JP5891955B2 - Timing generation apparatus for Fourier transform spectrometer and method, Fourier transform spectrometer and method - Google Patents

Description

  The present invention uses a timing generation apparatus for a Fourier transform spectrometer, a timing generation method for a Fourier transform spectrometer, and a timing generation apparatus for the Fourier transform spectrometer, which are preferably used for a Fourier transform spectrometer, and the generation method. The present invention relates to a Fourier transform spectrometer and a Fourier transform spectroscopic method.

  A spectrometer is a device that measures a spectrum that represents a component (light intensity) of each wavelength (each wave number) in light to be measured, one of which is measuring the interference light of the light to be measured with an interferometer, There is a Fourier transform spectrometer that obtains the spectrum of light to be measured by Fourier transforming the measurement result.

  In this Fourier transform type spectrometer, the output of the interferometer is interference light of the measured light that interferes while changing the optical path difference, and light of a plurality of wavelengths included in the measured light is transmitted by the interferometer. This is a combined waveform that is interfered at once, and is called an interferogram. Then, the spectrum of the light to be measured is obtained by Fourier transforming the interferogram. More specifically, the Fourier transform spectrometer photoelectrically converts the interference light of the light to be measured output from the interferometer, and samples an electrical signal generated by the photoelectric conversion at a predetermined sampling timing. Thus, the measurement data of the interferogram is obtained, and the measurement data of the interferogram is Fourier transformed to obtain the spectrum of the light to be measured. 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, and the center peak of the one or more steep peaks has a center burst. Called.

  In such a Fourier transform spectrometer, when the predetermined sampling timing deviates from a desired timing, a false spectrum that is not the spectrum of the light to be measured is generated in the spectrum of the light to be measured that is finally obtained.

  Therefore, for example, Patent Document 1 and Patent Document 2 disclose techniques for avoiding such generation of a false spectrum. The data processing method of the Fourier transform spectrometer disclosed in Patent Document 1 is a sample hold signal obtained by incorporating a laser interferometer for optical path difference measurement into a Fourier transform spectrometer and binarizing the laser interference signal of the laser interferometer. Is a data processing method of a Fourier transform spectrometer that samples the interference signal output from the photodetector and analyzes the spectrum of the sampled interference signal at 1 / n wavelength intervals of the laser interference signal. The interference signal is sampled, and the sampled interference signal is separated into n pieces of data every n pieces and subjected to Fourier transform, and then each data is added. More specifically, in this data processing method, sampling is performed at the rising timing and falling timing of the laser interference signal, and the data of only the rising timing and the data of only the falling timing are treated independently and Fourier transformed. Each data is added.

  Further, the interference spectrophotometer disclosed in Patent Document 2 introduces laser light emitted from a laser light source and infrared light emitted from an infrared light source into the same interferometer to generate interference light. In the interference spectrophotometer for determining the timing for sampling the received light signal of the infrared interference light based on the phase inversion means for generating a reverse phase signal obtained by inverting the polarity of the interference fringe signal of the laser interference light, and the interference fringe signal Two amplitude comparison means for comparing the amplitudes of the positive phase signal and the negative phase signal with the same reference voltage and converting them to a binary signal, and either the rising edge or the falling edge of the output signal of the amplitude comparison means Two edge detection means for detecting one of them and generating a pulse signal corresponding thereto, and two systems of pulse signals from the edge detection means, the received light signal of the infrared interference light is respectively sampled. And a, and two sampling means for the ring.

JP-A-2-27226 JP 2000-2589 A

  Incidentally, the data processing method disclosed in Patent Document 1 can reduce the generation of the false spectrum. However, in the data processing method disclosed in Patent Document 1, since n pieces of data are handled independently, the sampling interval of each data becomes n times and it is difficult to measure the spectrum on the short wavelength side. More specifically, in the data of only the rising timing, the sampling interval is doubled compared to the case where both the rising timing and the falling timing are used. Similarly, in the data of only the falling timing, the sampling interval is doubled. The interval is doubled compared to when both the rising timing and falling timing are used.

  Further, in the interference spectrophotometer disclosed in Patent Document 2, since the positive phase signal and the negative phase signal are generated as described above, the amplitude center of the positive phase signal and the amplitude center of the negative phase signal are shifted. Eventually, the sampling timing does not become equal, and there is a possibility that a false spectrum is generated.

  The present invention is an invention made in view of the above-described circumstances, and its purpose is to propose a new method, and a timing generation device for a Fourier transform spectrometer capable of reducing generation of a false spectrum. And providing a timing generation method for a Fourier transform spectrometer. An object of the present invention is to provide a Fourier transform spectrometer timing generation apparatus and a Fourier transform spectrometer and a Fourier transform spectroscopy method using the generation method.

As a result of various studies, the present inventor has found that the above object is achieved by the present invention described below. That is, the Fourier transform spectrometer timing generation device according to one aspect of the present invention samples a signal obtained by photoelectrically converting the interference light of the light to be measured generated by the interferometer at a predetermined sampling timing. Thus, a plurality of measurement data is obtained and used in a Fourier transform spectrometer that obtains the spectrum of the light to be measured using Fourier transform based on the interferogram of the light to be measured by the obtained plurality of measurement data. In the timing generation apparatus for a Fourier transform spectrometer for generating the sampling timing, a light source that emits monochromatic light, a light receiving unit that photoelectrically converts the interference light of the monochromatic light generated by the interferometer, and a reference A reference voltage generating unit that generates a voltage, and an output of the light receiving unit intersects the reference voltage of the reference voltage generating unit. A zero-cross detection unit that outputs a zero cross signal as the sampling timing at a timing, by adjusting the reference voltage of the reference voltage generating unit, in the plurality of measurement data, the optical path difference between two adjacent measurement data with each other And an adjustment unit that adjusts the sampling timing so that they are equal to each other, the adjustment unit from the sampling timing adjustment spectrum obtained when the light having a known wavelength is the light to be measured, In the measurement data, the reference voltage of the reference voltage generation unit is set such that a false spectrum component based on the light caused by non-uniformity in optical path difference between two adjacent measurement data is lost. By adjusting, two adjacent measurements in the plurality of measurement data Such that the optical path difference between the over data are equal to each other, characterized that you adjust the sampling timing.

  The timing generator for a Fourier transform spectrometer having such a configuration includes an adjustment unit that adjusts the sampling timing so that optical path differences between two adjacent measurement data are equal to each other in the plurality of measurement data Therefore, generation of a false spectrum can be reduced.

  The Fourier transform spectrometer timing generation device having such a configuration can reduce the generation of a false spectrum with a relatively simple configuration of adjusting the reference voltage of the zero-cross detection unit.

  The timing generation device for a Fourier transform spectrometer having such a configuration can reduce generation of a false spectrum with a relatively simple configuration of monitoring a spectrum obtained by the Fourier transform spectrometer.

In another aspect, in the above-described Fourier transform spectrometer timing generation device, the adjustment unit determines whether the false spectrum component is included in the sampling timing adjustment spectrum, and the determination As a result, if the false spectral component is included, the current reference voltage is adjusted. If the determination result shows that the false spectral component is not included, the current reference voltage is maintained. Then, by adjusting the reference voltage of the reference voltage generation unit so that the pseudo spectrum component disappears from the sampling timing adjustment spectrum, between the two measurement data adjacent to each other in the plurality of measurement data of so that the optical path difference equal to each other, characterized that you adjust the sampling timing.

In addition, in the timing generation method for a Fourier transform spectrometer according to another aspect of the present invention, a signal obtained by photoelectrically converting the interference light of the light to be measured generated by the interferometer is obtained at a predetermined sampling timing. A Fourier transform spectrometer that obtains a plurality of measurement data by sampling and obtains a spectrum of the light to be measured using a Fourier transform based on an interferogram of the light to be measured based on the obtained plurality of measurement data. In the timing generation method for a Fourier transform spectrometer used to generate the sampling timing, a monochromatic light emitting step for emitting monochromatic light and photoelectrically converting the interference light of the monochromatic light generated by the interferometer A light receiving step, a reference voltage generating step for generating a reference voltage, and an output of the light receiving step before the reference voltage generating step. By adjusting the reference voltage in the reference voltage generation step and a zero-cross detection step of outputting a zero-cross signal as the sampling timing at a timing crossing a reference voltage, two measurements adjacent to each other in the plurality of measurement data An adjustment step for adjusting the sampling timing so that optical path differences between data are equal to each other, and the adjustment step is a sampling timing adjustment spectrum obtained when light having a known wavelength is used as the light to be measured. From the reference voltage generation step, the spurious spectral component based on the light caused by non-uniformity in optical path difference between two adjacent measurement data in the plurality of measurement data is lost. By adjusting the reference voltage of the plurality of measurement data. , So that the optical path difference between two adjacent measurement data are equal to each other to each other, and adjusting the sampling timing.

The Fourier transform spectrometer timing generation method having such a configuration includes an adjustment step of adjusting the sampling timing so that optical path differences between two adjacent measurement data are equal to each other in the plurality of measurement data Therefore, generation of a false spectrum can be reduced. The timing generation method for a Fourier transform spectrometer having such a configuration can reduce the generation of a false spectrum with a relatively simple configuration of adjusting the reference voltage in the zero cross detection step . The timing generation method for a Fourier transform spectrometer having such a configuration can reduce the generation of a false spectrum with a relatively simple configuration of monitoring the spectrum obtained by the Fourier transform spectrometer .

  The Fourier transform spectrometer according to another aspect of the present invention includes a plurality of optical elements that receive predetermined light and form two optical paths between the incident position of the predetermined light and the interference position. The plurality of optical elements includes an interferometer including 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, and a measurement target generated by the interferometer A light receiving unit that photoelectrically converts interference light of light, a sampling unit that obtains a plurality of measurement data by sampling the output of the light receiving unit at a predetermined sampling timing, and the plurality of measurement data obtained by the sampling unit A spectrum calculation unit that obtains a spectrum of the light to be measured using Fourier transform based on an interferogram of the light to be measured, and a table that generates the sampling timing. And a timing generation unit, the timing generation unit may be any timing generator thereof above.

  Since the Fourier transform spectrometer having such a configuration uses any of the above-described timing generation devices, generation of a false spectrum can be reduced.

The Fourier transform type spectroscopic method according to another aspect of the present invention includes a plurality of optical elements that form two optical paths between predetermined light and an incident position of the predetermined light. The plurality of optical elements are generated by the interferometer, an incident step of entering an interferometer including 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, and the interferometer. A second light receiving step for photoelectrically converting the interference light of the measured light, a sampling step for obtaining a plurality of measurement data by sampling the output of the second light receiving step at a predetermined sampling timing, and the sampling step. A spectrum calculating step for obtaining a spectrum of the light under measurement using Fourier transform based on an interferogram of the light under measurement based on a plurality of measurement data; And a timing generation step of generating a pulling timing, the timing generation step, characterized by timing generating method der Rukoto for Fourier transform spectrometer described above.

Since the Fourier transform spectroscopic method having such a configuration includes an adjustment step of adjusting the sampling timing so that the optical path differences between two measurement data adjacent to each other are equal to each other in the plurality of measurement data, Generation of false spectrum can be reduced. The Fourier transform type spectroscopic method having such a configuration can reduce the generation of a false spectrum with a relatively simple configuration of adjusting the reference voltage in the zero cross detection step . The Fourier transform type spectroscopic method having such a configuration can reduce the generation of a false spectrum with a relatively simple configuration of monitoring a spectrum obtained by measurement .

  The Fourier transform spectrometer timing generation device and the Fourier transform spectrometer timing generation method according to the present invention can reduce the generation of false spectra. The present invention can provide such a Fourier transform spectrometer timing generator and a Fourier transform spectrometer and Fourier transform spectrometer using the generation method. The Fourier transform type spectroscopic method can reduce generation of a pseudo spectrum.

It is a block diagram which shows the structure of the Fourier-transform type spectrometer in embodiment. It is a figure which mainly shows the structure of the interferometer in the Fourier-transform-type spectrometer of embodiment. It is a block diagram which shows the structure of the 1st aspect of the zero cross detection part in the Fourier-transform-type spectrometer of embodiment. It is a figure for demonstrating the production | generation operation | movement of the zero cross signal in the Fourier-transform type spectrometer of embodiment. It is a block diagram which shows the structure of the 2nd aspect of the zero cross detection part in the Fourier-transform-type spectrometer of embodiment. It is a block diagram which shows the structure of the 3rd aspect of the zero crossing detection part in the Fourier-transform-type spectrometer of embodiment. It is a figure for demonstrating the production | generation operation | movement of the zero cross signal in the zero cross detection part of the structure of a 3rd aspect while showing the mode of the false spectrum generate | occur | produced by monochromatic light. Shows the appearance of the false spectrum generated by the light transmitted through the bandpass filter of the predetermined wavelength band that cuts the light of the wavelength band of the false spectrum, and explains the generation operation of the zero cross signal in the zero cross detection unit of the configuration of the third aspect It is a figure for doing.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. 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 illustrating a configuration of a Fourier transform spectrometer according to the embodiment. FIG. 2 is a diagram mainly illustrating a configuration of an interferometer in the Fourier transform spectrometer according to the embodiment. FIG. 3 is a block diagram illustrating a configuration of a first aspect of a zero cross detection unit in the Fourier transform spectrometer of the embodiment.

  A Fourier transform spectrometer (hereinafter abbreviated as “FT spectrometer”) D in the embodiment is an apparatus for measuring a spectrum of light to be measured, and measures the light to be measured with an interferometer. This is a device for obtaining the spectrum of the light to be measured by Fourier transforming the waveform (interferogram) of the measured interference light of the light to be measured. More specifically, the FT spectrometer D of the present embodiment samples an electrical signal obtained by photoelectrically converting the interference light of the light to be measured generated by the interferometer at a predetermined sampling timing. Is a device that obtains a spectrum of measured light using Fourier transform based on an interferogram of the measured light based on the obtained plurality of measured data. Then, in the FT spectrometer D of the present embodiment, in order to improve the S / N ratio and obtain a good accuracy result, the transformation target to be Fourier-transformed to obtain the spectrum of the light to be measured includes the interference. An interferogram obtained by integrating a plurality of interferograms of the light to be measured generated by a meter (hereinafter referred to as “integrated interferogram”) is used.

  Such an FT spectrometer D, for example, as shown in FIGS. 1 to 3, is reflected by the measurement light source unit 50 for irradiating the measurement light to the sample SM, which is an object to be measured, and the sample SM. The reflected light of the measurement light is incident as the measurement light, and the interferometer 11 that emits the interference light of the measurement light, and the interference light of the measurement light obtained by the interferometer 11 are received and photoelectrically converted. A light receiving processing unit 20 that outputs an electric signal related to the waveform of the interference light of the light to be measured (an electric signal representing a light intensity change in the interference light of the light to be measured); A timing generation unit 30 that generates a sampling timing, a control calculation unit 41, an input unit 42, and an output unit 43 are provided.

  The measurement light source unit 50 is a device that irradiates the sample SM with measurement light with a predetermined geometry, and includes, for example, a measurement light source 51 (see FIG. 2) and its peripheral circuits. The measurement light source 51 is a device that 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 used to measure the spectrum of the reflected light in the sample SM, and is light having a continuous spectrum in a predetermined wavelength band set in advance. In this embodiment, for example, a halogen lamp is used as such a measurement light source 51.

  In the FT spectrometer D 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. Reflected by the SM, the reflected light of the reflected measurement light 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 enters the interferometer 11 as the light to be measured.

  In this example, the light to be measured is reflected light of the measurement light reflected by the sample SM. However, the light to be measured may be transmitted light that has passed through the sample SM, or may be irradiated from the sample SM by irradiating the measurement light. The light may be light that is re-radiated (for example, fluorescence emission), or may be light that is emitted by the sample SM without being irradiated with the measurement light. The FT spectrometer D can measure not only the reflected light but also such transmitted light, re-radiated light, and self-luminous light.

  The interferometer 11 receives the light to be measured, branches the incident light to be measured into two first and second light to be measured, and each of the branched first and second light to be measured, It travels (propagates) to each of the first and second optical paths, which are two different paths, and merges again. Between this branch point (branch position) and a merge point (merging position, interference position) If there is an optical path difference between the first and second optical paths, a phase difference is generated at the time of merging, so that interference fringes are generated by the merging. As the interferometer 11, for example, an interferometer having various types of first and second optical paths such as a Mach-Zehnder interferometer can be used. In this embodiment, as shown in FIG. It is constituted by.

  More specifically, as shown in FIG. 2, the interferometer 11 includes a semi-transparent mirror (half mirror) 112, a fixed mirror 114, and a moving mirror 115 whose light reflecting surface moves in the optical axis direction as a plurality of optical elements. The fixed mirror 114 and the movable mirror 115 are arranged so that the normals of the mirror surfaces are orthogonal to each other, and the semi-transparent mirror 112 has a normal line corresponding to each of the normal lines of the fixed mirror 114 and the movable mirror 115. Are arranged so as to cross each normal line at an angle of 45 degrees. In the interferometer 11, the light to be measured incident on the interferometer 11 is branched into two first and second light to be measured by the semi-transparent mirror 112. The branched first first measured light is reflected by the semi-transparent mirror 112 and enters the fixed mirror 114. The first light to be measured 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 second measured light passes through the semi-transparent mirror 112 and enters the movable mirror 115. This second light to be measured 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 light to be measured reflected by the fixed mirror 114 and the second light to be measured reflected by the moving mirror 115 are merged with each other by the semi-transparent mirror 112 and interfere with each other. In the Michelson interferometer 11 having such a configuration, the light to be measured is incident on the interferometer 11 along the normal direction on the mirror surface of the movable mirror 115, and the interference light of the light to be measured is reflected on the mirror surface of the fixed mirror 114. The light is emitted from the interferometer 11 along the normal direction.

  In this embodiment, the interferometer 11 is arranged on the reflection side of the semi-transparent mirror 112 reflected by the semi-transparent mirror 112 when the light to be measured is branched into two first and second measured light beams by the semi-transparent mirror 112. A phase compensation plate 113 is further provided. That is, in the present embodiment, the first measured light reflected by the semi-transparent mirror 112 is incident on the fixed mirror 114 via the phase compensation plate 113, and the first measured light reflected by the fixed mirror 114 is phase compensated. The light enters the semi-transparent mirror 112 again through the plate 113. The phase compensation plate 113 is a phase difference between the first measured light and the second measured light, which is caused by the difference in the number of times the first measured light is transmitted through the semi-transparent mirror 112 and the number of times the second measured light is transmitted through the semi-transmissive mirror 112. Is used to compensate for the phase difference.

  Therefore, in the present embodiment, the first measured light is transmitted from the incident position of the measured light through the semi-transparent mirror 112, the phase compensation plate 113, the fixed mirror 114, and the phase compensation plate 113 in this order. Follow the first optical path that leads to again. The second measured light follows a second optical path from the incident position of the measured light to reach the semi-transmissive mirror 112 again through the semi-transmissive mirror 112 and the movable mirror 115 in this order. By providing this phase compensation plate 113, the interferometer 11 of the FT spectrometer D generates interference fringes due to the optical path difference generated by the moving mirror 115.

  In this embodiment, the movable mirror 115 is an example of an optical path difference forming optical element, and is an optical element that generates an optical path difference between two first and second optical paths by using, for example, resonance vibration. . The movable mirror 115 reciprocates twice or more in the optical axis direction in order to generate a plurality of interferograms of the light to be measured. Examples of such a movable mirror 115 include a light reflecting mechanism disclosed in Japanese Patent Application Laid-Open Nos. 2011-80854 and 2012-42257. The light reflecting mechanism is disposed between the first and second leaf spring portions disposed opposite to each other and the first and second leaf spring portions spaced apart from each other. The first and second supports connected to the second leaf spring portion, and the second support relative to the first support in the opposing direction of the first and second leaf spring portions. And a drive unit that translates the body. In this light reflecting mechanism, in the movement direction of the second support, the thickness of the first and second supports is thicker than that of the first and second leaf springs. A reflection film is formed on one end surface of the support body 2 perpendicular to the moving direction, and the second support body is formed with the first and second leaf spring portions so that the reflection film is exposed. It is connected. Such a light reflection mechanism reciprocates the reflection film by resonance vibration, and is manufactured by, for example, a MEMS (Micro Electro Mechanical Systems) technique.

  In the present embodiment, for example, a collimator lens 111 is disposed as an incident optical system at an appropriate position between the sample surface SF and the semi-transparent mirror 112 in order to cause the light to be measured to enter the semi-transparent mirror 112 with parallel light. In order to collect the interference light of the light to be measured generated by combining the first and second light to be measured with the semi-transparent mirror 112 and causing them to interfere with each other, For example, a condensing lens 116 is further disposed as an emission optical system at an appropriate position between the light receiving unit 21 and the light receiving unit 21.

  Returning to FIG. 1, the light reception processing unit 20 is an electrical signal obtained by receiving and photoelectrically converting the interference light of the light to be measured generated by the interferometer 11, in the interference light of the light to be measured. A circuit that sequentially outputs a plurality of measurement data by sampling an electrical signal corresponding to the light intensity at a predetermined sampling timing. For example, the first light receiving unit 21, the amplification unit 22, and the analog-digital conversion unit (Hereinafter referred to as “AD converter”) 23.

  The first light receiving unit 21 receives the interference light of the light to be measured generated by the interferometer 11 and photoelectrically converts it, thereby an electric signal (first light reception signal) corresponding to the light intensity in the interference light of the light to be measured. Is a circuit that outputs. The first light receiving unit 21 is for light to be measured. The FT spectrometer D of the present embodiment is, for example, a specification whose measurement object is 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 to 2500 nm or less. The first light receiving unit 21 is, for example, an infrared sensor configured by including an InGaAs photodiode and its peripheral circuit. The amplifying unit 22 is an amplifier that amplifies the output of the first light receiving unit 21 with a predetermined amplification factor set in advance. The AD conversion unit 23 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 executed at the zero cross timing of the zero cross signal input from the zero cross detection unit 37a described later.

  The timing generation unit 30 is a device for generating the sampling timing of the AD conversion unit 23, and includes, for example, a timing generation light source 31, a second light receiving unit 36, and a zero cross detection unit 37a. Then, the timing generation unit 30 obtains the interference light of the laser light emitted from the timing generation light source 31 with the interferometer 11, as shown in FIG. 2, a collimator lens 32, an optical multiplexer 33, An optical demultiplexer 34 and a condenser lens 35 are further provided.

  The timing generation light source 31 is a light source device that emits monochromatic laser light having a known wavelength. In FIG. 2, a collimator lens 32 and an optical multiplexer 33 are incident optical systems for causing the laser light emitted from the timing generation 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 measured light, and a collimator so that the normal line intersects the normal line (optical axis) of the movable mirror 115 at 45 degrees. It is disposed between the lens 111 and the semi-transparent mirror 112. The collimator lens 32 is, for example, a biconvex lens, and the laser light emitted from the timing generation light source 31 is incident on the optical multiplexer 33 arranged in this manner at an incident angle of 45 degrees as appropriate. It is arranged in the position. The optical demultiplexer 34 and the condensing lens 35 are emission optical systems for taking out the interference light of the laser light generated by the interferometer 11 from the interferometer 11. The optical demultiplexer 34 is, for example, a dichroic mirror that reflects the interference light of the laser light and transmits the interference light of the light to be measured, and its normal line is 45 degrees with respect to the normal line (optical axis) of the fixed mirror 114. Are arranged between the semi-transparent mirror 112 and the condenser lens 116 so as to intersect each other. The condensing lens 35 is, for example, a biconvex lens, and condenses the interference light of the laser beam emitted at an emission angle of 45 degrees in the optical demultiplexer 34 arranged in this manner, thereby the second light receiving unit 36. To enter.

  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 timing generation light source 31 is converted into the collimator lens 32. The optical path is bent by about 90 degrees by the dichroic mirror 33 of the optical multiplexer 33 and travels along the optical axis of the interferometer 11 (normal direction on the mirror surface of the movable mirror 115). . Therefore, this laser light travels in the interferometer 11 as with the light to be measured, and the interferometer 11 generates the interference light. Then, the interference light of this laser light is bent by about 90 degrees by the dichroic mirror 34 of the optical demultiplexer 34, taken out from the interferometer 11, collected by the condenser lens 35, and condensed by the second light receiving unit 36. Is received.

  Returning to FIG. 1, the second light receiving unit 36 receives and photoelectrically converts the interference light of the laser light obtained by the interferometer 11, thereby performing an electrical signal (first signal) corresponding to the light intensity of the interference light of the laser light. 2 light receiving signal). The second light receiving unit 36 is for monochromatic light (for timing generation). 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 beam to the zero cross detection unit 37a.

  The zero cross detection unit 37a 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 signal is output to the AD conversion unit 23. 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 becomes the zero level. When the movable mirror 115 of the interferometer 11 is moved in the optical axis direction, the movable mirror 115 is moved from the semi-transparent mirror 112 to the phase of the laser light that has returned from the semi-transparent mirror 112 to the semi-transparent mirror via the fixed mirror 114. Since the phase of the laser light that has returned to the semi-transparent mirror is shifted again, the interference light of the laser light becomes strong and weak in a sine wave shape according to the amount of movement. 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 There is a 2π shift before and after. For this reason, the interference light of the laser light repeats the intensity in a sine wave shape as the movable mirror 115 moves. The zero cross detector 37a detects the zero cross of the electric signal that repeats the strength in a sine wave form. The zero-cross detection unit 37a outputs a zero-cross signal to the AD conversion unit 23 at the detected zero-cross timing. When the AD conversion unit 23 receives the zero-cross signal, the zero-cross signal is input from the first light receiving unit 21 at the zero-cross timing. The electrical signal corresponding to the light intensity of the interference light of the measured light is sampled and AD converted.

  In the present embodiment, for example, as shown in FIG. 3, such a zero-cross detection unit 37 a includes a comparator 371, a reference voltage generation circuit 372, an adjustment sine wave generation circuit 373, and an edge detection circuit 374. Prepare.

  The reference voltage generation circuit 372 is a circuit that generates a reference voltage, and outputs the generated reference voltage to the comparator 371. The voltage value of the reference voltage generated by the reference voltage generation circuit 372 is controlled by a reference voltage adjustment unit 415a of the control calculation unit 41 described later.

  The adjustment sine wave generation circuit 373 is a circuit that generates an adjustment sine wave signal used to adjust the voltage value of the reference voltage generated by the reference voltage generation circuit 372. This sine wave signal for adjustment is a signal in which the time lengths of the half cycles at the center of the amplitude are equal to each other. This sine wave signal for adjustment may be an output of the second light receiving unit 36 obtained by photoelectrically converting the interference light of the monochromatic laser beam in the timing generation light source 31 or may be prepared separately. . Therefore, the adjustment sine wave generation circuit 373 may include, for example, the timing generation light source 31, the interferometer 11, and the second light receiving unit 36. For example, the adjustment sine wave generation circuit 373 includes the duty ratio. A square wave generation circuit that generates a square wave (rectangular wave) signal having a frequency of 50%, and a low-pass filter that filters (filters) the square wave signal generated by the square wave generation circuit. Alternatively, the adjustment sine wave generation circuit 373 may include a DA converter, for example.

  In the case of measuring the light to be measured, the comparator 371 compares the output of the second light receiving unit 36 with the reference voltage of the reference voltage generating circuit 372, and the output of the second light receiving unit 36 is the reference voltage of the reference voltage generating circuit 372. This circuit outputs a comparison result signal to the edge detection circuit 374 when the voltage is equal to or higher than the voltage. The comparator 371 compares the output of the adjustment sine wave generation circuit 373 with the reference voltage of the reference voltage generation circuit 372 when adjusting the voltage value of the reference voltage generated by the reference voltage generation circuit 372. When the output of the adjusted sine wave generation circuit 373 is equal to or higher than the reference voltage of the reference voltage generation circuit 372, the comparison result signal is output to the reference voltage adjustment unit 415a. This comparison result signal is a square wave because it is output when the sine wave signal of the adjustment sine wave generation circuit 373 is equal to or higher than the reference voltage of the reference voltage generation circuit 372.

  When adjusting the voltage value of the reference voltage, as described above, if the output itself of the second light receiving unit 36 is used, the adjustment is suitable for a monochromatic laser beam used when actually measuring the measured light. Has the advantage that can be performed. Further, since the output of the second light receiving unit 36 that is always obtained when actually measuring the light to be measured is used, it is possible to always adjust the voltage value of the reference voltage. On the other hand, the wavelength of the monochromatic laser beam in the timing generation light source 31 is relatively short in order to obtain measurement data with high resolution, and the output of the second light receiving unit 36 has a relatively high frequency. For this reason, the sine wave signal by this monochromatic laser beam has a short cycle, and it is difficult to increase the resolution in adjusting the voltage value of the reference voltage. Therefore, it is possible to increase the resolution by measuring and integrating the high period and the low period in the square wave signal a plurality of times.

  On the other hand, as described above, when the adjustment sine wave generation circuit 373 for generating the adjustment sine wave signal is separately provided, it is possible to use a sine wave signal having a relatively long period. A mode in which the generation circuit 373 is separately provided can easily increase the resolution in the adjustment of the voltage value of the reference voltage. In the aspect in which the adjustment sine wave generation circuit 373 is separately provided, for example, the reference voltage of the reference voltage generation circuit 372 is used by using the separate adjustment sine wave generation circuit 373 during the manufacturing of the FT spectrometer D. After the adjustment, the FT spectrometer D may be manufactured by connecting the second light receiving unit 36 to the comparator 371.

  The edge detection circuit 374 detects a rising edge in the square wave comparison result signal output from the comparator 371. When this rising edge is detected, the edge detection circuit 374 outputs a pulse signal to the AD conversion unit 23 as a sampling timing, and the comparator This is a circuit that detects a falling edge in the square wave comparison result signal output from the oscillator 371 and outputs a pulse signal to the AD conversion unit 23 as a sampling timing when the falling edge is detected.

  Returning to FIG. 1, the control calculation unit 41 controls each part of the FT spectrometer D according to the function of each part in order to obtain the spectrum of the measured light, and the interferogram of the measured light. Based on the above, the spectrum of the light to be measured is obtained using Fourier transform. 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 Only) that stores various programs executed by the CPU and data necessary for the execution in advance. The microcomputer includes a nonvolatile memory element such as a memory, a volatile memory element such as a RAM (Random Access Memory) serving as a so-called working memory of the CPU, and peripheral circuits thereof. The control calculation unit 41 may further include a relatively large capacity storage device such as a hard disk, for example, in order to store data output from the AD conversion unit 23. The control calculation unit 41 is functionally executed by executing a program, and the sampling data storage unit 411, the center burst position calculation unit 412, the integrated interferogram calculation unit 413, the spectrum calculation unit 414, and the reference voltage adjustment unit 415a is configured.

  The sampling data storage unit 411 stores measurement data related to the interference light of the light to be measured output from the AD conversion unit 23. As described above, the measurement data is obtained by sampling the electrical signal corresponding to the light intensity in the interference light of the light to be measured by the AD conversion unit 23 at the timing of the zero cross detected by the zero cross detection unit 37a.

  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 integrated interferogram calculation unit 413 aligns a plurality of interferograms obtained by continuously measuring the measured light at a plurality of times at each center burst position obtained by the center burst position calculation unit 412. While performing, the integrated interferogram is obtained by integrating.

  The spectrum calculation unit 414 obtains a spectrum by performing Fourier transform on the integrated interferogram obtained by integrating a plurality of interferograms by the integrated interferogram calculating unit 413.

  The reference voltage adjusting unit 415a adjusts the zero-cross timing used as the sampling timing, so that the reference voltage described above is set so that the optical path differences between two adjacent measurement data are equal to each other in a plurality of measurement data. The voltage value of the reference voltage generated by the generation circuit 372 is adjusted.

  The input unit 42, 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, for example. A device that inputs various data necessary for measurement to the FT spectrometer D, such as a keyboard and a mouse. The output unit 43 is a device that outputs the command and data input from the input unit 42 and the spectrum of the light to be measured measured by the FT spectrometer D. For example, the output unit 43 is a CRT display, LCD, organic EL display, and plasma. A display device such as a display, or a printing device such as a printer.

  Next, the operation of this embodiment will be described. In the FT spectrometer D having such a configuration, when measuring the sample SM to be measured, first, the sample SM is set in the FT spectrometer D, and measurement is started. When the measurement is started, the measurement light source 51 emits measurement light and irradiates the sample SM with the measurement light at an incident angle of 45 degrees, for example. Then, the reflected light of the measurement light reflected by the sample SM is measured from the 0 degree direction as light to be measured, and is incident on the interferometer 11.

  The light to be measured 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 light to be measured by the interferometer 11. More specifically, the light to be measured is converted into parallel light by the collimator lens 111, and is reflected and transmitted by the semi-transparent mirror 112 through the optical multiplexer 33, thereby being branched into the first and second light to be measured. The first light to be measured branched by being 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 traces the optical path that has come in reverse, and again the semi-transparent mirror 112. Return to. On the other hand, the second light to be measured 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 light to be measured reflected by the fixed mirror 114 and the second light to be measured reflected by the moving mirror 115 are merged with each other by the semi-transparent mirror 112 and interfere with each other. The interference light of the light to be measured 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 measurement light, and outputs an electrical signal corresponding to the light intensity in the interference light of the measurement light to the amplification unit 22. The amplifying unit 22 amplifies the electric signal corresponding to the interference light of the light to be measured with a predetermined amplification factor, and outputs it to the AD converting unit 23.

  On the other hand, the FT spectrometer D also captures monochromatic laser light emitted from the timing generation light source 31. This laser light is incident on the interferometer 11 via the optical multiplexer 33, interferes with the interferometer 11 in the same manner as described above, becomes interference light of the laser light, and passes through the optical demultiplexer 34 to the second light receiving unit. Light is received at 36. The second light receiving unit 36 photoelectrically converts the incident interference light of the laser beam, and outputs an electrical signal corresponding to the light intensity in the interference light of the laser beam to the zero cross detection unit 37a. The zero cross detection unit 37a detects a timing at which the electric signal corresponding to the interference light of the laser beam becomes zero as a zero cross timing, and outputs the zero cross timing to the AD conversion unit 23 as a sampling timing (AD conversion timing).

  While such measured light and laser light are respectively taken into the interferometer 11, the movable mirror 115 of the interferometer 11 is moved along the optical axis direction according to the control of the control calculation unit 41 by resonance vibration. Yes.

  The AD conversion unit 23 samples the electrical signal output from the amplification unit 22 according to the light intensity in the interference light of the light to be measured at the zero cross timing input from the zero cross detection unit 37a, and converts the electrical signal from an analog signal to a digital signal. AD conversion is performed, and the electric signal of the digital signal subjected to the AD conversion is output to the control calculation unit 41.

  By operating in this way, measurement data in the interferogram of the light to be measured is output from the AD conversion unit 23 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 light to be measured is measured in a similar manner continuously several times in accordance with the reciprocation of the movable mirror 115, and these Each measurement data of each interferogram is stored in the sampling data storage unit 411. That is, when the movable mirror 115 reciprocates once, one scan is completed, and interferogram measurement data is obtained.

  Next, the center burst position calculation unit 412 obtains the position of the center burst in the interferogram of the measured light for each measurement data of each interferogram stored in the sampling data storage unit 411.

  Next, the integrated interferogram calculation unit 413 aligns the plurality of interferograms of the light to be measured, obtained by measuring a plurality of times, at each center burst position obtained by the center burst position calculation unit 412. The integrated interferogram for the light to be measured is obtained by performing integration.

  Next, the spectrum calculation unit 414 obtains the spectrum of the light to be measured by subjecting the accumulated interferogram obtained by the accumulated interferogram calculation unit 413 to Fourier transform.

The calculation of this spectrum will be described more specifically. First, the interferogram F _m (x _i ) in the m-th measurement has an optical path difference x _i , a wave number ν _j , and a wave number ν _j spectrum. When the amplitude is B (ν _j ), the position of the optical path difference 0 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.

  When the accumulated interferogram is obtained by the accumulated interferogram calculating unit 413 in this way, the spectrum calculating unit 414 obtains the spectrum of the light to be measured by, for example, fast Fourier transform (FFT) of the accumulated 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, and the amplitude | B _window (ν _j ) | of the spectrum of the light to be measured is obtained (Expression 4).

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

  Next, adjustment of sampling timing will be described. FIG. 4 is a diagram for explaining the operation of generating a zero-cross signal in the Fourier transform spectrometer according to the embodiment. FIG. 4A is a time chart showing a case where zero-cross signals output from the zero-cross detector 37a are output at unequal time intervals, and FIG. 4B is a zero-cross of FIG. 4A. It is a time chart which shows the case where a signal becomes equal intervals at time intervals. 4A and 4B, the upper part is a sine wave signal indicating the output of the second light receiving unit 36, the middle part is a square wave signal indicating the output of the comparator 371, and the lower part is edge detection. This is a pulse signal of a zero cross signal indicating the output of the circuit 374, that is, the output of the zero cross detector 37a.

  Here, in the measurement of the spectrum of the light to be measured, when the zero cross signal representing the zero cross timing used as the sampling timing in the AD conversion unit 23 is not output at a desired timing from the zero cross detection unit 37a, The measurement data converted by the AD conversion unit 23 at such sampling timing is periodically repeated when the optical path difference between adjacent measurement data is long, short, long, short, and so on. A pseudo spectrum is generated in the spectrum of the light to be measured obtained by Fourier transforming the interferogram.

  For example, the reference voltage output from the reference voltage generation circuit 372 as shown in FIG. 4A due to the offset voltage of the comparator 371, the frequency characteristics of the gain in the electric / electronic circuit, the mirror tilt error of the optical system, or the like. However, if it deviates from the center of the amplitude in the sine wave signal output from the second light receiving unit 36, the duty ratio of the square wave signal output from the comparator 371 deviates from 50%. As a result, the edge detection circuit 374 outputs the zero cross signal at each timing by detecting the rising timing and the falling timing in the square wave signal, so that the square wave signal with the duty ratio deviating from 50% is output. Is input, the edge detection circuit 374 outputs a zero-cross signal at time intervals of periodic repetition of long, short, long, short,... In the above example, the edge detection circuit 374 repeatedly outputs the zero cross signal at a time ratio of 4: 6.

  For this reason, in the FT spectrometer D of the present embodiment, the reference voltage of the reference voltage generation circuit 372 is adjusted so that the optical path differences between two adjacent measurement data are equal to each other. In other words, this means that the reference voltage of the reference voltage generation circuit 372 is adjusted so that the zero cross signals (sampling timing) output from the edge detection circuit 374 (zero cross detection unit 37) are equally spaced in time. This means that the reference voltage of the reference voltage generation circuit 372 is adjusted so that the duty ratio of the square wave signal output from the comparator 371 is 50%. Means that the reference voltage of the reference voltage generation circuit 372 is adjusted so as to coincide with the center of the amplitude of the sine wave signal.

  More specifically, first, an adjustment sine wave signal (the output itself of the second light receiving unit 36 or a separately prepared signal) is input to the comparator 371 from the adjustment sine wave generation circuit 373. The comparator 371 compares the output of the adjustment sine wave generation circuit 373 with the reference voltage of the reference voltage generation circuit 372, and the output of the adjustment sine wave generation circuit 373 is equal to or higher than the reference voltage of the reference voltage generation circuit 372. A square wave signal is output to the reference voltage adjustment unit 415a as the comparison result signal.

  When the square wave signal is input, the reference voltage adjusting unit 415a continues the first time interval from the rising timing to the falling timing in the square wave signal, and then the first time interval from the falling timing to the next rising timing. Measure at 2 hour intervals. This measurement is performed as follows, for example. When the reference voltage adjusting unit 415a detects the rising edge in the square wave signal, the time is started after the resetting by a time counting means such as a counter that counts up at a constant time interval, and when the falling edge in the square wave signal is detected, The time measurement by the time measuring means is terminated and the first time interval is obtained. Similarly, when the reference voltage adjusting unit 415a detects the falling edge in the square wave signal, the time measuring means starts time measurement after resetting the time, and when detecting the rising edge in the square wave signal, the time measuring means ends the time counting. A second time interval is determined. In addition, in order to measure the first time interval and the second time interval with higher accuracy, the first time interval and the second time interval are respectively measured a plurality of times, and average values thereof are obtained, respectively. May be the first time interval and the second time interval, respectively.

  Next, the reference voltage adjustment unit 415a determines whether or not the obtained first time interval and second time interval coincide with each other within a preset allowable error range.

  As a result of this determination, when the obtained first time interval and second time interval coincide with each other within a preset allowable error range, the reference voltage adjustment unit 415a generates the reference voltage generation circuit 372. The edge detection circuit 374 (zero cross detection unit 37a) outputs a zero cross signal (sampling timing) such that the optical path difference between adjacent measurement data becomes equal intervals with the current voltage value Vt of the reference voltage being Therefore, the current voltage value Vt is maintained, and the reference voltage adjustment process is terminated.

  On the other hand, as a result of this determination, when the obtained first time interval and second time interval do not match within a preset allowable error range, the reference voltage adjustment unit 415a sets the reference voltage generation circuit 372 to The reference voltage is changed from the voltage value Vt of the current reference voltage by a predetermined value ΔV set in advance. In this change, when the first time interval is shorter than the second time interval, that is, when the duty ratio of the square wave signal is smaller than 50%, the voltage of the current reference voltage generated by the reference voltage generation circuit 372 Since the value Vt is on the higher voltage side than the center of the amplitude in the adjustment sine wave signal of the adjustment sine wave generation circuit 373, the reference voltage adjustment unit 415a controls the reference voltage generation circuit 372 to control the current reference voltage. The reference voltage is changed so as to be lowered from the voltage value Vt by a predetermined value ΔV set in advance. On the other hand, when the first time interval is longer than the second time interval, that is, when the duty ratio of the square wave signal is larger than 50%, the voltage value Vt of the current reference voltage generated by the reference voltage generation circuit 372. Is on the lower voltage side than the center of the amplitude in the adjustment sine wave signal of the adjustment sine wave generation circuit 373, the reference voltage adjustment unit 415a controls the reference voltage generation circuit 372 to control the voltage of the current reference voltage. The reference voltage is changed so as to increase from the value Vt by a preset predetermined value ΔV.

  Then, after changing the voltage value of the reference voltage, the reference voltage adjustment unit 415a again measures the first time interval and then the second time interval, respectively, and obtains the calculated first time. It is determined whether or not the time interval and the second time interval match within a preset allowable error range. The reference voltage adjustment unit 415a performs the measurement of the first and second time intervals, the coincidence determination between the first time interval and the second time interval, and the change of the reference voltage as the first time interval and the second time interval. Is performed within the allowable error range.

  When the reference voltage of the reference voltage generation circuit 372 is adjusted in this way, the amplitude of the reference voltage of the reference voltage generation circuit 372 in the sine wave signal output from the second light receiving unit 36 as shown in FIG. Therefore, the comparator 371 outputs a square wave signal with a duty ratio of 50% to the edge detection circuit 374. As a result, the edge detection circuit 374 (zero cross detection unit 37) outputs zero cross signals (sampling timing) at regular intervals. Therefore, the optical path difference between two adjacent measurement data becomes equal to each other, and the FT spectrometer D has a spectrum with reduced errors caused by non-uniform optical path difference between adjacent measurement data. The generation of false spectrum can be reduced.

  In the FT spectrometer D of the above-described embodiment, the generation of the false spectrum is reduced with a relatively simple configuration of adjusting the reference voltage of the zero-cross detection unit 37a.

  Further, in the above-described FT spectrometer D of the present embodiment, the generation of the false spectrum is reduced with a relatively simple configuration in which the duty ratio of the square wave signal output from the comparator 371 is 50%, in other words. This is realized with a relatively simple configuration in which the periods of the zero cross signal (sampling timing) are equally spaced.

  The above-described adjustment of the reference voltage may be performed, for example, at the manufacturing stage or the shipping stage of the FT spectrometer D, or may be performed before the measurement of the FT spectrometer D, for example. The adjustment of the reference voltage before the measurement of the FT spectrometer D may be performed for each measurement, for each of a plurality of measurements, or for each fixed period.

  In addition, the adjustment of the reference voltage described above may be performed separately for the forward path and the return path of the movable mirror 115, and the reference voltage for the forward path of the movable mirror 115 and the reference voltage for the return path of the movable mirror 115, respectively. It may be set.

  Moreover, in the FT type | mold spectrometer D in the above-mentioned embodiment, although the zero cross detection part 37 is the zero cross detection part 37a of the 1st aspect shown in FIG. 3, another aspect is also possible. FIG. 5 is a block diagram illustrating a configuration of a second aspect of the zero-cross detection unit in the Fourier transform spectrometer according to the embodiment. FIG. 6 is a block diagram illustrating a configuration of a third aspect of the zero-cross detection unit in the Fourier transform spectrometer according to the embodiment. FIG. 7 is a diagram for explaining a zero-cross signal generation operation in the zero-cross detection unit having the configuration of the third aspect while showing a state of a false spectrum generated by monochromatic light. FIG. 8 shows a state of a false spectrum generated by light transmitted through a bandpass filter of a predetermined wavelength band for cutting light of a wavelength band of the false spectrum, and the zero-cross signal in the zero-cross detection unit having the configuration of the third aspect. It is a figure for demonstrating production | generation operation | movement.

