JPH0483131A - Square common pass interferometer fourier transform spectroscopic device - Google Patents

Abstract

PURPOSE:To perform space Fourier transform spectroscopic analysis by use of a square common pass interferometer by providing, in the light collecting position of the light from a sample, a slit having an opening for passing a part or the whole of the zero- order component of a Fraunhofer's diffraction image determined by an optical system. CONSTITUTION:The light from a face light emitting source S is collected by a lens L0 having a large light receiving aperture, and only the zero-order diffraction image of a Fraunhofer's diffraction image is transmitted and formed in a pinhole position P. This is converted to a parallel light flux by a lens L1 and entered into a square common pass interferometer, and the transmitted light of a splitter BS and the reflected light of the splitter BS are returned to the splitter BS through mirrors M3-M1, and in the reversed direction, respectively. The lights are entered to a two-dimensional light detector D as they are flat waves to form an interferogram on its detecting surface. This interferogram, in which interference stripes formed by the light of each wavelength component from the light source S are superposed to each other, is subjected to space Fourier transform, and its space frequency distribution is analyzed to determine the averaged spectrum distribution of the light source S.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spectroscopic device that obtains the spectral distribution of incident light by Fourier transforming a spatial interferogram formed by a square common path interferometer, and in particular,
This invention relates to a rectangular common-pass interferometer Fourier transform spectrometer that can take in light from a light source over a wide area and perform spectroscopy with high sensitivity, and is suitable for spectroscopic detection of extremely weak luminescence, such as bioluminescence, chemiluminescence, and fluorescence from biological samples. .

[Conventional technology]

Traditionally, spectroscopic devices can be roughly divided into spectroscopic devices that use a spectroscopic prism, a dispersive spectrometer that uses a diffraction grating, and a Michelson interferometer that forms a temporal interferogram while moving a moving mirror and converts the temporal signal into a Fourier method. A temporal Fourier transform spectrometer that obtains the spectral distribution of incident light by performing Fourier transform, and a temporal Fourier transform spectrometer that obtains the spectral distribution of incident light by Fourier transforming the 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

By the way, in such a spectroscopic device, in order to improve the spectral sensitivity, measures are taken to take in as much luminous flux as possible from the light source to be divided into 61 spectra. Representative examples are shown in FIGS. 15 and 16.

In FIG. 15, the light from the light emitter 1 is extracted by the slit 2, and in order to capture as much as possible of the light that has passed through the slit 2, the solid angle θ1 at which the light is captured is
is large, that is, the lens L with the smallest possible F number
1, the light from the slit 2 is taken in and converted into a parallel beam, and the solid angle θ that matches the parallel beam to the spectrometer is
The lens L2, which converts the light to 2, condenses the light to the rear focal point and makes it enter the spectrometer, thereby increasing the sensitivity of the spectrometer.

In addition, in the figure, slit 4 indicates the entrance slit of the spectroscopic device. In addition, in FIG. 16, the light emitter 1 is placed at the first focal point of the elliptical mirror 8, and the entrance slit 4 of the spectrometer is placed at the second focal point, and as in FIG. 15, the solid angle θ1 is large. The spectral sensitivity of the entire device is increased by taking in as much light as possible from the light emitter 1, converting it into a solid angle θ2 that matches the spectroscopic device, and making it incident thereon.

By the way, in a spatial Fourier transform spectrometer using a conventional square common path interferometer, as shown in FIG.
It is converted into a parallel beam of light, and is split into two by the beam splitter BS into transmitted light and reflected light, and the transmitted light is passed through mirror M3,
The light returns to the beam splitter BS via M2 and Ml, passes through it, is once focused at the rear focal point by the condenser lens L2, and enters a two-dimensional photodetector placed at a position conjugate with the mirror M2. . 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 opposite direction, is reflected there, is once focused at the rear focal point by the condensing lens L2, and is then reflected by the mirror. M2
The light is incident on a two-dimensional photodetector placed at a position conjugate to the above, but it interferes with the transmitted light, forming a spatial interferogram on the detection surface of the two-dimensional photodetector. By spatially Fourier transforming this and analyzing its spatial frequency distribution, the spectral distribution of the light emitter I can be determined.

[Problem to be solved by the invention]

By the way, for example, extremely weak light emitters such as bioluminescence, chemiluminescence, and fluorescence from biological samples are surface light emitters that do not emit light from one specific point on the sample but are distributed over a wide area. Figure 15 or 16
Even if an arrangement with a large solid angle as shown in the figure is used to capture as much weak light as possible, the light-emitting area is limited by slit 2 and light from other areas is not used for spectroscopy, so it is possible to perform spectroscopy with high sensitivity. That is difficult. Even if light is taken in from a wide area of the sample without limiting the emission area, there is no interference between the light from each emission point, so even if you try to perform spectroscopy using Fourier transform of the spatial interferogram, Improving sensitivity is difficult.

Furthermore, as will be described later, when comparing a temporal Fourier transform spectrometer and a spatial Fourier transform spectrometer, the spatial Fourier transform spectrometer is superior. Therefore, the 17th
It is possible to use a spatial Fourier transform spectrometer using a square common path interferometer as shown in the figure.
Conventional square common path interferometers do not necessarily have a satisfactory optical arrangement. In particular, using two lenses, a collimation lens L1 and a condensing lens L2,
The problem is that the two-dimensional photodetector must be placed at a position conjugate with the mirror M2.

The present invention was made in view of this situation, and
The purpose is to solve the problems of the prior art as described above and to provide an apparatus for sensitively performing spatial Fourier transform spectroscopy of light from a surface light emitter using a square common path interferometer. .

[Means to solve the problem]

The square common path interferometer Fourier transform spectrometer of the present invention which achieves the above object focuses light from a sample through a condensing optical system, and creates a Fraunhofer diffraction image determined by the condensing optical system at the condensing position. A slit having an aperture through which part or all of the 0-blown component passes is arranged, and a collimation optical system is arranged behind the slit to convert the light passing through the slit opening into a parallel beam of light, and this parallel light beam is converted into 2
a beam splitter that separates the beam, and first to third reflecting mirrors that sequentially reflect the parallel light beam that has passed through the beam splitter and return it to the incident surface of the beam splitter, the parallel light beam reflected from the beam splitter; are reflected in the reverse order and returned to the exit surface of the beam splitter again.
A parallel beam of light that first passes through the beam splitter, passes through the first to third reflecting mirrors, reaches the beam splitter, and passes through it again, and a parallel light beam that passes through the beam splitter again. Detection means is arranged to detect a one-dimensional or two-dimensional distribution image of interference fringes by interfering with the parallel light beam that is reflected by -, passes through the third and first reflecting mirrors, reaches the beam splitter, and is reflected again. The method is characterized in that the detected interference fringes are spatially Fourier transformed to determine the spectral distribution of light from the sample.

In this case, the opening of the slit may have a diameter that allows a portion of the first-order or higher-order components of the Fraunhofer diffraction image determined by the condensing optical system to pass through.

The condensing optical system is made up of a lens with a large light receiving aperture, and the collimation optical system is made of a lens with a small light receiving aperture, and the F of the collimation optical system is
The value is less than or equal to the F value of the focusing optical system, and the light beam from the sample entering the focusing optical system is converted into a smaller diameter beam, or the focusing optical system is a Cassegrain with a large light receiving aperture. The collimation optical system is a Cassegrain optical system with a small light receiving aperture, and the F value of the collimation optical system is equal to the F value of the condensing optical system.
It is desirable that the light flux from the sample entering the condensing optical system be converted into a light flux with a smaller diameter to increase the energy per unit area and perform spectroscopy.

[Effect]

In the present invention, light from a sample is focused through a focusing optical system, and an aperture is provided at the focusing position through which a part or all of the zero component of the Fraunhofer diffraction image determined by the focusing optical system passes through. A collimation optical system is placed behind the slit to convert the light that has passed through the slit opening into a parallel beam of light. without loss,
Moreover, the energy density can be increased by the area ratio of the condensing optical system and the collimation optical system, and the energy can be extracted as a plane wave. Therefore, compared to the conventional case where a sample of a surface light emitter is focused on a point or line and the luminous flux from that point is detected at a wide angle, it is possible to significantly increase the amount of light. Also,
The above collimation optical system also serves as the collimation optical system of the square common-path interferometer, and the condensing optical system of the conventional square common-path interferometer is omitted, so the attenuation of light by the optical system is halved, resulting in high sensitivity. A spectroscopic device can be realized. Furthermore, the degree of freedom in the arrangement position of the detection means for detecting the distribution image of interference fringes can be increased.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, an optical system for efficiently capturing light from a surface light emitter according to the present invention will be explained with reference to FIGS. 2 and 3.

As shown in FIG. 2, when a plane wave of coherent light is made incident on the lens LO, a Fraunhofer diffraction image is observed at the position of the focal length f.

This is called an Airy disk, and if a circular lens is used, circular concentric dark rings are formed, and the area within the first dark ring with a diameter corresponding to the lens aperture, that is, the Ω component, is the brightest. A wavefront equal to that when a plane wave is incident on an aperture having the size of the first dark ring is formed after the focal point. Now, the aperture diameter of the circular lens is Dr.
, given by focal length.

As shown in 31st ffl (A), a pinhole plate P with the diameter of the aperture is placed at the focal position of the lens LO, and the plane wave S1 heading in the optical axis direction is converted into a spherical wave 01 by the lens LO, and other incoherent light If the incident light is mixed with the spherical wave Q2, a divergent spherical wave Q2 is emitted from the aperture diameter of the pinhole plate P, and becomes a plane wave S2 at the lens L1. This means that
When a plane wave SO enters from the pinhole P side as shown in FIG.
This is the same as converting to 2. Therefore, it is determined by the aperture diameter, focal length, and wavelength of the lens LO (1)
By arranging a pinhole plate P having a size smaller than the first dark ring of the Fraunhofer diffraction image of the equation and using a lens L1 with an F value smaller than the lens LO, the light beam emitted from the surface light emitter can be Only the plane wave component S1 can be extracted as a plane wave without loss and with the energy density increased by the area distribution of the lens LO and the lens L1. Note that the opening diameter of the pinhole plate P may be made larger than the diameter of the first dark ring so that more than one component of the Fraunhofer diffraction image can be taken in. In this case, the pinhole plate P
The noise that enters due to the increase in the aperture diameter is superimposed on the plane wave S2, and becomes a component that reduces the contrast of an interferogram obtained by an interferometer, which will be described later. This is explained by analyzing the interference of the present invention as follows.

First, a coherent light source on the front focal plane of the lens L1 performs Fraunhofer diffraction on the rear focal plane of the lens L1, and the aperture surface distribution at that point performs Fresnel diffraction on the detector surface. Moreover, it can be analyzed as interference between two diffracted waves incident at an angle of θ, -0 with respect to the vertical direction of the front surface of the detector. As a result, interference is observed in the region of the Fourier transform image of the coherent light source image, and it is known that the contrast of the so-called interference fringes exhibits a maximum l. However, in the case of an incoherent light source that emits various wavelengths that are desired to be separated into spectra, if the source has a finite size, the contrast will decrease. Therefore, as the pinhole becomes larger, the energy of the incident light that can be used for interference can be increased, but the contrast of the interference fringes deteriorates.

The size of the pinhole can be determined by determining the contrast of the interference fringes and the S/N ratio, that is, the signal-to-noise ratio. As a result, it was found that the best S/N ratio was obtained by transmitting only the 0th order diffraction component of the Fraunhofer diffraction image by the lens L1. Therefore, detecting a part of the zero-blow component of the Fraunhofer diffraction image simply reduces the incident energy and deteriorates the S/N ratio. In addition, it is also possible to use a diameter that passes through the first-order or higher-order components of the Franhofer diffraction image.
Although the incident energy increases, it is not a good idea in terms of S/N ratio. Therefore, care must be taken when using part of the 0-blown component or up to the first order or higher.

Next, a square common path interferometer based on the present invention will be explained with reference to FIG. Pickpocket 7) The light beam from P is converted into a parallel light beam through the collimation lens L1, and is split into two by the beam splitter-BS into transmitted light and reflected light,
The transmitted light returns to the beam splitter BS via mirrors M3, M2, and Ml, passes through it, and enters the two-dimensional photodetector as a plane wave. 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 opposite direction, and is reflected there and similarly enters the two-dimensional photodetector as a plane wave. It interferes with the above-mentioned transmitted plane wave on the detection surface of a two-dimensional photodetector, forming a spatial interferogram (interference fringes). The difference from the conventional square common path interferometer shown in FIG. 17 is that the condenser lens is omitted. In this way, only one lens, the collimation lens L1, is required, and the loss of light amount on the lens surface is halved. Further, the arrangement position of the detection surface of the two-dimensional photodetector is no longer limited to one point that is conjugate with the mirror M2, which has the advantage of increasing the degree of freedom in arrangement and relaxing the arrangement accuracy.

FIG. 1 shows the basic configuration of a square common-path interferometer Fourier transform spectroscopy apparatus according to the present invention, which is constructed by combining the above-described capture optical system and a square common-path interferometer.

In the figure, S is a surface light emitter, LOlLl is a lens, P is a pinhole plate, and BS is a beam splitter - 1M1, M2, M3
is a mirror, and D is a two-dimensional photodetector.

The lens LO is a convex lens with a large light-receiving aperture, and a surface light emitter S of a sample to be subjected to spectroscopic measurement, such as a biological sample, is placed at an arbitrary position in front of the lens LO. The slit plate P is placed almost at the focal point position of the lens LO, and the slit width is one that satisfies the above-mentioned formula (1) or is large enough to capture first-order or higher Fraunhofer diffraction images, and The size is such that only the 0-blown component (straight component) of the Forfar diffraction image or some high-order components can be transmitted. Note that the slit width may be set to a size that allows only a part of the 0th-order diffraction device to pass through. Lens L1 is a small diameter lens whose front focus is at the pinhole position, and when the F value is less than the F value of lens LD, lens LO
This is to extract all the zero blow components formed at the pinhole position to obtain a plane wave. The lens L1 also serves as the only lens constituting the square common path interferometer shown in FIG. An inter-7 erodalum is formed on the detection surface.

In such a configuration, when the light from the surface emitter S is focused by the lens LO with a large light-receiving aperture and a Fraunhofer diffraction image is formed at the pinhole position, the pinhole diameter is (
Since the formula 1) is satisfied, only the 0th-order diffraction device of the Fraunhofer diffraction image from the surface emitting source S is transmitted, and it is converted into a parallel light beam by the lens L1 and enters the square common path interferometer. Then, an interferogram is formed on the detection surface of the two-dimensional photodetector. This interferogram is a superposition of interference fringes formed by light of each wavelength component from the surface emitting source S (the interval between interference fringes depends on the wavelength), so it is spatially Fourier transformed. By analyzing the spatial frequency distribution of the surface emitting source S
The averaged spectral distribution of can be obtained. In addition, if the pinhole diameter is larger than the size that satisfies equation (1), as described above, the noise that enters as the aperture diameter of the pinhole plate P increases has the effect of reducing the contrast of the interferogram. do.

In this way, in the present invention, the straight component from the surface emitting source S is collected by the lens LO with a large light receiving aperture, and the pinhole diameter is expanded to the diffraction limit to extract the straight component, which is different from the conventional method. In this way, it is possible to significantly increase the amount of light compared to the case where the light flux from a point light source or a line light source is detected at a wide angle.

In addition, by making the aperture of the lens LO larger than the L10 aperture and keeping the F value the same, the area ratio of both lenses increases the per unit area of the plane wave incident on the detection surface of the two-dimensional photodetector. Energy can be increased.

FIG. 5 is a diagram showing another embodiment of the present invention using a Cassegrain optical system. In this embodiment, light from a surface light emitter (not shown) is passed through the aperture 11 into the Cassegrain optical system 1.
0, a Fraunhofer diffraction image is formed at the position of the pinhole plate P by the convex mirror 13 and the concave mirror 12, only the straight component is extracted by the pinhole, and then the concave mirror 1
6. The diameter of the beam is reduced by the convex mirror 17, and the beam is extracted as a plane wave through the aperture 15, and as in the case of FIG. 1, the beam is made to enter a beam splitter, mirror, etc. (not shown). In this embodiment as well, the energy density can be increased by converting the luminous flux taken in by the aperture 11 into the diameter of the aperture 15.

Note that various lenses and reflecting mirror optical systems can be used instead of the imaging element LO1L1.10 of the capture optical system. For example, a camera lens with a large aperture and small F number,
A microscope objective lens, a telescope objective lens, a Cassegrain objective lens, and an eyepiece lens having a small diameter and a large numerical aperture may be used in appropriate combination.

Furthermore, in the present invention, various known two-dimensional photodetectors can be used, and their configurations can be broadly classified into solid-state image sensors and photoelectric conversion image sensors. Examples of solid-state image sensors include a parallel independent processing photodiode array shown in FIG. 6, and a charge-coupled device (CCD) type image sensor 1 shown in FIG.
Furthermore, a field effect transistor (MOS) shown in FIG.
) type image sensor.

The parallel independent processing photodiode array is one in which photodiodes 100 having a photovoltaic effect are arranged in an array as shown in FIG. 6, and wired so that the output of each photodiode can be directly taken out. Since the signal can be extracted independently from each photodiode, it is possible to access a specific photodiode as needed, and to separate the signal with background light removed (AC component signal) and the signal without background light removed (DC component signal). It is possible to perform parallel and independent processing of the signals from each photodiode, such as switching between signals.

As shown in Figure 7, the CCD type image sensor is
For example, a p-type layer is formed on an n-type silicon wafer by diffusion or epitaxial growth, and electrodes are further provided on top of the p-type layer so that picture elements 110 each consisting of three electrodes are arranged in a matrix. . By sequentially and selectively switching the voltage applied to the three electrodes that make up the picture element, a video signal is extracted while signal charges (e.g., holes) generated by incident light are sequentially transferred in one direction. has been done. Furthermore, by cooling the CCD, dark current and fixed noise at room temperature can be reduced.

As shown in Figure 8, the MO3 type image sensor is
The picture elements 120, in which two electrodes corresponding to the XSY coordinates constitute one unit, are arranged in a matrix, and furthermore,
Each picture element constitutes 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 pixel by the X- and Y-axis scanning signal generator shown in Figure 8, and the signal charge generated in the pixel by the incident light is transferred to the XSY-axis electrode. A signal current is extracted from the picture element whose voltage has become 0.

As a photoelectric conversion image sensor, an electrostatic focusing type MCP diode array as shown in Fig. 9 which combines a micro channel plate (MCP> and a diode array), a proximity type MCP diode array as shown in Fig. 10, and a type 11 The image orthicon shown in the figure, the vidicon shown in Figure 12, and the photonic microscope system (VIM) shown in Figure 13 that combines MCP and vidicon.
Further, there is a photo power mounting image acquisition system (PIAS system) as shown in FIG. 14, which combines an MCP and a semiconductor device detection element.

In the electrostatic focusing MCP diode array, as shown in FIG. 9, incident light causes a photocathode 130 to emit photoelectrons 136, which are accelerated and imaged by an electron lens system 131 and then enter an MCP 132.

The electrons are multiplied by the MCP 132, enter the phosphor screen 133, and emit light. The light emitted from the phosphor screen is configured to pass through an optical fiber 134 and enter a diode array 135 to output a video signal.

In the proximity type MCP diode array, as shown in FIG. 10, incident light causes photocathode 140 to emit photoelectrons, which are directly incident on MCP 141. Electrons are multiplied by the MCP 141, enter the phosphor screen 142, and emit light.

The light from the fluorescent screen 142 is configured to pass through an optical fiber 143 and enter a diode array 144 to output a video signal.

In the image orthicon, as shown in FIG. 11, photoelectrons 151 are emitted from a photocathode 150 in response to incident light. glass plate)
Collision with 153. As a result, target 153 to 2
Next, electrons are emitted, and the emitted electrons are collected on the target mesh, and a positive charge image corresponding to the 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 created near the target surface, which neutralizes the positive charges on the target surface. The electrons remaining after neutralization are density-modulated by the positive charge of the target, and further reach the vicinity of the electron gun 155 via an orbit almost the same as the original electron orbit. There are 2 near the electron gun.
A secondary electron multiplier 156 is arranged, which amplifies the returned electrons and outputs a video signal.

In the vidicon, as shown in FIG. 12, the target has a configuration in which a transparent conductive film 161 and a high resistivity photoconductive film 162 are stacked on a transparent face plate 160. When there is a pair of electrons and holes, the electrons pass through the transparent conductive film 161 and reach the signal electrode 16.
4, but the holes move to the surface of the photoconductive film on the scanning section side. Next, when the surface of the photoelectric film is scanned again by the electron beam, the electron beam flows into the target according to the magnitude of the surface potential due to the holes, passes through the signal electrode 164, and becomes a video signal.

The VIM system is a combination of a two-dimensional photon counter 170 and a low-afterimage vidicon 171, as shown in FIG. The light incident on the two-dimensional photon counter 171 generates photoelectrons on the photocathode 172, and these photoelectrons pass through the mesh 17.
3. The light enters an MCP (two-stage connected MCP in FIG. 13) 175 through an electron lens 174, is amplified, and hits a fluorescent screen 176 on the output surface to form a bright spot. This bright spot is imaged by the lens 177 on the photocathode of the vidicon with low afterimage, and a video signal corresponding to the incident light is obtained from the output of the vidicon.

As shown in Figure 14, the PIAS system consists of VIM
It is a combination of a two-dimensional photon counter 180 (however, in the 14th ylJ, it is a three-stage connected MCP) used in the system and a silicon semiconductor detector 181. M
The multiplied and accelerated photoelectrons from the CP 182 enter the semiconductor device detection element, are further multiplied by the electron bombardment effect at the time of incidence, pass through the resistance layer of the detection element 181, and pass through the four surrounding elements of the detection element. It is output from the electrode 183 as a current. By inputting these four outputs to a position calculation device (not shown), a position signal corresponding to the incident light can be obtained.

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

Next, the superiority of the spatial Fourier transform spectroscopy used in the present invention compared to the temporal Fourier transform spectroscopy will be explained.

Fourier spectroscopy, which Fourier transforms temporal interferograms, has superior characteristics over conventional dispersion spectroscopy, and has been developed and put into practical use as a bright, high-resolution device. In other words, ■The advantage of simultaneous photometry (multiplex advan)
superiority of luminous flux utilization), ■ superiority of luminous flux utilization (Jacquinot adva
It has been said that it is superior to the decentralized type due to two advantages:

Until now, Fourier transform infrared spectroscopy has been mostly used to measure light absorption, and has not been used to analyze weak light sources or luminescent bodies, so the above advantages have been experimentally confirmed. For a long time, people in this research field believed this as if it were a theorem.

However, in order to analyze extremely weak light such as biological photons, the spectroscopy must be truly excellent, which will quickly show up in the measurement results. In order to produce bright spectroscopy of biological photons that are too weak to be seen by the human eye, a comparative study of various spectroscopic methods revealed that they do not have the above advantages.

First, the advantage of simultaneous photometry (the advantage of the multi-pressure method)
This advantage is due to the fact that, where T is the total measurement time, the measurement time for one spectral element is T in temporal Fourier spectroscopy, and T/ in dispersive spectroscopy.
N (N is the number of spectral elements). ■FT-IR1■Wavelength scanning dispersive monochromator-1
■A comparison of three types of spectroscopy (polychromator) reveals that the above is incorrect.

Comparing FT-IR and wavelength scanning dispersive monochromators, FT-IR scans a movable mirror, detects interference fringes in the time domain from a detector, and obtains spectral information (spectral information) from the Fourier transform. ) is obtained. therefore,
Instead of scanning in the spectral domain, it scans in the interference domain and captures the observed wavelengths. This interference region information and spectrum information are mathematically linked, and if the time taken to capture all elements is the same for both, the results will be equivalent. That is, if the wavelength scanning monochromator is driven in the same way as the movable mirror of FT-rR, the observed wavelength will be captured in the spectral domain. The difference between the two is whether they are captured in the interference region or in the spectral region, and they are the same if the measurement time is the same. Therefore, the previous points are wrong.

In response to this, we invented and developed a polychromator (
In addition to Japanese Patent Application No. 1-208744), a simultaneous measurement type polychromator, which eliminates the exit slit and simultaneously observes many spectral elements using an array type detector, is a dispersion spectrometer, which has no scanning part and is capable of observing many spectral elements at the same time. The measurement time of the element is T, and the above ■FT-IR,
■Unlike a wavelength-scanning dispersive monochromator, the observation time can be extended by the number of spectral elements.

That is, the superiority of simultaneous photometry that has been pointed out in the past is an advantage that applies to a simultaneous measurement type polychromator without a scanning section. Stationary triangular common-path and square common-path interferometer Fourier transform spectroscopy has this advantage.

In other words, the superiority of simultaneous photometry is second to the superiority of luminous flux utilization (superiority of brightness,
The superiority of t) will be discussed. This advantage is that spectroscopy using an interferometer does not require a slit, and instead uses a large entrance hole (output hole) and an optical system with a large solid angle. First, considering the size of the light source, in a Michelson interferometer, the moving distance of the movable mirror determines the number of interference fringes to be moved, which determines the resolution of the device. The longer the optical path difference, the higher the resolution of the device. Now, suppose that the movable mirror moves a distance d that is the same as the size (width) of the diffraction grating of the dispersive spectrometer. wavelength λ
Considering the monochromatic light of , this means that 2d/λ interference fringes are obtained. At that time, the ability to detect interference fringes in the time domain with a photodetector depends only on the size of the center fringe (the size of the light source) of the concentric interference fringes formed by the Michelson interferometer. Need to detect light. This condition corresponds to the diffraction angle of a zero-order Fraunhofer diffraction image of a circular hole having an aperture diameter of d, a lens, or a diffraction grating. In other words, the size of the condenser mirror of the dispersive grating spectrometer, the size of the diffraction grating,
The size of the collimation lens of the Michelson interferometer,
Assuming that the optical path differences d are equal, the incident angle of the light source becomes the diffraction angle of the 0th order diffraction image. Therefore, ■When detecting interference fringes with a photodetector, a slit is placed on the incident side of the light source or in front of the photodetector in order to detect only the center fringe of the concentric interference fringes formed by the Michelson interferometer. It is necessary (it is wrong to say that slits are not necessary).

■Only the area that can be obtained is the size of the zero-order Fraunhofer diffraction image of an aperture that is equal to the size of the entrance lens, condenser mirror, or diffraction grating (it is incorrect to say that an entrance hole with a large area can be obtained).

Next, consider the slit effect. A Michelson interferometer extracts light from the center of concentric interference fringes and its vicinity using a circular hole. If this is made into a vertical slit like in a dispersive spectrometer, horizontal interference fringes will appear in the center of the concentric interference fringes.
When extracted with a photodetector, a cancellation of the intensity occurs. Therefore, only the size of the circular hole can be extracted. In a dispersive spectrometer, the slit width is related to the resolution of the spectrometer, but the vertical axis has an energy addition effect. Set the width of the slit to the size of the 0th order diffraction image, and set the height of the slit to h.
The energy addition effect is h/(λ/d). This means how many zero-order diffraction images can be included in the slit height, which is much larger than that of the Michelson interferometer. Triangular and square common path interferometers have interference fringes that are vertical line interference, so they have the energy addition effect of the slit, and are the same as dispersive spectrometers.

In other words, the following table shows the superiority of luminous flux utilization.

As described above, the square common path interferometer Fourier transform spectrometer of the present invention is superior to temporal Fourier transform spectroscopy in terms of both the superiority of simultaneous photometry and the superiority of luminous flux utilization. ing.

Moreover, since the light that is separated from a wide surface is introduced using the capture optical system shown in Figures 1 and 5, when the light flux from a point light source or a line light source is detected at a wide angle as in the conventional method. It is possible to significantly increase the amount of light compared to the previous model, and by reducing the number of lenses in the square common path interferometer from two to one, the attenuation of light due to the lenses is halved, making it possible to create a highly sensitive spectroscopic device. be able to. Furthermore, the degree of freedom in the arrangement position of the two-dimensional photodetector increases.

〔Effect of the invention〕

As described above, according to the present invention, light from a sample is focused through a focusing optical system, and a part of the 0-blown component of a Franhofer diffraction image determined by the focusing optical system or Arrange a slit with an opening that passes through the whole
A collimation optical system is placed behind the slit to convert the light that has passed through the slit opening into a parallel beam of light, so that only the plane wave component of the light beam emitted from the surface light emitter is condensed without loss. The energy density can be increased by the area distribution of the optical system and the collimation optical system and extracted as a plane wave. Therefore, compared to the conventional case where a sample of a surface light emitter is focused on a point or line and the luminous flux from that point is detected at a wide angle, it is possible to significantly increase the amount of light. In addition, the above collimation optical system also serves as the collimation optical system of the square common-path interferometer, and the condensing optical system of the conventional square common-path interferometer is omitted, so the attenuation of light by the optical system is halved and the high A sensitive spectroscopic device can be realized. Furthermore, the degree of freedom in the arrangement position of the detection means for detecting the distribution image of interference fringes can be increased.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the basic configuration of a square common-pass interferometer Fourier transform spectrometer according to the present invention, Figure 2 is a diagram for explaining a Fraunhofer diffraction image, and Figure 3 (A> is a pin A diagram for explaining the selective passage of diffracted components by a hole, FIG. 3 (B) is a diagram showing the state when a plane wave is incident on a pinhole, and FIG. FIG. 5 is a diagram showing the configuration of a common path interferometer, FIG. 5 is a diagram showing another embodiment of the present invention using a Cassegrain optical system, and FIGS. 6 to 14 explain examples of known two-dimensional photodetectors. Figures 15 and 16 are diagrams for explaining a conventional optical system that captures a light beam at a wide angle.
FIG. 7 is a diagram showing the configuration of a conventional square common path interferometer. LO, Ll...Lens, P...Pinhole, BS.
...Beam splitter-1M1, M2, M3...Mirror D...Two-dimensional photodetector, 10...Cassegrain optical system, 11.15...Aperture, 13.17...Convex mirror,
12.16...Concave mirror Fig. 3 (A) Fig. 2 Fig. 4 Fig. 5 Fig. 6 Fig. 9 Fig. 10 Fig. 7 Fig. 11 Fig. 12 Fig. 13 Fig. 14 Fig. 15 Figure 16

Claims (4)

[Claims] (1) A slit that collects light from the sample through a focusing optical system and has an aperture at the focusing position that passes part or all of the zero-order component of the Fraunhofer diffraction image determined by the focusing optical system. A collimation optical system is placed behind the slit to convert the light that has passed through the slit opening into a parallel beam, a beam splitter that divides the parallel beam into two, and a collimation optical system that converts the beam that has passed through the beam splitter into two. A first to third reflecting mirror that sequentially reflects the beam and returns it to the incident surface of the beam splitter, the first to third reflecting mirrors reflecting the parallel light flux reflected from the beam splitter in the reverse order and returning it again to the exit surface of the beam splitter. , and a third reflecting mirror are placed at each vertex of the quadrilateral, and the parallel light flux that first passes through the beam splitter, passes through the first to third reflecting mirrors, reaches the beam splitter, and passes through it again, and the first beam Detection means is arranged to detect a one-dimensional or two-dimensional distribution image of interference fringes by interfering with a parallel beam reflected by a splitter, passed through a third to first reflecting mirror, reached the beam splitter, and reflected again. , a square common path interferometer Fourier transform spectrometer characterized in that the detected interference fringes are spatially Fourier transformed to determine the spectral distribution of light from the sample. (2) The square common-pass interferometer Fourier according to claim 1, characterized in that the aperture of the slit has a diameter that allows passage of a part of first-order or higher-order components of the Fraunhofer diffraction image determined by the condensing optical system. Conversion spectrometer. (3) The condensing optical system consists of a lens with a large light-receiving aperture, and the collimation optical system consists of a lens with a small light-receiving aperture, and the F of the collimation optical system
The value is less than or equal to the F value of the condensing optical system, and the light flux from the sample incident on the condensing optical system is converted into a luminous flux with a smaller diameter to increase the energy per unit area and perform spectroscopy. The square common path interferometer Fourier transform spectrometer according to claim 1 or 2, characterized in that: (4) The condensing optical system consists of a Cassegrain optical system with a large light-receiving aperture, and the collimation optical system consists of a Cassegrain optical system with a small light-receiving aperture, and the F value of the collimation optical system is F value or less, and the light beam from the sample that enters the condensing optical system is converted into a light beam with a smaller diameter to increase energy per unit area for spectroscopy. Or the square common path interferometer Fourier transform spectrometer described in 2.