JP3134262B2 - Square common path interferometer Fourier transform spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectroscope for obtaining a spectral distribution of incident light by Fourier-transforming a spatial interferogram formed by a square common path interferometer, and more particularly to a spectroscopic device having a small area light source. The present invention relates to a square common-path interferometer Fourier transform spectrometer capable of taking in light with high sensitivity and capable of spectral separation with high sensitivity and suitable for spectral detection of extremely weak light emission such as bioluminescence, chemiluminescence, and fluorescence from a biological sample.

[0002]

2. Description of the Related Art Conventionally, spectroscopic devices are roughly classified into a spectroscopic prism, a dispersion type spectroscopic device using a diffraction grating, and a temporal interferogram formed by moving a moving mirror of a Michelson interferometer. Fourier transform of a temporal signal to obtain a spectral distribution of incident light by performing a Fourier transform, and a Fourier transform of a spatial interferogram formed by a two-beam interferometer such as a square common path interferometer. There is a spatial Fourier transform spectrometer that determines the spectral distribution of incident light. Among them, a spatial Fourier transform spectrometer using a conventional square common-path interferometer, as shown in an optical path diagram in FIG. 13, is obtained from a light source 1 placed at a front focal point of a condenser lens L1 having a focal length f. The light beam is converted into a parallel light beam by the condenser lens L1, and is split into transmitted light and reflected light by the beam splitter BS, and the transmitted light is split into mirrors M3, M2, M
1, the beam returns to the beam splitter BS, passes through the beam splitter BS, and once forms an image of the light source at the rear focal point by the imaging lens L2 having the focal length f, and then forms a divergent light beam to the mirror M2.
Or two-dimensional photodetector D arranged at a position conjugate with
Incident on. On the other hand, the light reflected by the beam splitter BS returns to the beam splitter BS via mirrors M1, M2, and M3 in the reverse direction, and is reflected there and reflected by the imaging lens L.
The light source image is once formed at the rear focal point by 2 and then enters the photodetector D arranged at a position conjugate with the mirror M2. Form a spatial interferogram. The interval between the interference fringes of the interferogram is determined by each inclination θ of the mirror M2 from the 45 ° plane. The spectral distribution of the light source 1 can be obtained by spatially Fourier-transforming the interferogram signal obtained by the one-dimensional or two-dimensional photodetector D and analyzing its spatial frequency distribution.

FIG. 14 shows an equivalent optical path diagram of this conventional square common path interferometer Fourier transform spectrometer.
The plane passing through the center of 2 and perpendicular to the optical axis is designated as plane A, the detection plane of photodetector D is designated as plane B, the distance between plane A and imaging lens L2 is a ', and the distance between imaging lens L2 and plane B is Assuming that the distance between them is b ', there is an imaging position relationship between the A surface and the B surface that satisfies the relationship of 1 / a' + 1 / b '= 1 / f. However, light source 1
And A surface are not in the image position relationship. The interference on the surface B is caused by the divergent light beams emitted from the separate light sources 1 on the axes which are inclined by 4θ and intersect at the position of the surface A because the light beams traveling in opposite directions are relatively inclined by 4θ by the mirror M2. Are converted into parallel luminous fluxes by separate condensing lenses L1, and these two plane waves are inclined by 4θ with each other and enter a common imaging lens L2,
After that, the light beam is once focused on the side focal point, and the divergent light beam forms an interference fringe which is mutually equivalent on the B surface (interference surface) conjugate with the A surface.

[0004]

As is apparent from the arrangement shown in FIG. 14, in the conventional square common path interferometer Fourier transform spectrometer, only when the light source 1 can be approximated to a point light source, the surface B (other than that) can be used. Also on another surface), interference fringes with high contrast (contrast ratio of approximately 1) can be obtained. However, when the light source 1 is a light source having a finite size, the light at each point on the surface A is a superposition of light from different points of the light source 1 because the surface A is not a geometric optical image of the light source 1. I have. Therefore, since the surface B is conjugate with the surface A, at each point of the surface B, light from the entire light source 1 is superimposed as in the case of the surface A. As the size of the light source 1 increases, the number of superpositions of light from different points increases. Therefore, although the surface B is a surface on which interference fringes are formed, the contrast decreases as the size of the light source 1 increases.

