is sufficiently small and the depth of focus is deep, so that the average curvature of the cone is sufficient as the curvature of the correction mirror 4.

In such a configuration, the half mirror 1
One of the lights split by 1 enters the moving mirror 3. The incident light is reflected by the correction mirror 4, is incident on the inclined disk mirror 31, and is reflected. The reflected light is reflected by the inner surface of the conical mirror 32, returns to the inclined disk mirror 31 again, is reflected, and is reflected by the half mirror 11 via the correction mirror 4.
Is incident on.

Here, as shown in FIG. 2, the inclined disk mirror 31 is rotated by a motor or the like. Due to the rotation of the inclined disk mirror 31, the light initially reflected at the point B of the inclined disk mirror 31 is reflected at the point C. As a result, even on the inner surface of the conical mirror 32, the light reflected at the point B 'is reflected at the point C'. The light reflected at point C 'returns to point C in the same way that the light reflected at point B' returns to point B and is reflected at point B and returns in the direction of the original incident light. , C and return to the direction of the original incident light. This is because when the inclined disk mirror 31 is tilted θ from the rotation axis, the light incident from the rotation axis direction is
It always reflects at the same angle regardless of the angle of rotation. At this time,
This is because が AB′B = ∠AC′C = 90 ° if the conical mirror 32 is installed around the optical axis at an opening angle of 2θ.

[0011] Further, △ ABB 'and 、 ACC' are similar, and AB <AC. That is, the optical path length can be changed by (AC-AB) × 2 by the rotation of the inclined disk mirror 31.

As described above, according to the above embodiment, the movable mirror of the Fourier transform interference spectrometer is configured to generate the change in the optical path length not by linear motion but by rotational motion, so that the speed is constant, that is, the acceleration is constant. Zero is sufficient, and it can be rotated by inertia, so there is little energy loss. In addition, there is little backlash or friction during exercise, the optical path length can be changed with high accuracy, and a motor for rotation is cheap and easily available.

In the above embodiment, if the beam to be measured is sufficiently narrow, the effect of the inner surface of the conical mirror 32 as a concave surface is reduced, so that the correction mirror 4 may be omitted.
Further, the correction mirror 4 may be a convex mirror having the same curvature as the cone of the conical mirror 32 instead of focusing on the conical mirror 32 (thinning the beam to be measured).
Further, the arrangement of the inclined disk mirror 31 and the conical mirror 32 of the movable mirror 3 is not limited to the above, and for example,
The conical mirror 32 may be below the inclined disk mirror 31.

[0014]

As described above in detail with the embodiments, according to the present invention, it is possible to change the optical path length with high accuracy with a simple structure and to reduce the energy loss of motion by a movable mirror. Can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an embodiment of a Fourier transform interferometer of the present invention.

FIG. 2 is a view showing the operation of a movable mirror used in the apparatus shown in FIG.

FIG. 3 is a conventional example.

[Explanation of symbols]

 Reference Signs List 3 movable mirror 4 correction mirror 31 inclined disk mirror 32 conical mirror

Claims (2)

(57) [Scope of request for utility model registration] In a Fourier transform interference spectrometer, a movable mirror provided in one optical path includes a tilted disk mirror that rotates while being tilted with respect to a rotation axis and light reflected by the tilted disk mirror. A Fourier-transform interference spectrometer, comprising a conical mirror disposed so as to return in the direction of incident light. 2. The Fourier transform interference spectrometer according to claim 1, wherein a correction mirror is arranged in front of the movable mirror so that light incident on the movable mirror is focused on the conical mirror. A Fourier transform interference spectrometer characterized by having a configuration including: