WO2014112027A1 - Fourier transform spectrometer - Google Patents

Abstract

A Fourier transform spectrometer pertaining to the present invention detects reciprocal vibrations of a moving mirror in an optical element for forming an optical path difference in an interferometer for obtaining an interferogram of a predetermined light, and controls the reciprocal vibrations of the moving mirror using self-excited signals based on the detection results. The present invention is thereby capable of providing a Fourier transform spectrometer in which the moving mirror reciprocally vibrates in a stable manner in response to noise from the exterior.

Description

Fourier transform spectrometer

The present invention relates to a Fourier transform spectrometer, and more particularly to a Fourier transform spectrometer that uses a moving mirror that reciprocally vibrates in the optical axis direction as an optical path difference forming optical element of an interferometer.

A spectrometer is a device that measures a spectrum representing a component (light intensity) of each wavelength (each wave number) in predetermined light (measurement light) to be measured. As one of the spectrometers, a Fourier transform spectrometer is known. The Fourier transform spectrometer generates interference light of predetermined light by an interferometer, measures the interference light, and Fourier-transforms the measurement result to obtain a spectrum of the predetermined light.

In a Fourier transform spectrometer, the output of the interferometer is a combined waveform obtained by causing a plurality of wavelengths of light included in the predetermined light to interfere at once with the interferometer, and is called an interferogram. The Fourier transform spectrometer obtains a spectrum of predetermined light by Fourier transforming the interferogram output from the interferometer. This interferogram has a profile that has one or a plurality of steep peaks in a predetermined range and a substantially zero level in the remaining range. The central peak among the one or more steep peaks is called a center burst.

The interferometer of such a Fourier transform type spectrometer includes a plurality of optical elements that form two optical paths between the incident position of the predetermined light and the interference position when the predetermined light is incident. The plurality of optical elements includes an optical path difference forming optical element that generates an optical path difference between the two optical paths by moving in the optical axis direction. As this optical path difference forming optical element, there is a moving mirror that moves in the scanning range along the optical axis direction at a constant speed.

∙ Normally, gas bearings and voice coil motors are used to move the movable mirror, so that the interferometer becomes relatively large. For this reason, in order to reduce the size of the interferometer, for example, a moving mirror that is driven by a parallel movement mechanism disclosed in Patent Document 1 has been proposed.

The parallel movement mechanism is disposed between the first and second leaf spring members arranged in parallel to face each other and between the first and second leaf spring members and at both ends thereof. First and second supports connected to each of the two leaf spring members, and provided on the surface of one end of the first leaf spring member, one of the first and second leaf spring members is bent and deformed. Accordingly, a piezoelectric element that translates one of the first and second support bodies in the opposing direction of the first and second leaf spring members is provided. And the movable mirror is arrange | positioned on the surface of the other end of the 1st leaf | plate spring member of a parallel displacement mechanism.

The parallel movement mechanism configured as described above is driven by a driving device connected to the parallel movement mechanism (piezoelectric element). This drive device performs PLL (Phase Locked Loop) control. In this PLL control, the frequency of a mechanical signal, which is a signal obtained by detecting the reciprocal vibration of the movable mirror by the parallel movement mechanism, is compared with a reference frequency of a constant frequency as a reference, and a voltage controlled oscillator (VOC) is set so that they match. : Adjust the oscillation signal output from the Voltage Controlled Oscillator) to the translation mechanism (piezoelectric element).

In the translation mechanism, when the piezoelectric element is expanded by the oscillation signal from the driving device, the first leaf spring member is deformed so as to be convex upward, and as a result, the movable mirror is displaced downward in the facing direction. When the piezoelectric element is reduced by the oscillation signal, the first leaf spring member is deformed so as to protrude downward, and as a result, the movable mirror is displaced upward in the facing direction. In the driving device, the reference frequency is set to a frequency (resonance frequency) at which the parallel movement mechanism (specifically, the first and second leaf spring members) resonates, so that the movable mirror disposed in the parallel movement mechanism has a displacement amount. Repeat large displacements (ie, reciprocate).

When the reciprocating vibration of the moving mirror in the interferometer is PLL-controlled as in the above Fourier transform spectrometer, noise from the outside, for example, noise due to voltage change, etc. is detected as a mechanical signal (reciprocating vibration of the moving mirror is detected. (The state in which the voltage-controlled oscillator outputs an oscillation signal having the same frequency as the reference frequency) is easily released. Thus, when the frequency of the oscillation signal output to the parallel movement mechanism changes in the PLL control and the reciprocating vibration of the movable mirror changes, the reciprocating vibration of the movable mirror is not stabilized.

JP 2011-250572 A

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a Fourier transform spectrometer in which a movable mirror stably oscillates against external noise.

A Fourier transform spectrometer according to the present invention detects a reciprocal vibration of a moving mirror of an optical path difference forming optical element in an interferometer for obtaining an interferogram of predetermined light, and uses the self-excited signal based on the detection result to detect the moving mirror. Controls reciprocating vibration. As a result, the present invention can provide a Fourier transform spectrometer in which the movable mirror stably oscillates against external noise.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

It is a block diagram which shows the structure of the Fourier-transform type spectrometer concerning 1st Embodiment. It is a figure which shows the structure of the interferometer and its periphery in the said Fourier-transform type spectrometer. It is an expansion perspective view which shows the structure of the light reflection mechanism in the said interferometer. It is sectional drawing which shows the mode of the reciprocating vibration of the movable mirror in the said light reflection mechanism. It is a block diagram which shows the structure of the moving mirror drive circuit in the said Fourier-transform type spectrometer. In the Fourier transform type spectrometer, it is a figure which shows an example of the moving mirror drive signal input into a parallel displacement mechanism, the detection signal of a photo reflector, and the output signal of the comparator into which the said detection signal was input. It is a block diagram which shows the structure of the light reception process part in the said Fourier-transform type spectrometer. It is a figure which shows an example of the interference waveform of the laser beam in the said Fourier-transform type spectrometer. It is a figure which shows an example of the waveform (interferogram) of the interference light of the predetermined light measured in the said Fourier-transform spectrometer. It is a figure which shows the relationship between the said interferogram and a window function. It is a figure which shows an example of the spectrum calculated | required in the said Fourier-transform type spectrometer. It is a block diagram which shows the structure of the moving mirror drive circuit and amplitude control circuit of a Fourier-transform type spectrometer concerning 2nd Embodiment. It is a figure which shows the mode of the response of the amplitude of a moving mirror at the time of changing the amplitude target of a moving mirror in the said Fourier-transform type spectrometer. It is a block diagram which shows the structure of the moving mirror drive circuit and amplitude control circuit of a Fourier-transform type spectrometer concerning 3rd Embodiment. It is a circuit diagram which shows the structure of the low-pass filter (IIR filter) which comprises the self-excitation signal generation part of the said Fourier-transform type spectrometer. It is a figure which shows the characteristic of the said low pass filter. It is a figure which shows an example of a square wave detection signal, and the output waveform of the said low-pass filter when this detection signal is input into the said low-pass filter. It is a figure which shows an example of the detection signal with which the noise was superimposed, and the said detection signal converted into the square wave signal by passing through a comparator. It is a figure which shows the relationship between the distance from a photo reflector to a measuring object, and the output voltage from a photo reflector. In the non-linear region in the relationship between the distance to the object to be measured and the output voltage, the detection signal obtained from the output of the photo reflector when the reciprocating vibration of one end of the translation mechanism is measured by the photo reflector, and this detection signal is low-pass It is a figure which shows the output signal of the said low-pass filter when inputting into a filter. It is a block diagram which shows the structure of the resonant frequency detection circuit of a parallel displacement mechanism. An example of a photoreflector detection signal when the amplitude of the moving mirror is observed while changing the frequency of the moving mirror drive signal that is the oscillation signal input to the translation mechanism, and the output of the comparator when this detection signal is input It is a figure which shows a signal.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. Further, in this specification, when referring generically, it is indicated by a reference symbol without a suffix, and when referring to an individual configuration, it is indicated by a reference symbol with a suffix.

FIG. 1 is a block diagram showing a configuration of a Fourier transform spectrometer according to the first embodiment. FIG. 2 is a diagram showing the configuration of the interferometer and its surroundings in the Fourier transform spectrometer. FIG. 3 is an enlarged perspective view showing a configuration of a light reflection mechanism in the interferometer. FIG. 4 is a cross-sectional view showing the reciprocal vibration of the movable mirror in the light reflecting mechanism. 4A shows a case where the piezoelectric element 155 expands, FIG. 4B shows a case where the piezoelectric element 155 contracts, and FIG. 4C shows how the light reflecting mechanism 15 vibrates. FIG. 5 is a block diagram showing a configuration of a moving mirror driving circuit in the Fourier transform spectrometer. FIG. 6 shows a moving mirror driving signal (excitation signal or self-excited signal) input to the parallel movement mechanism, a photoreflector detection signal, and a comparator output signal to which the detection signal is input in the Fourier transform spectrometer. It is a figure which shows an example. In FIG. 6, the upper graph is the moving mirror drive signal SG1 input to the translation mechanism, the middle graph is the photoreflector detection signal SG2, and the lower graph is the output signal from the comparator. SG3. The horizontal axis in FIG. 6 is time, and the vertical axis is voltage. FIG. 7 is a block diagram showing a configuration of a light receiving processing unit in the Fourier transform spectrometer. FIG. 8 is a diagram showing an example of an interference waveform of laser light in the Fourier transform spectrometer. The horizontal axis in FIG. 8 is the optical path difference, and the vertical axis is the amplitude.

A Fourier transform spectrometer (hereinafter abbreviated as “FT spectrometer”) 10 according to the present embodiment is an apparatus that measures a spectrum of predetermined light. The FT spectrometer 10 causes predetermined light to interfere with the interferometer 11, and Fourier transforms the waveform (interferogram) of the interference light obtained by measuring the interference light of the predetermined light. Obtain the spectrum.

More specifically, the FT spectrometer 10 samples a plurality of measurement data by sampling an electrical signal obtained by photoelectrically converting the interference light of the predetermined light generated in the interferometer 11 at a predetermined sampling timing. To get. Then, the FT spectrometer 10 obtains the spectrum of the predetermined light from the plurality of acquired measurement data (that is, the interferogram of the predetermined light) using Fourier transform. The FT spectrometer 10 of the present embodiment uses an integrated interferogram as a Fourier transform conversion target for obtaining a spectrum of predetermined light in order to improve the SN ratio and obtain a good accuracy result. This integrated interferogram is an interferogram obtained by integrating a plurality of interferograms of predetermined light generated in the interferometer 11.

Such an FT spectrometer 10 includes, for example, a measurement light source unit 50, an interferometer 11, a moving mirror control unit 60, a light reception processing unit 20, and a timing generation unit as shown in FIGS. 30, a control calculation unit 41, an input unit 42, and an output unit 43.

The measurement light source unit 50 irradiates the sample SM, which is an object to be measured, with a predetermined geometry. The measurement light source unit 50 includes, for example, a measurement light source 51 (see FIG. 2) and its peripheral circuits. The measurement light source 51 emits measurement light and irradiates the sample SM with the measurement light with a geometry of 45: 0 degrees, for example. The measurement light is light used for measuring the spectrum of the reflected light in the sample SM, and has a continuous spectrum in a predetermined wavelength band set in advance. The measurement light source 51 of this embodiment is, for example, a halogen lamp.

In the FT spectrometer 10 of the present embodiment, the measurement light emitted from the measurement light source 51 is incident on the surface (measurement surface SF) of the sample SM at an incident angle of 45 degrees as shown in FIG. The reflected light of the measurement light reflected on the sample SM (measurement surface SF) is measured from the 0 degree direction. That is, the component of the reflected light reflected in the normal direction (0 degree) of the measurement surface SF enters the interferometer 11 as the predetermined light.

In addition, although the predetermined light of this embodiment is reflected light of the measurement light reflected on the sample SM, it is not limited to this. The predetermined light may be, for example, transmitted light that has passed through the sample SM, or may be light that is re-emitted from the sample SM (for example, fluorescence emission) by irradiating the measurement light. Further, the predetermined light may be light emitted from the sample SM without being irradiated with the measurement light. That is, the FT spectrometer 10 can measure not only the reflected light but also the spectrum of transmitted light, re-radiated light, self-luminous light, and the like.

The interferometer 11 receives the reflected light of the measurement light reflected by the sample SM as predetermined light, and emits the interference light of the predetermined light. When the predetermined light is incident, the interferometer 11 branches the incident predetermined light into two lights (first branched light and second branched light). Then, the interferometer 11 advances (propagates) these branched first branched light and second branched light to two different paths (first optical path and second optical path), and then merges them again. At this time, in the first optical path and the second optical path, if there is an optical path difference between the branch point (branch position) of the predetermined light and the junction point (merging position, interference position) of the branched light, At this time, since a phase difference is generated between the first branched light and the second branched light, interference fringes are generated.

In the FT spectrometer 10 of the present embodiment, for example, a Michelson interferometer 11 as shown in FIG. 2 is used.

More specifically, the interferometer 11 includes a plurality of optical elements that form two optical paths, and a parallel movement mechanism (moving mirror driving unit) 150.

The plurality of optical elements includes a semi-transparent mirror (half mirror) 112, a fixed mirror 114, and a movable mirror 115 whose light reflecting surface moves in the optical axis direction. These optical elements 112, 114, and 115 are arranged in the interferometer 11 as follows.

The fixed mirror 114 and the movable mirror 115 are arranged so that the normals of the mirror surfaces are orthogonal to each other. The semi-transparent mirror 112 is arranged so that the normal line passes through the orthogonal point of each normal line in the fixed mirror 114 and the movable mirror 115 and intersects each normal line at an angle of 45 degrees.

The predetermined light incident on the interferometer 11 in which the plurality of optical elements 112, 114, and 115 are arranged in this way is divided into two lights (first branched light and second branched light) in the semi-transparent mirror 112. This branched light (first branched light) is a predetermined light reflected by the semi-transparent mirror 112 and enters the fixed mirror 114. Then, the first branched light is reflected by the fixed mirror 114 and returns to the semi-transparent mirror 112 again following the optical path that has come. On the other hand, the other branched light (second branched light) is predetermined light that has passed through the semi-transparent mirror 112 and enters the movable mirror 115. Then, the second branched light is reflected by the movable mirror 115, and reversely follows the optical path that has come to return to the semi-transparent mirror 112 again. The first branched light after being reflected by the fixed mirror 114 and the second branched light after being reflected by the movable mirror 115 interfere with each other by being merged by the semi-transparent mirror 112. In the interferometer (Michelson interferometer) 11 having such a configuration, the predetermined light enters the interferometer 11 along the normal direction on the mirror surface of the movable mirror 115, and the interference light of the predetermined light is transmitted from the fixed mirror 114. The light is emitted from the interferometer 11 along the normal direction on the mirror surface.

The interferometer 11 of the present embodiment is configured such that when the predetermined light is split into two lights (first branched light and second branched light) by the half mirror 112, the reflection side of the half mirror 112 reflected by the half mirror 112 ( Specifically, it further includes a phase compensation plate 113 that is disposed on the optical path of the first branched light reflected by the semi-transparent mirror 112 and directed toward the fixed mirror 114. That is, in the interferometer 11 of the present embodiment, the first branched light reflected by the semi-transparent mirror 112 is incident on the fixed mirror 114 via the phase compensation plate 113, reflected by the fixed mirror 114, and then phase compensated. The light enters the semi-transparent mirror 112 again through the plate 113. The phase compensator 113 has a phase difference between the first branched light and the second branched light resulting from the difference between the number of transmissions of the semi-transparent mirror 112 in the first branched light and the number of transmissions of the semi-transparent mirror 112 in the second branched light. Is an optical element used to eliminate (ie, compensate for a phase difference).

As described above, in the interferometer 11 of the present embodiment, the first branched light is half transmitted from the incident position of the predetermined light through the semi-transparent mirror 112, the phase compensation plate 113, the fixed mirror 114, and the phase compensation plate 113 in order. The first optical path reaching the transparent mirror 112 is followed. Further, in the interferometer 11 of the present embodiment, the second branched light follows a second optical path that reaches the semi-transparent mirror 112 again from the incident position of the predetermined light through the semi-transparent mirror 112 and the moving mirror 115 in order.

The interferometer 11 of this embodiment includes an incident optical system 111 that makes predetermined light incident on the semi-transparent mirror 112 as parallel light, and the predetermined light generated by causing the first and second branched lights to interfere with each other in the semi-transparent mirror 112. And an emission optical system 116 that collects the interference light and makes it incident on the first light receiving unit 21. The incident optical system 111 of the present embodiment is, for example, a collimator lens, and is disposed at an appropriate position between the measurement surface SF of the sample SM and the semi-transparent mirror 112. The exit optical system 116 of the present embodiment is, for example, a condenser lens, and is disposed at an appropriate position between the semi-transparent mirror 112 and the first light receiving unit 21.

The movable mirror 115 is one of the plurality of optical elements arranged in the interferometer 11 (included in the plurality of optical elements). For example, two optical paths (first optical paths) are generated by resonance vibration of the parallel movement mechanism 150. An optical path difference is generated between the optical path and the second optical path). The movable mirror 115 is reciprocated twice or more in the optical axis direction by the parallel movement mechanism 150 in order to generate a plurality of interferograms of predetermined light. That is, in the FT spectrometer 10, one interferogram is generated by the movable mirror 115 reciprocating once in the optical axis direction.

The parallel movement mechanism 150 is provided with a movable mirror 115, and reciprocates (reciprocates) the movable mirror 115 in the optical axis direction (vertical direction in FIG. 2). Examples of the movable mirror 115 attached to the parallel movement mechanism 150 include light reflection mechanisms disclosed in Japanese Patent Application Laid-Open Nos. 2011-80854 and 2012-42257. Note that in the light reflecting mechanism 15 described below with reference to FIG. 3, the part excluding the mirror surface region (moving mirror) 115 is the parallel moving mechanism 150.

The light reflecting mechanism 15 includes a pair of leaf springs (leaf spring members) including a first leaf spring 151 and a second leaf spring 152, and the leaf springs 151 and 152 to resonate the pair of leaf springs 151 and 152. A pair of supports (first support and second support) 153, 154, a piezoelectric element (plate spring drive unit) 155 that drives the pair of plate springs 151, 152, and one plate spring 151 And a movable mirror 115 formed in the above.

The first and second leaf springs 151 and 152 are arranged in parallel so as to face each other with a space therebetween.

The first support 153 is arranged at one end (the left end in FIG. 3) between the first and second leaf springs 151 and 152 so as to be connected to the first and second leaf springs 151 and 152. ing. The second support 154 has the first and second plates at the other end (the end opposite to the one end: the left end in FIG. 3) between the first and second leaf springs 151 and 152. It is connected to the spring. The first and second support members 153 and 154 are arranged in a state of being separated from each other between the first and second leaf springs 151 and 152.

The piezoelectric element 155 is disposed on the upper surface of the other end of the first leaf spring 151. More specifically, the piezoelectric element 155 is disposed above the second support 154 in the first plate spring 151 and on the surface opposite to the second support 154. As shown in FIG. 4A, the piezoelectric element 155 is configured by sandwiching a piezoelectric material 155a such as PZT (lead zirconate titanate), which is a piezoelectric material, by a pair of electrodes 155b and 155c.

The movable mirror 115 is provided on the upper surface at one end of the first leaf spring 151. More specifically, the movable mirror 115 is provided above the first support 153 in the first leaf spring 151 and on the surface opposite to the first support 153. The movable mirror 115 may be, for example, a mirror attached to the first plate spring 151, or a metal thin film such as aluminum formed (film formed) on the first plate spring 151, for example. Good.

The light reflection mechanism 15 configured as described above is manufactured by, for example, a MEMS (Micro Electro Mechanical Systems) technique.

In the light reflecting mechanism 15 having such a structure, as shown in FIG. 4A, when the piezoelectric element 155 expands, the first leaf spring 151 is deformed so as to protrude upward. As a result, the movable mirror 115 is While the first and second leaf springs 151 and 152 are displaced downward in the opposing direction, when the piezoelectric element 155 is reduced, the first leaf spring 151 is deformed so as to protrude downward as shown in FIG. 4B. As a result, the movable mirror is displaced upward in the facing direction. The light reflecting mechanism 15 repeats the displacement by resonance of the pair of leaf springs 151 and 152 in order to obtain a large amount of displacement, and causes the movable mirror 115 to reciprocate (reciprocate) along the optical axis direction. More specifically, when there is no distortion in the reciprocating vibration (reciprocating movement) at one end of the parallel moving mechanism 150, a signal (resonance frequency f ₀ ) of a frequency at which the pair of leaf springs 151 and 152 resonate (see FIG. Referring No. self励信6) is input to the piezoelectric element 155, the piezoelectric element 155 repeats expansion and contraction at the resonance frequency f _0. As a result, as shown in FIG. 4C, the movable mirror 115 has a maximum displacement amount from the origin position X0 around the origin position X0 (center position of the vibration amplitude) where the displacement amount becomes 0 (zero). Displaces in a substantially sinusoidal shape with the passage of time between the positions Xm and -Xm, and vibrates accurately at a specific frequency and with a constant frequency.

The moving mirror control unit 60 includes a moving mirror operation detecting unit 200 that can detect the operation of the moving mirror 115 in the optical axis direction, and a parallel moving mechanism 150 (light reflecting mechanism 15) based on the detection result of the moving mirror operation detecting unit 200. And a parallel movement mechanism control unit 610 for controlling. The moving mirror control unit 60 constitutes the moving mirror driving circuit shown in FIG. 5 together with the light reflecting mechanism 15 (the parallel moving mechanism 150 provided with the moving mirror 115).

The moving mirror operation detecting unit 200 is a sensor device that detects the movement of the moving mirror 115 (specifically, the movement of the moving mirror 115 through the movement of one end of the parallel movement mechanism 150 in the optical axis direction). In the example illustrated in FIG. 2, the moving mirror operation detection unit 200 includes a photo reflector as a detection sensor. This photo reflector includes a light emitting element that irradiates light to the back surface of one end of the parallel movement mechanism 150, and a light receiving element that receives light reflected by the back surface. The photo reflector detects the movement (reciprocal vibration in the optical axis direction) of one end (moving mirror 115) of the parallel movement mechanism 150 by detecting the amount of reflected light that changes according to the movement of the parallel movement mechanism 150. To do. The photo reflector outputs an analog signal (detection signal) synchronized with the movement of the parallel movement mechanism 150 (that is, the reciprocating vibration of the movable mirror 115). Therefore, one cycle of the output of the photo reflector corresponds to one reciprocation of the movable mirror 115, and one scan of the movable mirror 115 can be detected from the output of the photo reflector.

The detection signal (analog signal) output from the moving mirror operation detection unit 200 (specifically, a photo reflector) is input to the self-excited signal generation unit 612 via a comparator (not shown). This comparator is a hysteresis control comparator, and when the detection signal from the movable mirror operation detection unit 200 becomes equal to or greater than a predetermined amplitude (hysteresis voltage), a square wave (rectangular wave) corresponding to the detection signal from this comparator. Is output.

As shown in FIG. 5, the parallel movement mechanism control unit 610 includes an excitation signal generation unit 611, a self-excitation signal generation unit 612, and a signal switching unit 613, via the control of the parallel movement mechanism 150. The reciprocating vibration (reciprocating movement) of the movable mirror 115 is controlled.

The excitation signal generator 611 outputs an oscillation signal (drive signal) having a predetermined frequency (frequency) to the parallel movement mechanism 150 as an excitation signal. This excitation signal is an oscillation signal having a frequency (resonance frequency) f _{0 at which} the pair of leaf springs (first and second leaf springs) 151 and 152 of the translation mechanism 150 resonate or a frequency close to the resonance frequency f _0. is there. The resonance frequency f ₀ is a frequency obtained in advance by measurement or the like. The excitation signal generation unit 611 of the present embodiment is a rectangular wave generation circuit that outputs a rectangular wave having a desired frequency by counting a clock with a counter, for example. Alternatively, the excitation signal generator 611 uses a CR oscillation circuit using an RC circuit composed of a capacitor and a resistor, or an LC circuit composed of a coil and a capacitor such as a Hartley oscillation circuit and a Colpitts oscillation circuit. An LC oscillation circuit or the like may be used. The excitation signal generator 611 of the present embodiment outputs an oscillation signal having a resonance frequency f ₀ as an excitation signal (see the excitation state in FIG. 6). The excitation signal of this embodiment is a square wave signal.

The self-excited signal generation unit 612 uses the parallel oscillation mechanism 150 (specifically, a pair of electrodes 155b of the piezoelectric element 155) using an oscillation signal (drive signal) having a frequency based on the detection signal output from the moving mirror operation detection unit 200 as a self-excitation signal. To 155c). The self-excited signal generator 612 is parallel to the reciprocating vibration of the movable mirror 115 detected by the movable mirror motion detector 200 (specifically, the resonance vibration of the pair of leaf springs 151 and 152 (vibration at the resonance frequency f ₀ )). An oscillation signal whose phase is delayed by 90 ° with respect to the reciprocal vibration of the movable mirror 115 detected through the reciprocal vibration of one end of the moving mechanism 150 is output as a self-excited signal. This self-excited signal is a square wave signal having a resonance frequency f ₀ whose phase is delayed by 90 ° with respect to the reciprocating vibration of the movable mirror.

In this way, the self-excited signal whose phase is delayed by 90 ° with respect to the detection signal is input to the piezoelectric element 155 of the parallel movement mechanism 150, so that the movable mirror 115 moves in one direction or the other in the reciprocal vibration of the movable mirror 115. At the end position (position Xm or −Xm in FIG. 4C), the driving force to one end of the parallel movement mechanism 150 (the part to which the movable mirror 115 is attached) becomes zero, while the one end (the movable mirror) 115) is at an intermediate position (position where the moving speed is the highest: origin position X0 in FIG. 4C) from the one end (or the other end) to the other end (or the one end) in the vibration direction. The largest driving force is applied to the moving mirror 115) in the moving direction. For this reason, the amplitude (the amount of displacement in the optical axis direction) of the movable mirror 115 can be kept large in the reciprocating drive by the parallel movement mechanism 150 of the movable mirror 115.

The self-excited signal generator 612 of the present embodiment is, for example, a 90 degree phase shifter, but is not limited to this. The self-excited signal may be an oscillation signal whose phase is delayed by approximately 90 ° with respect to the detection signal (reciprocating vibration of the movable mirror 115). That is, as described above, when one end of the parallel movement mechanism 150 is at an intermediate position from one end (other end) to the other end (one end) in the vibration direction and in the vicinity thereof (up and down position with the origin position X0 in FIG. 4C). If a large driving force in the moving direction is applied to the one end portion and the displacement amount of the moving mirror 115 in the optical axis direction is within a predetermined range, the reciprocating vibration of the moving mirror 115 can be maintained. The phase delay with respect to may be shifted from 90 °.

The signal switching unit 613 includes a first switch element 614 disposed between the excitation signal generation unit 611 and the parallel movement mechanism 150, and a second switch disposed between the self-excitation signal generation unit 612 and the parallel movement mechanism 150. A switch element 615 and a switching control unit 616 that switches between the switch elements 614 and 615 are provided. The signal switching unit 613 transmits an oscillation signal (moving mirror drive signal) input to the parallel movement mechanism 150 between the self-excitation signal from the self-excitation signal generation unit 612 and the excitation signal from the excitation signal generation unit 611. Switch.

The switching control unit 616 inputs the self-excitation signal from the self-excitation signal generation unit 612 or the excitation signal from the excitation signal generation unit 611 to the parallel movement mechanism 150 (piezoelectric element 155) by switching the switch elements 614 and 615. Let More specifically, when the FT spectrometer 10 starts measuring predetermined light, the switching control unit 616 first turns on the first switch element 614 and turns off the second switch element 615. As a result, the excitation signal output from the excitation signal generator 611 is input to the translation mechanism 150. Then, the switching control unit 616 turns off the first switch element 614 and turns on the second switch element 615 at a predetermined timing, and receives the moving mirror drive signal input to the parallel movement mechanism 150 from the excitation signal. The self-excitation signal output from the excitation signal generator 612 is switched. In the present embodiment, as shown in FIG. 6, the predetermined timing is such that the movable mirror 115 in a stationary (stopped) state starts reciprocating vibration, and the amplitude of the reciprocating vibration becomes a predetermined magnitude and is stable. It's time. Details are as follows.

The switching control unit 616 determines whether or not the amplitude of the reciprocating vibration of the movable mirror 115 has reached a predetermined magnitude based on the detection signal input from the movable mirror operation detection unit 200. More specifically, when a detection signal (analog signal: see the middle graph in FIG. 6) output from the photoreflector is input to the switching control unit 616, the switching control unit 616 determines the width of the voltage of the detection signal ( (Corresponding to the amplitude) exceeds a predetermined value, it is determined that the reciprocating vibration of the movable mirror 115 has reached a predetermined magnitude. In addition, when the detection signal (square wave signal: see the lower graph in FIG. 6) is input via the comparator (hysteresis control comparator), the switching control unit 616, for example, When the amplitude appears continuously, it is determined that the reciprocating vibration of the movable mirror 115 has reached a predetermined magnitude. Further, the switching control unit 616 is configured to determine that the reciprocating vibration of the movable mirror 115 has become a predetermined magnitude when the frequency of the square wave signal starts to move at the same frequency as the frequency of the excitation signal. May be.

When the switching control unit 616 determines that the amplitude of the reciprocating vibration of the movable mirror 115 has reached a predetermined magnitude, the first switch element 614 is turned on and the second switch element 615 is turned off, so that the first switch The element 614 is turned off and the second switch element 615 is turned on. Thereby, the movable mirror drive signal input to the parallel movement mechanism 150 is switched from the excitation signal to the self-excitation signal.

Returning to FIG. 1, the light reception processing unit 20 receives the interference light of the predetermined light generated in the interferometer 11 and photoelectrically converts the electrical signal (in the interference light of the predetermined light). An electrical signal indicating a change in light intensity) is output. The light receiving processing unit 20 is a circuit that sequentially outputs a plurality of measurement data by sampling the electrical signal at a predetermined sampling timing. For example, as shown in FIG. 7, the light reception processing unit 20 includes a first light reception unit 21, an amplification unit 22, a band pass filter (Band Pass Filter) 23, and an analog-digital conversion unit (hereinafter referred to as “AD conversion”). 26).

The first light receiving unit 21 receives the interference light of the predetermined light generated in the interferometer 11, performs photoelectric conversion, and outputs an electrical signal (first light reception signal) corresponding to the light intensity in the interference light of the predetermined light. It is. The FT spectrometer 10 of the present embodiment uses, for example, light in the infrared region with a wavelength of 1200 nm or more, more specifically, light in the infrared region with a wavelength of 1200 nm or more and 2500 nm or less. Therefore, the first light receiving unit 21 is, for example, an infrared sensor including an InGaAs photodiode and its peripheral circuit. The first light receiving unit 21 outputs the light reception result to the amplification unit 22.

The amplifying unit 22 is an amplifier that amplifies the output (amplification result) of the first light receiving unit 21 with a predetermined amplification factor set in advance. The amplifying unit 22 includes, for example, an amplifier such as an operational amplifier and its peripheral circuit. The amplifying unit 22 outputs the amplification result to the band pass filter 23 (specifically, the high pass filter 24 constituting a part of the band pass filter 23).

The band pass filter 23 is a high pass filter (High Pass).
A filter 24 and a low-pass filter 25 are provided to pass only a desired frequency band in order to cut noise. The high-pass filter 24 is a circuit for passing a signal having a frequency equal to or higher than a predetermined cutoff frequency and cutting low-frequency noise, and outputs a filtered result to the low-pass filter 25. The low-pass filter 25 is a circuit for passing a signal having a frequency equal to or lower than a predetermined cutoff frequency and cutting high-frequency noise, and outputs the filtered result to the AD conversion unit 26.

The AD conversion unit 26 is a circuit that converts the output of the amplification unit 22 from an analog signal to a digital signal (AD conversion). The AD conversion timing (sampling timing) is the zero cross timing of the zero cross signal input from the timing generator 30 (specifically, the zero cross detector 37 of the timing generator 30). The AD conversion unit 26 outputs a digital signal as a result of the conversion to the control calculation unit 41.

The timing generator 30 generates a sampling timing for sampling the electrical signal in the light receiving processor 20 (specifically, the AD converter 26). The timing generation unit 30 includes, for example, a position measurement light source 31, a second light receiving unit 36, and a zero cross detection unit 37. As shown in FIG. 2, the timing generator 30, as shown in FIG. 2, uses a collimator lens 32, an optical multiplexer 33, an optical multiplexer to obtain interference light of the laser light emitted from the position measurement light source 31. A duplexer 34 and a condenser lens 35 are further provided.

The position measuring light source 31 emits monochromatic laser light having a known wavelength. The position measurement light source 31 of this embodiment includes, for example, a semiconductor laser that emits red laser light having a wavelength of 680 nm.

2, the collimator lens 32 and the optical multiplexer 33 constitute an incident optical system for causing the laser light emitted from the position measurement light source 31 to enter the interferometer 11 as parallel light. The optical multiplexer 33 is, for example, a dichroic mirror that reflects laser light and transmits predetermined light. The optical multiplexer 33 is disposed between the collimator lens 111 and the semi-transparent mirror 112 so that the normal line intersects the normal line (optical axis) of the movable mirror 115 at 45 degrees. The collimator lens 32 is a biconvex lens, for example, so that the laser light emitted from the position measuring light source 31 is incident on the optical multiplexer 33 arranged as described above at an incident angle of 45 degrees. Arranged at an appropriate position.

The optical demultiplexer 34 and the condensing lens 35 constitute an emission optical system for taking out the interference light of the laser light generated in the interferometer 11 from the interferometer 11. The optical demultiplexer 34 is, for example, a dichroic mirror that reflects interference light of laser light and transmits predetermined interference light. The optical demultiplexer 34 is disposed between the semi-transparent mirror 112 and the condenser lens 116 so that the normal line intersects the normal line (optical axis) of the fixed mirror 114 at 45 degrees. The condensing lens 35 is, for example, a biconvex lens, and condenses the interference light of the laser light emitted at an emission angle of 45 degrees in the optical demultiplexer 34 arranged as described above, and the second light receiving unit. 36 is incident.

When the optical elements such as the collimator lens 32, the optical multiplexer 33, the optical demultiplexer 34, and the condenser lens 35 are arranged in this way, the monochromatic laser light emitted from the position measuring light source 31 is converted into the collimator lens 32. And the optical path thereof is bent about 90 degrees by an optical multiplexer (a dichroic mirror in the example of the present embodiment), whereby the optical axis of the interferometer 11 (normal direction on the mirror surface of the movable mirror 115). Proceed along. Therefore, this laser light travels in the interferometer 11 like the predetermined light, and the interference light of the laser light is generated in the interferometer 11. Then, the interference light of this laser light is bent by about 90 degrees by an optical demultiplexer (in the example of the present embodiment) 34 and taken out from the interferometer 11. The extracted interference light of the laser beam is condensed by the condenser lens 35 and received by the second light receiving unit 36.

Returning to FIG. 1, the second light receiving unit 36 receives and photoelectrically converts the interference light of the laser light generated in the interferometer 11, and performs an electrical signal (second light reception) according to the light intensity of the interference light of the laser light. Signal). The second light receiving unit 36 is, for example, a light receiving sensor including a silicon photodiode (SPD) and its peripheral circuit. The second light receiving unit 36 outputs an electrical signal corresponding to the light intensity of the interference light of the laser light to the zero cross detection unit 37.

The zero cross detection unit 37 is a circuit that detects a timing (zero cross timing) at which the electric signal corresponding to the light intensity of the interference light of the laser beam input from the second light receiving unit 36 becomes zero. The zero cross detector 37 outputs a zero cross signal to the AD converter 26 at the zero cross timing.

The zero cross timing is a position on the time axis at which a predetermined reference voltage is set to a zero level and the electric signal is at the zero level. Details are as follows. FIG. 8 is a diagram illustrating an example of an interference waveform of laser light in the Fourier transform spectrometer of the present embodiment.

When the movable mirror 115 of the interferometer 11 is moved in the optical axis direction, the phase of the laser light that has returned from the semi-transparent mirror 112 to the semi-transparent mirror through the fixed mirror 114 is again transmitted from the semi-transparent mirror 112 through the movable mirror 115. As a result, the phase of the laser beam returned to the semi-transparent mirror is shifted again. For this reason, the interference light of the laser light becomes strong and weak in a sine wave shape according to the amount of movement of the movable mirror 115. At this time, when the movable mirror 115 of the interferometer 11 moves by a length that is ½ of the wavelength of the laser light, the phase of the laser light that has returned from the semi-transparent mirror 112 to the semi-transparent mirror through the movable mirror 115 is shifted by this movement. 2π before and after. For this reason, as shown in FIG. 8, for example, the interference light of the laser light repeatedly increases and decreases in a sine wave shape as the movable mirror 115 moves in the optical axis direction.

The zero cross detector 37 detects the zero cross of the electric signal that repeats the strength in a sine wave form. Then, the zero cross detection unit 37 outputs a zero cross signal to the AD conversion unit 26 at the detected zero cross timing. When this zero-cross signal is input, the AD conversion unit 26 samples and converts the electrical signal according to the light intensity of the interference light of the predetermined light input from the first light receiving unit 21 at the zero-cross timing. .

Returning to FIG. 1, the control calculation unit 41 controls each part of the FT spectrometer 10 according to the function of each part in order to obtain the spectrum of the predetermined light. The control calculation unit 41 is, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) or an EEPROM (Electrically Erasable Programmable Read) that stores various programs executed by the CPU and data necessary for the execution in advance. It is composed of a non-volatile memory element such as “Only Memory”, a volatile memory element such as a RAM (Random Access Memory) serving as a so-called working memory of this CPU, and a microcomputer provided with its peripheral circuits. The control calculation unit 41 may further include a relatively large-capacity storage device such as a hard disk in order to store data output from the AD conversion unit 26.

The control calculation unit 41 configured in this manner functionally executes a program when the control calculation unit 41 executes a program, so that a sampling data storage unit 411, a center burst position calculation unit 412, and an integrated interferogram calculation are performed. The unit 413 and the spectrum calculation unit 414 are configured.

The sampling data storage unit 411 stores measurement data regarding the interference light of the predetermined light output from the AD conversion unit 26. As described above, this measurement data is data obtained by sampling the electrical signal corresponding to the light intensity of the interference light of the predetermined light by the AD conversion unit 26 at the timing of the zero cross detected by the zero cross detection unit 37. It is.

The integrated interferogram calculation unit 413 obtains an integrated interferogram by integrating a plurality of interferograms obtained by continuously measuring predetermined light a plurality of times while performing alignment.

The center burst position calculation unit 412 obtains the position of the center burst from the measurement data stored in the sampling data storage unit 411 by a known conventional method.

The spectrum calculation unit 414 obtains a spectrum by Fourier-transforming the integrated interferogram obtained by integrating a plurality of interferograms in the integrated interferogram calculating unit 413.

The input unit 42 measures, for example, various commands such as a command for instructing the measurement start of the sample SM, and a spectrum such as an input of an identifier in the sample SM to be measured and a selection input of a window function used for Fourier transform. This is a device for inputting various data necessary for the operation to the FT spectrometer 10, such as a keyboard and a mouse.

The output unit 43 is a device that outputs commands and data input from the input unit 42 and a spectrum of predetermined light measured by the FT spectrometer 10. The output unit 43 is, for example, a display device such as a CRT display, LCD, organic EL display, or plasma display, or a printing device such as a printer.

Next, the operation of the FT spectrometer 10 configured as described above will be described.

In the FT spectrometer 10, before the measurement of the sample SM as a measurement target is started, first, the switching control unit 616 switches the first switch element 614 on and the second switch element 615 off, and generates an excitation signal. The excitation signal output from the unit 611 is input to the translation mechanism 150. Since the frequency of the excitation signal is a frequency at which the pair of leaf springs 151 and 152 of the translation mechanism 150 resonate and vibrate (resonance frequency f ₀ ), the translation mechanism 150 receives one end portion of the translation mechanism 150 by the input of the excitation signal. Begins to vibrate in the direction of the optical axis. That is, the translation mechanism 150 starts resonance vibration.

As shown in FIG. 6, when the amplitude of the reciprocating vibration of the movable mirror 115 gradually increases with time and becomes equal to or greater than a predetermined amplitude, the input from the inputted movable mirror operation detection unit 200 (photo reflector). Since the amplitude of the detection signal (the vertical width of the voltage) exceeds the hysteresis voltage of the comparator, the comparator outputs a square wave signal (detection signal) with a frequency corresponding to the frequency of the input detection signal (analog signal). start. When this detection signal (square wave signal) is input, the self-excitation signal generator 612 has a self-excitation signal (phase-shifted by 90 ° with respect to the input detection signal (reciprocating vibration of the movable mirror 115)). Output of a square wave signal is started.

When the switching control unit 616 determines that the amplitude of the reciprocating vibration of the movable mirror 115 has reached a predetermined magnitude from the input detection signal from the movable mirror operation detection unit 200, the switching control unit 616 turns off the first switch element 614. The second switch element 615 is turned on, and the moving mirror drive signal input to the parallel movement mechanism 150 is switched from the excitation signal to the self-excitation signal.

In this manner, the FT spectrometer 10 starts to reciprocate the moving mirror that was in a stationary (stopped) state when starting the measurement of the predetermined light using the excitation signal output from the excitation signal generator 611. After the reciprocating vibration of the moving mirror 115 is stabilized, the driving of the moving mirror 115 is switched to driving using an oscillation signal (self-excited signal) based on the reciprocating vibration of the moving mirror 115 (driving by self-excited oscillation). In the FT spectrometer 10, when the driving of the moving mirror 115 is switched from driving based on the excitation signal to driving by self-excited oscillation, the reciprocating vibration of the moving mirror 115 is stabilized. This is done.

The sample SM is set in the FT spectrometer 10, and then the measurement of the sample SM is started by the FT spectrometer 10. When the measurement is started, the measurement light source 51 emits the measurement light to the sample SM at an incident angle of, for example, 45 degrees by emitting the measurement light. Then, the reflected light of the measurement light reflected by the sample SM enters the interferometer 11 from the 0 degree direction as predetermined light.

The predetermined light incident on the interferometer 11 is received by the first light receiving unit 21 of the light receiving processing unit 20 as interference light of the predetermined light by the interferometer 11. More specifically, the predetermined light is converted into parallel light by the collimator lens 111, and is reflected and transmitted by the semi-transparent mirror 112 via the optical multiplexer 33, thereby being branched into first and second branched lights. The first branched light branched off by being reflected by the semi-transparent mirror 112 is incident on the fixed mirror 114 via the phase compensation plate 113, is reflected by the fixed mirror 114, and travels back in the opposite optical path to the semi-transparent mirror 112 again. Return. On the other hand, the second branched light branched by passing through the semi-transparent mirror 112 is incident on the movable mirror 115, reflected by the movable mirror 115, and returns to the semi-transparent mirror 112 by tracing back the optical path that has come. The first branched light reflected by these fixed mirrors 114 and the second branched light reflected by the movable mirror 115 merge at the semi-transparent mirror 112 and interfere with each other. The interference light of the predetermined light is emitted from the interferometer 11 to the first light receiving unit 21. The first light receiving unit 21 photoelectrically converts the incident interference light of the predetermined light and outputs an electrical signal corresponding to the light intensity in the interference light of the predetermined light to the amplification unit 22. The amplification unit 22 amplifies the electrical signal output from the first light receiving unit 21 (the electrical signal corresponding to the light intensity in the interference light of the predetermined light) with a predetermined amplification factor, and outputs the amplified signal to the AD conversion unit 26.

On the other hand, the interferometer 11 also captures a monochromatic laser beam emitted from the position measurement light source 31. This laser light enters the interferometer 11 via the optical multiplexer 33 and interferes with the interferometer 11 in the same manner as described above. The laser light that has become the interference light is received by the second light receiving unit 36 via the optical demultiplexer 34. The second light receiving unit 36 photoelectrically converts the incident interference light of the laser beam and outputs an electric signal corresponding to the light intensity in the interference light of the laser beam to the zero cross detection unit 37. The zero cross detection unit 37 detects the timing at which the electric signal corresponding to the interference light of the laser beam becomes zero as the zero cross timing, and outputs the zero cross timing to the AD conversion unit 26 as the sampling timing (AD conversion timing).

While the predetermined light and the laser light are respectively taken into the interferometer 11, the movable mirror 115 of the interferometer 11 is reciprocally oscillated (reciprocated) in the optical axis direction by driving by the self-excited oscillation described above. .

The AD conversion unit 26 samples the electrical signal corresponding to the light intensity in the interference light of the predetermined light output from the amplification unit 22 at the zero cross timing input from the zero cross detection unit 37, and converts the analog signal into a digital signal. A / D conversion is performed. Then, the AD conversion unit 26 outputs the electric signal of the digital signal after the AD conversion to the control calculation unit 41.

Here, FIG. 9 shows an example of the waveform (interferogram) of the interference light of the predetermined light actually measured in the Fourier transform spectrometer of the present embodiment. The horizontal axis in FIG. 9 is the optical path difference x between the first optical path and the second optical path, and the vertical axis is the amplitude Fm (x) of the interferogram. FIG. 10 shows the relationship between the interferogram and the window function. The horizontal axis in FIG. 10 is the optical path difference x between the first optical path and the second optical path, and the vertical axis is the amplitude. The solid line in FIG. 10 shows the interferogram shape, and the broken line shows the window function.

By operating as described above, the measurement data in the interferogram of the predetermined light is output from the AD conversion unit 26 to the control calculation unit 41, and this measurement data is stored in the sampling data storage unit 411. Then, in order to improve the S / N ratio and obtain a result with good accuracy, the interferogram of such a predetermined light is measured in a similar manner a plurality of times in accordance with the reciprocation of the movable mirror 115, Each measurement data of the interferogram is stored in the sampling data storage unit 411. That is, when the movable mirror 115 reciprocates once, one scan is completed, and one measurement data of the interferogram is obtained.

Next, the integrated interferogram calculation unit 413 obtains an integrated interferogram for the predetermined light by integrating a plurality of interferograms of the predetermined light obtained by measuring a plurality of times while performing alignment. .

Next, the center burst position calculation unit 412 obtains the position of the center burst in the integrated interferogram. And the spectrum calculation part 414 calculates | requires the spectrum of predetermined light by carrying out the Fourier transformation of the integration interferogram calculated | required by the integration interferogram calculation part 413. FIG. Hereinafter, the calculation of this spectrum will be described in more detail.

First, the interferogram F _m at m th measurement _{(x i)} is the optical path difference and x _i, the wave number and [nu _j, the spectral amplitude of the wave number [nu _j and B ([nu _j), the optical path difference 0 When the position is X ₀ and the phase at the position of the optical path difference 0 of the wave number ν _j is φ (ν _j ), it is expressed by Expression 1. Note that m represents the measurement result of the mth measurement.

Therefore, the integrated interferogram F (x _i ) is expressed by Equation 2.

Thus, when the integrated interferogram is obtained by the integrated interferogram calculating unit 413, the spectrum calculating unit 414 obtains a spectrum of predetermined light by, for example, fast Fourier transform (FFT) of the integrated interferogram.

More specifically, in the case of fast Fourier transform, in order to reduce the occurrence of side lobes, a window function A _window (x _i ) that is symmetric about the optical path difference 0 (center burst position) is multiplied. (Expression 3), fast Fourier transform is performed to obtain the amplitude | B _window (ν _j ) | of the spectrum of the predetermined light (Expression 4).

Here, FIG. 11 shows an example of the amplitude | B _window (ν _j ) | of the spectrum of the predetermined light. The horizontal axis in FIG. 11 indicates the wavelength (λ _j ), and the vertical axis indicates the spectral intensity | B _window (ν _j ) |.

The window function A _window (x _i ) can include various appropriate functions. For example, it is a function represented by Formula 5-1 to Formula 5-3. Equation 5-1 is called the Hanning Window function, Equation 5-2 is called the Hamming Window function, and Equation 5-3 is called the Blackman Window function. .

As described above, when the spectrum is obtained, the control calculation unit 41 outputs the obtained spectrum to the output unit 43.

According to the FT spectrometer 10 described above, control of the reciprocating vibration of the movable mirror 115 is controlled using an oscillation signal (self-excited signal) based on the reciprocal vibration of the movable mirror 115 (so-called self-excited driving is performed). ), The reciprocating vibration of the movable mirror 115 can be stabilized against the noise.

That is, in a PLL control (negative feedback circuit) such as a moving mirror driving unit (driving mechanism) of an interferometer in a conventional Fourier transform spectrometer, a reference frequency signal supplied from an oscillator or the like and a reciprocating vibration of the moving mirror Is compared with the detection signal actually detected, and an oscillation signal having a frequency based on this comparison is output from the voltage controlled oscillator to the moving mirror driving unit. For this reason, the Fourier transform spectrometer of the conventional example is easily unlocked when noise is applied to any of the signals (that is, the frequency of the oscillation signal input to the moving mirror driving unit changes), and the moving mirror reciprocates. The vibration cannot be stabilized. However, driving by self-excited oscillation is performed as in the FT spectrometer 10 of the present embodiment (that is, the reciprocating vibration of the moving mirror 115 is controlled based only on the signal that detects the actual reciprocating vibration of the moving mirror 115). As a result, it becomes difficult to be influenced by external noise, and the reciprocating vibration of the movable mirror 115 can be stabilized against the noise.

In the FT spectrometer 10 of the present embodiment, the switching control unit 616 switches the switch elements 614 and 615 to excite the moving mirror drive signal (oscillation signal) input to the parallel movement mechanism 150 (piezoelectric element 155). By performing the control to switch from the signal to the self-excited signal, the FT spectrometer 10 of the present embodiment can reciprocately vibrate from the state where the moving mirror 115 is stationary (stopped) in the interferometer 11. That is, since the reciprocal vibration of the moving mirror 115 cannot be detected by the moving mirror operation detecting unit 200 when the moving mirror 115 is stationary (the detection signal is flat), the self-excited signal generating unit 612 cannot be driven. When the excitation signal from the excitation signal generator 611 is input to the parallel movement mechanism 150, the parallel movement mechanism 150 drives the movable mirror 115, and the movable mirror 115 starts to reciprocate (resonance vibration). When the amplitude of the reciprocating vibration of the movable mirror 115 reaches a predetermined magnitude (in this embodiment, the voltage width (amplitude) of the detection signal is equal to or greater than the hysteresis voltage of the comparator), the movable mirror operation detection unit 200 reciprocates the movable mirror 115. Since the self-excitation signal that can drive the parallel movement mechanism 150 is output from the self-excitation signal generation unit 612 by detecting the vibration, the moving mirror drive signal input to the parallel movement mechanism 150 by the signal switching unit 613 is derived from the excitation signal. By switching to the self-excited signal, driving by self-excited oscillation is performed, and the reciprocating vibration of the movable mirror 115 is hardly affected by external noise.

Next, the second embodiment will be described with reference to FIGS. 12 and 13. The same reference numerals are used for the same components as those in the first embodiment, and the description thereof is omitted. Only different components will be described below. To do. FIG. 12 is a block diagram showing the configuration of the moving mirror drive circuit and the amplitude control circuit of the Fourier transform spectrometer according to the second embodiment. FIG. 13 is a diagram showing how the amplitude of the movable mirror responds when the amplitude target of the movable mirror is changed in the Fourier transform spectrometer. The horizontal axis in FIG. 13 is time, and the vertical axis is the amplitude of the moving mirror. TC is an amplitude target change timing.

In the FT spectrometer of the present embodiment, the configuration of the moving mirror control unit 60A is different from that of the FT spectrometer 10 of the first embodiment. More specifically, the moving mirror control unit 60A of this embodiment includes a moving mirror operation detection unit 200 and a parallel movement mechanism control unit 610A, and the parallel movement mechanism control unit 610A includes an excitation signal generation unit 611. A self-excited signal generation unit 612, a signal switching unit 613, and an amplitude control unit 620.

The amplitude controller 620 includes an amplitude detector 621, an amplitude controller 622, and a mixer 623, and controls the amplitude of the reciprocating vibration of the movable mirror 115 based on the detection result of the movable mirror operation detector 200.

The amplitude detector 621 detects the amplitude of the reciprocating vibration of the movable mirror 115 based on the detection signal output from the movable mirror operation detector 200 and outputs an amplitude signal corresponding to the amplitude signal to the amplitude controller 622. More specifically, the amplitude detector 621 receives the self-excitation signal output from the self-excitation signal generation unit 612 and the zero-cross signal output from the zero-cross detection unit 37, so that the amplitude in the reciprocal vibration of the movable mirror 15 is input. Is detected. The self-excited signal input to the amplitude detector 621 is delayed in phase by 90 ° with respect to the detection signal, but since the frequency is the same as that of the detection signal, the period of the reciprocating vibration of the movable mirror 115 ( One reciprocal movement in the optical axis direction) can be detected. The amplitude detector 621 detects the number of zero crosses in one cycle (or half cycle) of the movable mirror 115 detected from the self-excited signal using the input zero cross signal, and according to the detection result. Output an amplitude signal. That is, the amplitude detector 621 of the present embodiment acquires the detection signal from the moving mirror operation detecting unit 200 as a self-excited signal through the self-excited signal generating unit 612, and the reciprocating of the moving mirror 115 based on this signal. Detect the period of vibration. Then, the amplitude detector 621 simulates the number of zero crossings in one cycle (or half cycle) of the movable mirror 115 with the amplitude in the reciprocating vibration of the movable mirror 115 and outputs it to the amplitude controller 622.

The amplitude detector 621 directly detects the amplitude of the reciprocating vibration of the movable mirror 115 from the detection signal (for example, the amplitude of the detection signal (the vertical width of the voltage)) from the movable mirror operation detection unit 200. Also good.

The amplitude controller 622 outputs an amplitude adjustment signal for adjusting the amplitude (voltage) of the self-excitation signal and the excitation signal based on the input amplitude signal. The amplitude controller 622 of this embodiment is, for example, a PID controller. The amplitude controller 622 can obtain an optical path difference (an optical path difference between the first and second optical paths of the interferometer 11) necessary for obtaining a target half width of a spectrum of predetermined light (for example, the movable mirror 115). The amplitude adjustment signal is output so that the number of zero crossings in one cycle becomes a predetermined value.

The mixer 623 mixes the amplitude adjustment signal output from the amplitude controller 622 with the self-excited signal or excitation signal input to the translation mechanism 150, thereby adjusting the amplitude (voltage) of the self-excited signal or excitation signal. Adjust and output.

Further, the parallel movement mechanism control unit 610A of the present embodiment further includes a D / A control signal generator 617 and a D / A converter 618. The D / A control signal generator 617 creates a control signal (digital signal) for controlling the translation mechanism 150 from the self-excitation signal or the excitation signal whose amplitude is adjusted by the amplitude control unit 620, and the D / A converter Output to 618. The D / A converter 618 converts the control signal (digital signal) from the D / A control signal generator 617 into an analog signal and outputs the analog signal to the parallel movement mechanism 150.

The above FT spectrometer can accurately adjust the amplitude of the reciprocating vibration of the moving mirror 115 (specifically, the moving distance in the optical axis direction). That is, the FT spectrometer of the present embodiment detects the actual amplitude of the movable mirror 115 when the amplitude magnitude (amplitude target) of the target movable mirror 115 is changed, and based on this detection result. Since the amplitude of the movable mirror 115 can be adjusted, as shown in FIG. 13, the amplitude of the movable mirror 115 after changing the magnitude of the amplitude can be accurately matched with the amplitude target. In the FT spectrometer of the present embodiment, the actual amplitude of the movable mirror 115 is detected and the amplitude of the movable mirror 115 is adjusted based on the detection result. Therefore, the FT spectrometer of the present embodiment is The reciprocating vibration of the movable mirror 115 can be made constant, that is, the maximum value and the minimum value of the optical path difference generated between the two optical paths that guide the predetermined light in the interferometer 11 can be made constant. The spectrum of the predetermined light can be measured with higher accuracy.

Next, the third embodiment will be described with reference to FIGS. 14 to 20, but the same reference numerals are used for the same components as those of the first and second embodiments, the description thereof is omitted, and only different components will be described below. Explained.

FIG. 14 is a block diagram showing a configuration of a moving mirror driving circuit and an amplitude control circuit of a Fourier transform spectrometer according to the third embodiment. FIG. 15 is a circuit diagram showing a configuration of a low-pass filter (IIR filter) that constitutes a self-excited signal generator of the Fourier transform spectrometer. FIG. 16 is a diagram illustrating the characteristics of the low-pass filter, FIG. 16A illustrates the frequency characteristics, and FIG. 16B illustrates the phase characteristics. FIG. 17 is a diagram illustrating an example of a square-wave detection signal and an output waveform of the low-pass filter when the detection signal is input to the low-pass filter. FIG. 17A illustrates an example of a square-wave detection signal, and FIG. 17B is a diagram illustrating an output waveform of the low-pass filter when the detection signal illustrated in FIG. 17A is input to the low-pass filter. The horizontal axis of FIG. 17A and FIG. 17B is time, and each of those vertical axes is amplitude. FIG. 18 is a diagram illustrating an example of a detection signal on which noise is superimposed and the detection signal converted into a square wave signal by passing through a comparator. In FIG. 18, the upper graph is the detection signal SG4 output from the photoreflector, and the lower graph is the detection signal SG5 that has been converted to a square wave signal by passing through a comparator. The horizontal axis in FIG. 18 is time, and the vertical axis is voltage.

The FT spectrometer of the present embodiment is different from the FT spectrometer of the second embodiment in the configuration of the self-excited signal generator 612B in the moving mirror controller 60B. More specifically, the moving mirror control unit 60B includes a moving mirror operation detection unit 200 and a parallel movement mechanism control unit 610B. The parallel movement mechanism control unit 610B includes an excitation signal generation unit 611 and a low-pass filter 612B. A signal switching unit 613 and an amplitude control unit 620.

The low-pass filter 612B of the present embodiment has a phase with respect to the reciprocal vibration of the movable mirror 115 detected by the movable mirror operation detection unit 200 when the second switch element 615 is turned on and the first switch element 614 is turned off. Outputs a sine wave self-excited signal delayed by 90 °. In the present embodiment, this low-pass filter 612B constitutes a self-excited signal generator. The low-pass filter 612B is a digital low-pass filter such as an IIR filter (Infinite Impulse Response Filter: Infinite Impulse Response Filter) or an FIR filter (Finite Impulse Response Filter: Finite Impulse Response Filter). In the present embodiment, for example, It is an IIR filter as shown in FIG. The IIR filter (self-excited signal generator) 612B is a circuit including a feedback path and a forward path, which is configured by an amplifier, a subtracter, an adder, and a delay element. More specifically, the IIR filter 612B of the present embodiment includes four amplifiers (first to fourth amplifiers 6001 to 6004), two subtracters (first and second subtractors 6011 and 6012), 2 There are two adders (first and second adders 6021 and 6022) and two delay elements (first and second delay elements 6031 to 6032). In the IIR filter 612B, the first amplifier 6001 amplifies the input signal (detection signal) from the movable mirror operation detection unit 200 at a predetermined magnification, and first subtracts the amplified signal (first amplification signal). Output to the device 6011. The first amplified signal output from the first amplifier 6001 and the second amplified signal output from the second amplifier 6002 are input to the first subtractor 6011, and the first subtractor 6011 outputs the input signals. The first difference signal that is the difference is output to the second subtractor 6012. The first differential signal output from the first subtractor 6011 and the fourth amplified signal output from the fourth amplifier 6004 are input to the second subtractor 6012, and the second subtractor 6012 receives the input signals. The second difference signal that is the difference is output to the first delay element 6031 and the first adder 6021. The first delay element 6031 delays the second differential signal output from the second subtractor 6012 by one cycle (one clock), and the delayed signal (first delay signal) is sent to the second amplifier 6002 and the second amplifier 6002. To the second delay element 6032 and the third amplifier 6003. The second amplifier 6002 amplifies the first delayed signal output from the first delay element by a predetermined magnification, and outputs the amplified signal (second amplified signal) to the first subtractor 6011. The second delay element 6032 further delays the first delay signal output from the first delay element 6031 by one period (one clock), and the delayed signal (second delay signal) is the fourth amplifier 6004. And output to the second adder 6022. The third amplifier 6003 amplifies the first delayed signal output from the first delay element 6031 by a predetermined magnification, and outputs the amplified signal (third amplified signal) to the first adder 6021. In addition, the second difference signal output from the second subtractor 6012 and the third amplified signal output from the third amplifier 6003 are input to the first adder 6021, and the first adder 6021 receives these inputs. The first sum signal, which is the sum of the received signals, is output to the second adder 6022. The first sum signal output from the first adder 6021 and the second delay signal output from the second delay element 6032 are input to the second adder 6022, and the second adder 6022 receives these inputs. The second sum signal, which is the sum of the signals, is output to the mixer 623 connected to the output side of the IIR filter 612B.

As shown in FIGS. 16A and 16B, this IIR filter (self-excited signal generator) 612B has a characteristic that the phase is delayed by 90 ° at the resonance frequency f ₀ (70 Hz in the present embodiment) of the parallel movement mechanism 150. Yes.

This self-excited signal generation unit 612B receives a detection signal (square wave signal: see FIG. 17A) from the moving mirror operation detection unit 200, and sine wave oscillation whose phase is delayed by 90 ° with respect to the detection signal. A signal (see FIG. 17B) is output.

The low-pass filter 612B of this embodiment also has a function as a sine wave generator by being disposed between the excitation signal generator 611 and the D / A control signal generator 617. That is, the low-pass filter 612B according to the present embodiment converts the excitation signal (square wave oscillation signal) output from the excitation signal generation unit 611 into a sine wave oscillation signal (excitation signal) to generate a D / A control signal generator. To 617.

Thus, in the FT spectrometer of this embodiment, since both the self-excitation signal and the excitation signal input to the translation mechanism 150 are sinusoidal oscillation signals, the FT spectrometer of this embodiment The oscillation due to the higher-order resonance mode of the translation mechanism 150 that occurs when a square-wave oscillation signal is input to the translation mechanism 150 can be prevented.

In the FT spectrometer of the present embodiment, the low-pass filter 612B is configured by a digital low-pass filter. Therefore, the FT spectrometer of the present embodiment has a filter characteristic that is caused by variations in circuit constants such as an analog low-pass filter. Variations can be prevented from occurring. By configuring the low-pass filter 612B with a digital low-pass filter, no external IC is required, and the FT spectrometer of this embodiment can reduce the size of the filter circuit.

As shown in FIG. 18, even if noise is superimposed on the detection signal output from the moving mirror operation detection unit (photoreflector) 200, the low-pass filter 612B is a high-frequency filter in the FT spectrometer of this embodiment. In order to cut noise, the FT spectrometer of this embodiment can suppress the noise of the self-excited signal after passing through the low-pass filter 612B.

When the moving mirror operation detection unit 200 includes a photo reflector as in the FT spectrometer of the present embodiment, when the photo reflector is installed in the interferometer 11 by configuring the self-excited signal generation unit with the low-pass filter 612B. Even if the positioning accuracy is low, the influence on the measurement accuracy of the spectrum of the predetermined light can be suppressed. Details are as follows. FIG. 19 is a diagram illustrating the relationship between the distance from the photo reflector to the measurement target and the output voltage from the photo reflector. The horizontal axis in FIG. 19 is the distance from the photo reflector to the measurement object, and the vertical axis is the output of the photo reflector. FIG. 20 is a non-linear region in the relationship between the distance to the measurement object and the output voltage, and the detection signal obtained from the output of the photoreflector when the reciprocal vibration of one end of the translation mechanism is measured by the photoreflector, and this It is a figure which shows the output signal of the said low-pass filter when a detection signal is input into a low-pass filter. FIG. 20A is obtained from the output of the photoreflector when the reciprocal vibration of one end of the translation mechanism is measured by the photoreflector in a region that is not a linear region in the diagram showing the relationship between the distance to the measurement target and the output voltage. FIG. 20B is a diagram illustrating an output signal of the low-pass filter when the detection signal of FIG. 20A is input to the low-pass filter. The horizontal axis in FIGS. 20A and 20B is time, and the vertical axis thereof is amplitude.

The amplitude of the movable mirror 115 (specifically, the change in the distance from the photo reflector to the back surface (measurement target) of one end of the parallel movement mechanism 150) is detected in the range (linear region) with good linearity in FIG. In addition, when a photo reflector is arranged (positioned) in the interferometer 11, a detection signal having a duty ratio of 50% is obtained from the photo reflector. However, the photoreflector is arranged in the interferometer 11 so as to be detected in a range with poor linearity in FIG. 19 (for example, a range in which the peak position of the graph shown in FIG. 19 is included, that is, a region that is not a linear region). Then, only a detection signal having a duty ratio smaller than 50% can be obtained from this photo reflector.

As described above, when the duty ratio of the detection signal is smaller than 50%, a sufficiently large amplitude cannot be obtained in the reciprocating vibration of the movable mirror 115, thereby reducing the measurement accuracy in measuring the spectrum of the predetermined light. However, a detection signal with a small duty ratio (for example, a detection signal with a duty ratio of 30%: see FIG. 20A) is passed through the low-pass filter (self-excited signal generation unit) 612B of the present embodiment to be third order or higher. By cutting the higher harmonics, a sinusoidal signal (self-excited signal) with a duty ratio of 50% is obtained (see FIG. 20B). For this reason, in the FT spectrometer of the present embodiment, even if the arrangement position of the photo reflector is a position where the amplitude of the movable mirror 115 is detected in the range with poor linearity (nonlinear region) in FIG. Self-excited signal having a duty ratio of 50% (that is, an oscillation signal (moving mirror drive signal) whose phase is delayed by 90 ° with respect to the detection signal input to low-pass filter 612B) is input to translation mechanism 150. For this reason, the measurement accuracy of the spectrum of the predetermined light does not decrease.

In the FT spectrometer according to the present embodiment, the sine wave generator and the self-excited signal generator arranged between the excitation signal generator 611 and the D / A control signal generator 617 have a common low-pass filter 612B. In other words, the self-excitation signal generation unit also serves as a sine wave generation unit that converts a square-wave excitation signal into a sine-wave excitation signal, but is not limited to this configuration. For example, the sine wave generator and the self-excited signal generator disposed between the excitation signal generator 611 and the D / A control signal generator 617 may be configured by different low-pass filters.

Next, the fourth embodiment will be described with reference to FIG. 21 and FIG. 22. The same reference numerals are used for the same components as those in the first to third embodiments, the description is omitted, and only different components are described below. Explained.

FIG. 21 is a block diagram showing the configuration of the resonance frequency detection circuit of the parallel movement mechanism. FIG. 22 shows an example of a photoreflector detection signal when the amplitude of the moving mirror is observed while changing the frequency of the moving mirror drive signal that is an oscillation signal input to the parallel movement mechanism, and when this detection signal is input. It is a figure which shows the output signal of this comparator. In FIG. 22, the upper graph is the photoreflector detection signal SG6, and the lower graph is the comparator output signal SG7. In addition, the horizontal axis of FIG. 22 is frequency, and the vertical axis is voltage.

The FT spectrometer of the present embodiment is different from the FT spectrometers of the first to third embodiments in the configuration of the excitation signal generator 611C and the control calculator 41C. The excitation signal generation unit 611C and the control calculation unit 41C generate an excitation signal (specifically, the parallel movement mechanism 150 in a stationary state based on the detection result by the moving mirror operation detection unit 200 when the oscillation signal is output while changing the frequency). The frequency of the oscillation signal output from the excitation signal generation unit 611C in order to start the reciprocating vibration is determined.

The excitation signal generator 611C of this embodiment can change the frequency of the oscillation signal to be output. The control calculation unit 41C further includes a storage unit (storage area) 415 and an excitation frequency determination unit 416. The storage unit 415 stores the detection signal input from the movable mirror operation detection unit 200 and the frequency of the oscillation signal output from the excitation signal generation unit 611C in association with each other. The excitation frequency determining unit 416 uses the frequency f ₁ (see FIG. 22) of the oscillation signal when the amplitude (the vertical width of the voltage in the detection signal) is maximum in the detection signal as the resonance frequency at which resonance vibration occurs in the translation mechanism 150. f is ₀ and fiction, to output the oscillation signal of the frequency f ₁ as the excitation signal to the excitation signal generator 611C.

More specifically, in the FT spectrometer of the present embodiment, the movable mirror 115 is moved by the parallel movement mechanism 150 while changing the frequency of the oscillation signal output from the excitation signal generator 611C at intervals of Δf from the frequency f _min to f _max. The excitation frequency determination unit 416 monitors the amplitude of the movable mirror 115 based on the detection signal from the movable mirror operation detection unit 200 input during this period. Then, the excitation frequency determination unit 416 extracts the frequency f ₁ of the oscillation signal when the amplitude of the movable mirror 115 becomes the maximum in the detection signal from the storage unit 415, and uses this frequency f ₁ as the resonance frequency f ₀ (see FIG. 22). In the example shown, 72 Hz), the excitation signal generator 611C outputs the oscillation signal of this frequency f1 as an excitation signal. Even if the frequency input to the parallel movement mechanism 150 is slightly deviated from the resonance frequency f ₀ , this deviation is within the range in which the vibration of the movable mirror in FIG. 22 is detected (for example, the frequencies f ₂ to f in FIG. 22). ₃ ), the translation mechanism 150 starts to vibrate.

The above FT spectrometer can reliably reciprocate the movable mirror 115 from the stationary state in the interferometer 11. That is, the FT spectrometer of the present embodiment, for example, when the frequency of the excitation signal deviates from the value set in the excitation signal generator 611, or when the value is not set in advance, The frequency of the oscillation signal is scanned to obtain the frequency when the reciprocal vibration of the movable mirror 115 is detected, and the oscillation signal (excitation signal) of this frequency is output to the parallel movement mechanism 150, whereby the interferometer 11 performs the movable mirror 115 can be reliably reciprocated from a stationary state.

Note that the excitation frequency determination unit 416 of the present embodiment uses the frequency f _{1 of the} oscillation signal output from the excitation signal generation unit 611C when the amplitude of the movable mirror 115 is maximized in the input detection signal as the resonance frequency f _0. However, it is not limited to this configuration. For example, when the excitation frequency determination unit 416 converts the detection signal into a square wave signal through a hysteresis control comparator, the frequency range f ₂ to f ₃ in which the vibration of the movable mirror 115 is detected in the square wave signal. The configuration may be such that the center frequency f ₄ (see the lower graph in FIG. 22) is simulated as the resonance frequency f ₀ and the excitation signal generator 611C outputs the oscillation signal of the frequency f ₄ as the excitation signal.

In the above-described Fourier transform spectrometer, the parallel movement mechanism 150 is used as an example of the moving mirror driving unit, but the moving mirror driving unit is not limited to this. For example, in the configuration shown in FIG. 3, the movable mirror driving unit includes a magnet unit provided on the first support 153, and a coil unit disposed away from the magnet unit so as to face the magnet unit. May be provided instead of the piezoelectric element 155. The coil portion is disposed at a position that does not interfere with the movement ranges of the first leaf spring 151, the second leaf spring 152, and the movable mirror 115 (a position that does not hinder each movement). The first support 153 alternately applies force upward and downward due to the interaction between the magnetic field generated in the coil part by applying an AC voltage to the coil part and the magnetic field of the magnet part. Receiving and resonance driving. When this AC voltage is applied, the coil unit is controlled by the parallel movement mechanism control unit 610 using a self-excited signal that is an oscillation signal based on the detection result of the moving mirror operation detection unit 200.

This specification discloses various modes of technology as described above, and the main technologies are summarized below.

A Fourier transform spectrometer according to one aspect is a Fourier transform spectrometer that obtains a spectrum of the predetermined light by performing a Fourier transform on an interferogram of the predetermined light, and includes a distance from an incident position of the predetermined light to an interference position. A plurality of optical elements that form two optical paths between them, and a movable mirror included in the plurality of optical elements based on an input oscillation signal are reciprocally oscillated in the direction of the optical axis. A self-excited signal that is an oscillation signal based on a detection result of the moving mirror operation detecting unit, a moving mirror operation detecting unit that detects reciprocal vibration of the moving mirror, A self-excited signal generating unit that outputs a signal to the movable mirror driving unit.

Such a Fourier transform spectrometer controls the reciprocating vibration of the moving mirror using an oscillation signal (self-excited signal) based on the reciprocating vibration (reciprocating movement) of the moving mirror (so-called self-excited oscillation is performed). Therefore, it is difficult to be affected by external noise, so that the reciprocating vibration of the movable mirror can be stabilized against the noise.

That is, in a PLL control (negative feedback circuit) such as a moving mirror driving unit (driving mechanism) of an interferometer in a conventional Fourier transform spectrometer, a reference frequency signal supplied from an oscillator or the like and a reciprocating vibration of the moving mirror are generated. The actually detected detection signal is compared, and an oscillation signal having a frequency based on this comparison is output from the voltage controlled oscillator to the moving mirror driving unit. For this reason, the conventional Fourier transform spectrometer is easily unlocked when noise is applied to any signal (that is, the frequency of the oscillation signal input to the moving mirror drive unit changes), and the reciprocating vibration of the moving mirror Cannot be stabilized. However, the Fourier transform spectrometer having the above-described configuration is driven by self-excited oscillation (that is, the reciprocating vibration of the moving mirror is controlled based on the signal that detects the actual reciprocating vibration of the moving mirror). The reciprocal vibration of the movable mirror can be stabilized against the noise.

In another aspect, in the above-described Fourier transform spectrometer, the moving mirror driving unit that drives the moving mirror of the interferometer includes a parallel moving mechanism including a pair of leaf spring members arranged in parallel so as to face each other. A leaf spring driving unit that vibrates the leaf spring member based on the input oscillation signal, and the movable mirror is reciprocally vibrated in the optical axis direction by the vibration of the pair of leaf spring members.

The Fourier transform spectrometer preferably has an excitation signal generator that outputs an excitation signal, which is an oscillation signal based on a resonance frequency at which the pair of leaf spring members resonate, to the movable mirror drive unit; You may further provide the signal switching part which switches the oscillation signal input into a moving mirror drive part between the self-excitation signal from the said self-excitation signal generation part, and the excitation signal from the said excitation signal generation part.

In such a Fourier transform spectrometer, the movable mirror can reciprocate from a stationary state in the interferometer. That is, the Fourier transform spectrometer cannot be driven by self-excited oscillation because the moving mirror operation detector cannot detect the reciprocal vibration of the moving mirror when the moving mirror is stationary (ie, the moving mirror drive from the signal generator). However, when the excitation signal from the excitation signal generation unit is input to the moving mirror driving unit, the moving mirror driving unit drives the moving mirror and starts reciprocating vibration. When the movable mirror starts to reciprocate, the movable mirror operation detector detects the reciprocal vibration of the movable mirror and outputs a self-excited signal that can drive the movable mirror driver from the self-excited signal generator. By switching the oscillation signal input to the moving mirror driving unit from the excitation signal to the self-excited signal by the switching unit, driving by self-excited oscillation is performed. As a result, the reciprocating vibration of the moving mirror is affected by external noise. It becomes difficult.

In this case, it is preferable that the signal switching unit generates an oscillation signal to be output to the moving mirror driving unit from the excitation signal when the moving mirror operation detecting unit detects reciprocal vibration of the moving mirror. Switch to excitation signal. As a result, the Fourier transform spectrometer can be automatically switched to drive by self-excited oscillation after reciprocating vibration from the stopped state using the excitation signal.

In the above case, preferably, the signal switching unit switches the oscillation signal to be output from the excitation signal to the self-excitation signal after outputting the excitation signal to the movable mirror driving unit for a predetermined time, for example. As a result, the Fourier transform spectrometer can automatically switch to driving by self-excited oscillation after reciprocatingly vibrating the movable mirror from a stationary state using an excitation signal. That is, according to the above-described configuration, when the excitation signal is input to the movable mirror driving unit for a predetermined time, the movable mirror starts reciprocating vibration from a stopped state, and thereafter (after the predetermined time elapses), driving by self-excited oscillation Control to switch to is performed.

In another aspect, in the above-described Fourier transform spectrometer, the excitation signal generation unit outputs the excitation signal based on a detection result by the moving mirror operation detection unit when an oscillation signal is output while changing the frequency. decide. As a result, such a Fourier transform spectrometer can reliably reciprocate the moving mirror from the stationary state in the interferometer. That is, for example, even when the frequency of the excitation signal deviates from the value set in the excitation signal generator, or when the value is not set in advance, such a Fourier transform spectrometer can oscillate. The frequency of the signal is swept (scanned) to obtain the frequency when the reciprocating vibration of the moving mirror is detected, and the oscillation signal (excitation signal) of the obtained frequency is output to the moving mirror driving unit, so that the interferometer The movable mirror can be reliably reciprocated from a stationary state.

In another aspect, in the above-described Fourier transform spectrometer, preferably, the moving mirror driving unit vibrates the pair of leaf spring members with a driving force according to an amplitude of an input oscillation signal, The self-excited signal generator outputs an oscillation signal whose phase is delayed by 90 ° with respect to the reciprocating vibration of the movable mirror detected by the movable mirror operation detector.

In such a Fourier transform spectrometer, the driving force to the moving mirror becomes zero when the moving mirror is at one end or the other end position in the vibration direction (see Xm and -Xm in FIG. 4B) in the reciprocating vibration of the moving mirror. The largest driving force is applied in the moving direction when the moving mirror is at an intermediate position (position where the moving speed is the highest: see origin position X0 in FIG. 4B) from one end (the other end) to the other end (the one end) in the vibration direction. . For this reason, such a Fourier transform spectrometer can keep the amplitude (the displacement amount in the optical axis direction) of the movable mirror large.

In another aspect, in the above-described Fourier transform spectrometer, preferably, the moving mirror driving unit vibrates the pair of leaf spring members with a driving force according to an amplitude of an input oscillation signal, The self-excited signal generation unit may include a low-pass filter that outputs a sinusoidal self-excited signal that is detected by the moving mirror operation detecting unit and whose phase is delayed by 90 ° with respect to the reciprocating vibration of the moving mirror.

Such a Fourier transform spectrometer prevents oscillation due to the higher-order resonance mode of the moving mirror drive unit that occurs in the case of a square wave (rectangular wave) self-excited signal, and also detects the detection result from the moving mirror operation detection unit ( Even if noise is present on the detection signal), this noise can be reduced by the low-pass filter to suppress the influence of the noise on the spectrum measurement result.

In this case, the low-pass filter is preferably a digital low-pass filter. Such a Fourier transform spectrometer can prevent the occurrence of variations in filter characteristics due to variations in circuit constants, such as an analog low-pass filter, by using a digital low-pass filter.

In another aspect, the above-described Fourier transform spectrometer may further include an amplitude control unit that controls the amplitude of the reciprocating vibration of the movable mirror based on the detection result of the movable mirror operation detection unit.

Such a Fourier transform spectrometer can accurately adjust the amplitude of the reciprocating vibration of the moving mirror (specifically, the moving distance in the optical axis direction). That is, such a Fourier transform spectrometer detects the actual amplitude of the moving mirror when the amplitude magnitude (amplitude target) of the target moving mirror is changed, and based on the detection result, the moving mirror Therefore, the amplitude of the movable mirror after changing the amplitude can be accurately matched with the amplitude target. In addition, according to the above-described configuration, the Fourier transform spectrometer detects the actual amplitude of the moving mirror and adjusts the amplitude of the moving mirror based on the detection result. The amplitude can be made constant, that is, the maximum value and the minimum value of the optical path difference generated between the two optical paths that guide the predetermined light in the interferometer can be made constant, whereby the spectrum of the predetermined light can be measured more accurately. .

This application is based on Japanese Patent Application No. 2013-7212 filed on January 18, 2013, the contents of which are included in the present application.

In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

According to the present invention, a Fourier transform spectrometer can be provided.

Claims (10)

1. A Fourier transform spectrometer that obtains a spectrum of the predetermined light by Fourier transforming an interferogram of the predetermined light,
   A plurality of optical elements that form two optical paths between the incident position of the predetermined light and the interference position, and a movable mirror included in the plurality of optical elements based on an input oscillation signal in the optical axis direction An interferometer having a moving mirror driving unit that causes a difference in optical path between the two optical paths by reciprocating vibration;
   A movable mirror operation detector for detecting reciprocal vibration of the movable mirror;
   A self-excited signal generating unit that outputs a self-excited signal that is an oscillation signal based on a detection result of the moving mirror operation detecting unit to the moving mirror driving unit,
   Fourier transform spectrometer.
2. The moving mirror driving unit is
   A parallel movement mechanism comprising a pair of leaf spring members arranged in parallel to face each other;
   A leaf spring drive unit that vibrates the leaf spring member based on the input oscillation signal,
   Reciprocally vibrate the movable mirror in the optical axis direction by vibration of the pair of leaf spring members;
   The Fourier transform spectrometer according to claim 1.
3. An excitation signal generating unit that outputs an excitation signal, which is an oscillation signal based on a resonance frequency at which the pair of leaf spring members resonate, to the movable mirror driving unit;
   A signal switching unit that switches an oscillation signal input to the movable mirror driving unit between a self-excitation signal from the self-excitation signal generation unit and an excitation signal from the excitation signal generation unit;
   The Fourier transform spectrometer according to claim 2.
4. The signal switching unit switches the oscillation signal output to the moving mirror driving unit from the excitation signal to the self-excited signal when the moving mirror operation detecting unit detects reciprocal vibration of the moving mirror.
   The Fourier transform spectrometer according to claim 3.
5. The signal switching unit switches the oscillation signal to be output from the excitation signal to the self-excitation signal after outputting the excitation signal to the movable mirror driving unit for a predetermined time.
   The Fourier transform spectrometer according to claim 3.
6. The excitation signal generation unit determines the excitation signal based on a detection result by the moving mirror operation detection unit when an oscillation signal is output while changing a frequency.
   The Fourier transform spectrometer according to any one of claims 3 to 5.
7. The movable mirror driving unit vibrates the pair of leaf spring members with a driving force according to the amplitude of an input oscillation signal,
   The self-excited signal generator outputs an oscillation signal whose phase is delayed by 90 ° with respect to the reciprocal vibration of the movable mirror detected by the movable mirror operation detector.
   The Fourier transform spectrometer according to any one of claims 2 to 6.
8. The movable mirror driving unit vibrates the pair of leaf spring members with a driving force according to the amplitude of an input oscillation signal,
   The self-excited signal generator has a low-pass filter that outputs a sinusoidal self-excited signal that is detected by the movable mirror operation detector and is delayed in phase by 90 ° with respect to the reciprocating vibration of the movable mirror.
   The Fourier transform spectrometer according to any one of claims 2 to 6.
9. The low pass filter is a digital low pass filter.
   The Fourier transform spectrometer according to claim 8.
10. An amplitude controller that controls the amplitude of the reciprocating vibration of the movable mirror based on the detection result of the movable mirror operation detector;
    The Fourier transform spectrometer according to any one of claims 1 to 9.

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