The present invention has been made in view of such a situation, and an object of the present invention is to reduce the contrast when the light source of the conventional square common-path interferometer Fourier transform spectrometer is enlarged. It is an object of the present invention to provide an apparatus for performing spatial Fourier transform spectroscopy of light from a surface light emitter with high sensitivity using a square common path interferometer.

[0006]

A square common path interferometer Fourier transform spectrometer according to the present invention, which achieves the above object, comprises a beam splitter, and a light beam transmitted through the beam splitter, which is sequentially reflected on the beam splitter and incident on the beam splitter. First to third reflecting mirrors for returning light beams reflected from the beam splitter in the reverse order, and returning to the emission surface of the beam splitter again; It is placed at the vertex, first passes through the beam splitter, passes through the first to third reflecting mirrors, reaches the beam splitter, transmits the beam again, and first reflects the light from the beam splitter to the third to first reflecting mirrors. A light beam which reaches the beam splitter through the beam splitter and reflects the light beam again is incident on the imaging optical system, and at a position substantially conjugate with the second reflecting mirror with respect to the imaging optical system. Serial allowed to interfere with both the light beam, the interference fringes 1
Detecting means for detecting a two-dimensional or two-dimensional distribution image is arranged,
In a square common-path interferometer Fourier transform spectrometer for spatially Fourier-transforming the detected interference fringes to obtain the spectral distribution of light from the sample, the beam splitter converges a light beam from the sample by another imaging optical system. And the other imaging optical system is arranged so that the imaging position is substantially at the position of the second reflecting mirror.

In this case, it is desirable that the sample has a spread perpendicular to the optical axis, for example, an extremely weak luminous body of a biological sample.

[0008]

According to the present invention, in a conventional square common path interferometer Fourier transform spectrometer, a light beam from a sample is converged by another image forming optical system and is incident on a beam splitter, and the image forming position is substantially square. Since this other imaging optical system is arranged so as to be located at the position of the second reflecting mirror of the common path interferometer, the luminous flux involved in the interference is not superposed from the whole sample as in the conventional apparatus, but is superimposed. , The aperture angle (light receiving angle) determined by the angle of inclination of the second reflecting mirror, the aperture of the imaging optical system located in front of the detecting means, and the distance from this optical system to the second reflecting mirror. Get higher. Also, the larger the sample, the higher the interference fringes obtained compared to the conventional apparatus. Further, since the apparatus of the present invention does not require any movable parts, highly sensitive spectral detection is possible with a simple apparatus configuration. Therefore, the square common-path interferometer Fourier transform spectrometer of the present invention is a spectrometer suitable for spectral detection of extremely weak light emission such as bioluminescence, chemiluminescence, and fluorescence from a biological sample.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an optical path diagram of one embodiment of a square common path interferometer Fourier transform spectrometer according to the present invention, and FIG. 2 is an equivalent optical path diagram thereof. Components similar to those in FIGS. 13 and 14 are denoted by the same reference numerals. It is. 1 and 2 is different from the conventional device shown in FIGS. 13 and 14 in that the light from the light source 1 is converted into a parallel light beam in the spectroscopic device of the present invention as in the conventional device. Instead of using the lens L1, an imaging lens L that forms an image from the light source 1 on the mirror M2 is used. Here, for simplicity, it is assumed that the focal length of the imaging lens L is f.

That is, a at the front side of the first imaging lens L
Of the light source 1 placed at a distance (a> f) is converted into a convergent light beam by the imaging lens L, and is divided into a transmitted light and a reflected light by the beam splitter BS, and the transmitted light passes through the mirror M3. Light is focused (imaged) at the position of the mirror M2. The optical distance from the imaging lens L to the mirror M2 is defined as b. The light beam reflected by the mirror M2 becomes a divergent light beam again, returns to the beam splitter BS via the mirror M1, and
The light passes through it and is focused again by the imaging lens L2 having the focal length f at a position conjugate with the mirror M2. At that position, a one-dimensional or two-dimensional photodetector D for detecting a spatial interferogram is arranged. On the other hand, beam splitter B
The light reflected by S is reflected by mirror M1 in the opposite direction,
The light is condensed at the position of the mirror M2, returns to the beam splitter BS via the mirror M3, is reflected there, forms an image on the detection surface of the detector D conjugate with the mirror M2 by the imaging lens L2, and interferes with the transmitted light. To form a spatial interferogram on the detection surface of the photodetector D. The interval between the interference fringes of the interferogram is determined by each inclination θ of the mirror M2 from the 45 ° plane. The spectral distribution of the light source 1 can be obtained by spatially Fourier-transforming the interferogram signal obtained by the one-dimensional or two-dimensional photodetector D and analyzing its spatial frequency distribution.

In this case, as in the prior art, the plane passing through the center of the mirror M2 and perpendicular to the optical axis is defined as the plane A, the detection plane of the photodetector D is defined as the plane B, and the distance between the plane A and the imaging lens L2. Is a 'and the distance between the imaging lens L2 and the B surface is b', the light source 1
1 / a + 1 / b = 1 / f between planes A and B. Also, an imaging position relation satisfying the relation of 1 / a '+ 1 / b' = 1 / f between planes A and B. It is in. Therefore, there is an image forming positional relationship between the light source 1 and the B surface which is the interference surface. Therefore, the light beams traveling in opposite directions are relatively inclined by 4θ by the mirror M2, and the divergent light beams emitted from the respective points of the separate surface light sources 1 on the axes which are inclined by 4θ and intersect at the position of the plane A are Is converted into a convergent light beam by separate imaging lenses L, and is converged so as to form an image on an image plane inclined 4θ back and forth with respect to the plane A at the position of the mirror M2. Then, this inclined light source image is set as a new set of point light sources, and the divergent light flux emitted from the corresponding specific point of each light source image is determined by the aperture of the imaging lens L2 and the distance a '(accordingly, the distance b'). The light enters the imaging lens L2 at the determined aperture angle (light receiving angle), and is condensed again at the corresponding point positions on those image planes sandwiching the B plane. Therefore, interference fringes are generated on the B plane based on the difference in distance between the two image planes.

[0012] The interference on the B side will be described a little more.
As shown in FIG. 3, a light source image formed near mirror B through mirrors M1, M2, and M3 is referred to as a light source image I, and mirrors M3, M3,
A light source image formed near the plane B via M2 and M1 is referred to as a light source image II. The light fluxes I, I coming out of one specific point of the light source 1 and condensed on the surface of the light source image I and the surface of the light source image II
I is indicated by a solid line and an alternate long and short dash line as shown. Therefore, on the surface B, a light beam I condensed on the light source image I surface and divergent again, and a light beam II condensed on the light source image II surface are incident, and these light beams I and II are the surface light source 1. Are emitted from the same point, and interfere with each other on plane B. Whether or not the interference is mutually reinforcing interference is determined by the distance Δ between the two image planes.
Is determined by whether or not is an integer multiple of the wavelength, so that equidistant interference fringes depending on the wavelength are generated on the B surface. On the surface B, the spread of these light beams increases as the distance from the center O increases, so that the contrast of the interference fringes decreases as the distance from the center O increases. Moreover, the spread of the light fluxes I and II on the B plane is determined by the opening angle (reception angle) determined by the tilt angle θ of the mirror M2, the aperture of the imaging lens L2, and the distance a '(therefore, the distance b'). Also, the range where interference fringes can be formed is
This is the area of the light source images I and II.

As described above, the luminous flux of the superimposition on the plane B is not superimposed from the entire light source 1 as in the conventional apparatus, but is the inclination angle θ of the mirror M2, the aperture of the imaging lens L2 and the distance a. '(Therefore, the light receiving angle) determined by the distance (the distance b'). Therefore, when the opening angle (4.theta.) Determined by the inclination of the mirror M2 is smaller than the angle at which the condensing lens of the conventional device looks at the finite light source, the present invention is used. In the case of, the contrast is higher. That is, in the device of the present invention, as the light source is larger, interference fringes having higher contrast than the conventional device can be obtained. In addition, the surface light source does not require each point to have coherence with each other. Further, since the apparatus of the present invention does not require a movable portion, highly sensitive spectral detection can be performed with a simple apparatus configuration. From the above characteristics, the square common path interferometer Fourier transform spectrometer of the present invention is a bioluminescence,
It is a spectroscopic device suitable for spectral detection of extremely weak luminescence such as chemiluminescence and fluorescence from biological samples.

In the present invention, various known one-dimensional or two-dimensional photodetectors D can be used, and the configuration is roughly classified into a solid-state image sensor and a photoelectric conversion image sensor. Examples of the solid-state image sensor include a parallel independent processing photodiode array shown in FIG. 4 and a charge-coupled device (CCD) shown in FIG.
Type image sensor, and a field effect transistor (MOS) type image sensor shown in FIG.

In the parallel independent processing photodiode array, the photodiodes 100 having a photovoltaic effect are arranged in an array as shown in FIG. 4 and wired so that the output of each photodiode can be directly taken out. . Since a signal can be extracted independently from each photodiode, it is possible to access a specific photodiode as necessary, and to obtain a signal from which background light is removed (AC component signal) and a signal from which background light is not removed (DC component). Signal) and the like, and can perform parallel independent processing of signals from the respective photodiodes.

As shown in FIG. 5, a CCD type image sensor is, for example, a p-type layer formed on an n-type silicon wafer by diffusion or epitaxial growth, and a three-electrode unit is formed on the p-type layer. The electrodes are provided such that the electrodes 110 are arranged in a matrix. By selectively switching the voltages applied to the three electrodes constituting the picture element sequentially, the video signal is extracted while the signal charges (for example, holes) generated by the incident light are sequentially transferred in one direction. Have been. Further, by cooling the CCD, dark current and fixed noise at normal temperature can be reduced.

As shown in FIG. 6, a MOS type image sensor has a matrix of picture elements 120 in which two electrodes corresponding to X and Y coordinates are one unit. Constitute a scanning circuit and a switch circuit made of MOS field-effect transistors. To extract a video signal from the sensor, a scanning pulse is applied to each picture element by the X and Y axis scanning signal generators in FIG.
The signal current is extracted from the picture element where the voltage of the Y-axis electrode becomes 0.

As the photoelectric conversion image sensor, an electrostatic focusing type MCP diode array as shown in FIG. 7 combining a micro channel plate (MCP) and a diode array, a proximity type MCP diode array as shown in FIG. , The vidicon shown in FIG. 10, the vidicon shown in FIG.
Photonic microscope system (VI
M system) and a photocounting image acquisition system (PIAS system) as shown in FIG. 12 in which an MCP and a semiconductor position detecting element are combined.

In the electrostatic focusing type MCP diode array,
As shown in FIG. 7, incident light is incident on the photocathode 130 at the photoelectrons 13.
The photoelectrons are accelerated and imaged by the electron lens system 131 and enter the MCP 132. MCP132
Then, the electrons are multiplied, enter the phosphor screen 133, and emit light. The light emitted from the phosphor screen passes through the optical fiber 134 and is incident on the diode array 135 to output a video signal.

In the proximity type MCP diode array, FIG.
The incident light causes photoelectrons to be emitted at the photocathode 140, and the photoelectrons are directly incident on the MCP 141 as shown in FIG. MCP1
At 41, the electrons are multiplied, enter the phosphor screen 142 and emit light. The light from the phosphor screen 142 passes through the optical fiber 143 and is incident on the diode array 144 to output a video signal.

In the image orchicon, photoelectrons 151 are emitted from the photocathode 150 in response to incident light as shown in FIG.
The laser beam passes through the target and collides with a target (a low-resistance glass plate having a thickness of about several μm) 153. As a result, the target 153
, Secondary electrons are emitted, and the emitted electrons are collected on a target mesh, and a positive charge image corresponding to incident light is formed on the target. When the target surface is scanned by the electron beam 154 in this state, a decelerating electric field is generated near the target surface, and the positive charges on the target surface are neutralized. The electrons remaining after the neutralization are density-modulated by the positive charge of the target, and reach the vicinity of the electron gun 155 via the orbit almost the same as the original electron orbit. A secondary electron multiplier 156 is arranged near the electron gun, and amplifies the returned electrons to output a video signal.

As shown in FIG. 10, the vidicon has a structure in which a target has a structure in which a transparent conductive film 161 and a high-resistivity photoconductive film 162 are stacked on a transparent face plate 160. When the incident light is present, a pair of an electron and a hole is generated, and the electron flows to the signal electrode 164 through the transparent conductive film 161, but the hole moves to the surface of the photoconductive film on the scanning unit side. Next, when the surface of the photoelectric film is again scanned with the electron beam, the electron beam flows into the target according to the magnitude of the surface potential due to holes, and passes through the signal electrode 164 to become a video signal.

The VIM system is a combination of a two-dimensional photon counter 170 and a low-image vidicon 171 as shown in FIG. The light incident on the two-dimensional photon counting tube 171 generates photoelectrons on the photocathode 172, and the photoelectrons pass through the mesh 173 and the electron lens 174 to generate an MCP (FIG. 11).
In this case, the light enters a two-stage connected MCP 175, is amplified, and hits a fluorescent screen 176 on the emission surface to form a bright spot. The bright spot forms an image on the photocathode of the low ghost vidicon by the lens 177, and a video signal corresponding to the incident light is obtained from the output of the vidicon.

As shown in FIG. 12, the PIAS system is a two-dimensional photon counter 180 used in the VIM system.
(However, in FIG. 12, the MCP is a three-stage connection MCP.) And a silicon semiconductor detector 181 are combined. The multiplied and accelerated photoelectrons from the MCP 182 enter the semiconductor position detecting element, are further multiplied by an electron impact effect at the time of incidence, and pass through the resistive layer of the detecting element 181 to form four photoelectrons around the element. The current is output from the electrode 183. By inputting these four outputs to a position calculation device (not shown), a position signal corresponding to the incident light is obtained.

Although a typical two-dimensional photodetector has been described above, a photodetector that can be used in a square common-path interferometer Fourier transform spectrometer in the present invention is as follows.
The present invention is not limited to those described above, and any device that can detect light two-dimensionally or one-dimensionally can be applied.

Next, i) a one-dimensional or two-dimensional photodetector is connected to a dispersion type spectroscope using a diffraction grating, and a high-sensitivity multi-wavelength simultaneous photometric type adopting a new spectral optical system for high sensitivity. Spectrometer (multi-channel spectrometer.
Filed as Japanese Patent Application No. Hei 1-208744. ) And ii)
Michelson interferometer Fourier, which forms a temporal interferogram while moving a moving mirror of a Michelson interferometer widely used for infrared spectroscopy and Fourier transforms the temporal signal to obtain the spectrum of incident light And iii) a spatial Fourier transform spectrometer which obtains a spectral distribution of incident light by Fourier-transforming a spatial interferogram using the square common path interferometer of the present invention. The comparison will be described.

(1) Features of Multi-Wavelength Simultaneous Photometric Spectrometer (Multi-Channel Spectrometer) By selecting a region where a multi-channel detector is installed, an observation wavelength region can be selected.

High sensitivity due to the superiority of simultaneous photometry.

It is possible to increase the width of the slit for incidence of the sample light and to improve the detection sensitivity by sacrificing the resolution.

The factor that determines the highest resolution is the size of the width of the diffraction grating, and since the achievable size is limited, the highest resolution is worse than that of the following Michelson interferometer Fourier transform spectrometer.

(2) Features of Michelson interferometer Fourier transform spectrometer The observation wavelength range cannot be selected by the same detector, and the entire sensitivity range of the detector is measured.

There is no advantage of simultaneous photometry (Japanese Patent Application No. 2-1).
Pointed out in 98760. Therefore, the sensitivity is the worst among the three spectroscopes.

The optical path difference between the two light beams of the Michelson interferometer was reduced, and the sample light incident pinhole (Japanese Patent Application No. 2-198 / 1990) was used.
760 points out the need for an incident pinhole. It is possible to improve the sensitivity by increasing the diameter of), sacrificing the resolution, and using the energy incident on the detector accordingly.

The factor that determines the highest resolution is the optical path difference between the two light beams, which can be larger than the width of the diffraction grating and the width of the multi-channel detector, which are factors of other spectrometers. Can be made.

(3) Features of the square common-pass simultaneous spectrometer (the present invention) The observation wavelength region cannot be selected, and the entire detector sensitivity region is measured.

The Fourier transform spectrometer for spatial interferogram has the advantage of simultaneous photometry (Japanese Patent Application No. 2-1.
Pointed out in 98760. ).

Since the width of the multi-channel detector and the number of channels which determine the highest resolution are smaller than the width of the diffraction grating and the number of grooves, it is the lowest resolution among the three spectrometers at present.

Compared with a conventional triangular common path interferometer or a square common path interferometer, which is a Fourier transform spectrometer for spatial interferogram, interference with good contrast can be obtained even if the sample light is large, so that the sensitivity is good. Although the resolution is lower than the other two spectroscopic devices, the detection sensitivity can be improved by taking a larger sample light instead.

As described above, the spectroscopy of the present invention is used as an apparatus for performing high-sensitivity spectroscopy on the emission spectrum of a surface-emission sample over the entire sensitivity of the detector by utilizing the advantages of simultaneous photometry because low resolution is sufficient. The device is suitable.

[0040]

As described above, according to the square common path interferometer Fourier transform spectrometer of the present invention, in the conventional square common path interferometer Fourier transform spectrometer, the light beam from the sample is converged by another imaging optical system. And the other image forming optical system is arranged so that the image forming position is substantially at the position of the second reflecting mirror of the square common path interferometer. Is not the superposition of the whole sample as in the conventional apparatus, but the inclination angle of the second reflecting mirror, the aperture of the imaging optical system located in front of the detecting means, and the distance from this optical system to the second reflecting mirror. Is determined by the aperture angle (light receiving angle) determined by the distance, and the contrast becomes higher. Also, the larger the sample, the higher the interference fringes obtained compared to the conventional apparatus. Further, since the apparatus of the present invention does not require any movable parts, highly sensitive spectral detection is possible with a simple apparatus configuration. Therefore, the square common-path interferometer Fourier transform spectrometer of the present invention is a spectrometer suitable for spectral detection of extremely weak light emission such as bioluminescence, chemiluminescence, and fluorescence from a biological sample.

[Brief description of the drawings]

FIG. 1 is an optical path diagram of one embodiment of a square common path interferometer Fourier transform spectrometer according to the present invention.

FIG. 2 is an equivalent optical path diagram of the apparatus of FIG.

FIG. 3 is a diagram illustrating a state of interference.

FIG. 4 is a diagram for explaining a configuration of a known parallel independent processing photodiode array.

FIG. 5 is a diagram illustrating a configuration of a known CCD image sensor.

FIG. 6 is a diagram illustrating a configuration of a known MOS image sensor.

FIG. 7 is a diagram for explaining a configuration of a known electrostatic focusing type MCP diode array.

FIG. 8 is a diagram for explaining a configuration of a known proximity MCP diode array.

FIG. 9 is a diagram for explaining a configuration of a known image orchicon.

FIG. 10 is a diagram for explaining a configuration of a known vidicon.

FIG. 11 is a diagram illustrating a configuration of a known VIM system.

FIG. 12 is a diagram illustrating a configuration of a known PIAS system.

FIG. 13 is an optical path diagram of a conventional spatial Fourier transform spectrometer using a square common path interferometer.

14 is an equivalent optical path diagram of the device of FIG.

[Explanation of symbols]

 L, L2: imaging lens BS: beam splitter M1, M2, M3: mirror D: one-dimensional or two-dimensional photodetector

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tsutomu Ichimura 1-1-20- Mukaiyama, Taishiro-ku, Sendai City, Miyagi Prefecture (72) Inventor Fumio Inaba 1-13-1 Yagiyama Minami, Taishiro-ku, Sendai City, Miyagi Prefecture ( 56) References JP-A-1-134217 (JP, A) JP-A-1-112122 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01J 3/45 G01N 21/76

Claims (3)

(57) [Claims] 1. A beam splitter, and first to third reflecting mirrors for sequentially reflecting light fluxes transmitted through the beam splitter and returning the reflected light fluxes to an entrance surface of the beam splitter, wherein the light flux reflected from the beam splitter is inverted. From the first to the third returning to the exit surface of the beam splitter after being reflected in the order of
Are arranged at the vertices of a quadrilateral, and the light flux that first passes through the beam splitter, passes through the first to third reflecting mirrors, reaches the beam splitter, passes through it again, and is reflected by the beam splitter first. A light beam that reaches the beam splitter via the third to first reflecting mirrors and reflects the light beam again is made incident on the image forming optical system, and the second light beam is transmitted to the image forming optical system.
Detecting means for causing the two light beams to interfere with each other at a position substantially conjugate with the reflecting mirror and detecting a one-dimensional or two-dimensional distribution image of the interference fringes, and performing a Fourier transform on the detected interference fringes spatially; In a square common-pass interferometer Fourier transform spectrometer for obtaining the spectral distribution of light from the sample, the light beam from the sample is converged by another imaging optical system and is incident on the beam splitter, and the image forming position is substantially A square common path interferometer Fourier transform spectrometer, wherein the another imaging optical system is arranged so as to be located at a position of a second reflecting mirror. 2. The Fourier transform spectroscopy device according to claim 1, wherein the sample is a sample that spreads perpendicular to the optical axis. 3. The square common path interferometer Fourier transform spectrometer according to claim 1, wherein the sample is a biological sample.