  The zero-cross detection unit 37b of the second aspect illustrated in FIG. 5 is a device that includes a selection switch that selects a signal input to the comparator 371. More specifically, the zero-cross detection unit 37b of the second aspect includes a comparator 371, a reference voltage generation circuit 372, an adjustment sine wave generation circuit 373, an edge detection circuit 374, and a selection switch 375. In the case of the zero-cross detection unit 37b of the second mode, the calculation control unit 41 replaces the reference voltage adjustment unit 415a provided corresponding to the zero-cross detection unit 37a of the first mode, and the reference voltage adjustment unit 415b. It has.

  In the comparator 371, the reference voltage generation circuit 372, the adjustment sine wave generation circuit 373, and the edge detection circuit 374 in the zero cross detection unit 37b of the second mode, the adjustment sine wave signal is not the output of the second light receiving unit 36. The comparator in the zero-cross detector 37a of the first aspect is a signal provided separately, except that the adjustment sine wave generation circuit 373 is a circuit that generates the adjustment sine wave signal provided separately. Since it is the same as each of the oscillator 371, the reference voltage generation circuit 372, the adjustment sine wave generation circuit 373, and the edge detection circuit 374, description thereof is omitted.

  The selection switch 375 outputs a signal input to the comparator 371 as a comparison target to be compared with the reference voltage of the reference voltage generation circuit 372, out of the output of the second light receiving unit 36 and the output of the adjustment sine wave generation circuit 373. It is a switch circuit that switches to either one according to the control of the reference voltage adjustment unit 415b. The selection switch 375 has two inputs and one output, and one input terminal is connected to the output terminal of the second light receiving unit 36, and the other input terminal is connected to the output terminal of the adjustment sine wave generation circuit 373. The output terminal is connected to the comparator 371. The selection switch 375 includes a switch element such as a transistor, for example.

  Similarly to the reference voltage adjustment unit 415a, the reference voltage adjustment unit 415b adjusts the zero cross timing used as the sampling timing so that the optical path difference between two adjacent measurement data in each of the plurality of measurement data is mutually different. The voltage value of the reference voltage generated by the above-described reference voltage generation circuit 372 is adjusted so as to be equal. The reference voltage adjustment unit 415b further has a function of performing switching control for switching the connection state between the input terminal and the output terminal in the selection switch 375. When measuring the light to be measured, the reference voltage adjustment unit 415b uses the one input terminal to which the output terminal of the second light receiving unit 36 in the selection switch 375 is connected, and the output of the second light receiving unit 36 is a comparator. The selection switch 375 performs switching control connected to the output terminal so that the reference voltage is adjusted, and the reference voltage adjustment unit 415b adjusts the sine for adjustment in the selection switch 375. The selector switch 375 switches the switching control for connecting the other input terminal to which the output terminal of the wave generation circuit 373 is connected to the output terminal so that the output of the adjustment sine wave generation circuit 373 is output to the comparator 371. To do.

  In the FT spectrometer D including the zero-cross detection unit 37b of the second aspect as described above, when measuring the light to be measured, the output of the second light receiving unit 36 is input to the comparator 371 by the reference voltage adjustment unit 415b. As described above, when the selection switch 375 is controlled and the reference voltage is adjusted, the output of the adjustment sine wave generation circuit 373 is input to the comparator 371 by the reference voltage adjustment unit 415b. The selection switch 375 is controlled. Then, the reference voltage in the zero-cross detection unit 37b of the second mode is adjusted by the same operation as the zero-cross detection unit 37a of the first mode. Therefore, the zero-cross detection unit 37b of the second aspect has the same operational effects as the zero-cross detection part 37a of the first aspect.

  Further, in the zero-cross detection unit 37c of the third aspect shown in FIG. 6, it is used that the timing generation light source 31 emits monochromatic light with a known wavelength, and the monochromatic light with a known wavelength and the monochromatic light with a known wavelength are used. From the sampling timing adjustment spectrum obtained when the measurement light is used as the measurement light, the monochromatic light generated due to the non-uniformity of the optical path differences between the two measurement data adjacent to each other in the plurality of measurement data The reference voltage of the reference voltage generation unit 372 is adjusted so that the pseudo spectrum component based on it disappears, and thereby, in a plurality of measurement data, the optical path difference between two adjacent measurement data is equal to each other. Sampling timing (zero cross signal) is adjusted.

  Such a zero-cross detection unit 37c of the third aspect includes a comparator 371, a reference voltage generation circuit 372, and an edge detection circuit 374, for example, as shown in FIG. That is, in this third mode, since the monochromatic laser beam of the timing generation light source 31 is used, the output of the second light receiving unit 36 is input to the comparator 371. Therefore, an adjustment sine wave generation circuit provided separately. 373 is unnecessary. In the case of the zero-cross detection unit 37c of the third aspect, the calculation control unit 41 replaces the reference voltage adjustment part 415a provided corresponding to the zero-cross detection part 37a of the first aspect, and the reference voltage adjustment part 415c. It has.

  The comparator 371, the reference voltage generation circuit 372, and the edge detection circuit 374 in the zero cross detection unit 37c of the third aspect are the same as the comparator 371, the reference voltage generation circuit 372, and the edge detection circuit 374 in the zero cross detection part 37a of the first aspect. Since these are the same, the description thereof is omitted.

  Similarly to the reference voltage adjustment unit 415a, the reference voltage adjustment unit 415c adjusts the zero cross timing used as the sampling timing so that the optical path difference between the two measurement data adjacent to each other in the plurality of measurement data is mutually different. The voltage value of the reference voltage generated by the above-described reference voltage generation circuit 372 is adjusted so as to be equal. Here, in the zero-cross detection unit 37c of the third aspect, the reference voltage adjustment unit 415c includes light having a known wavelength and a monochromatic laser beam (an example of monochromatic light) of a timing generation light source (an example of a monochromatic light source). By adjusting the reference voltage of the reference voltage generation circuit 372 so that the false spectrum disappears from the sampling timing adjustment spectrum obtained when the light to be measured is used as the measured light, in the plurality of measurement data, 2 adjacent to each other. The zero cross signal (sampling timing) is adjusted so that the optical path differences between the pieces of measurement data are equal to each other. Therefore, when the reference voltage is adjusted, the spectrum obtained by the spectrum calculation unit 414 is input to the reference voltage adjustment unit 415c as the sampling timing adjustment spectrum.

  This pseudo spectrum is obtained when the wavelength of the spectral component is λpseudo, the wavelength of the light having the known wavelength is λ1, and the wavelength of the monochromatic laser light emitted from the timing generation light source 31 is λ2. 1 / λpseudo = 1 / λ2-1 / λ1 ”is established, and is thus obtained. Thus, the false spectrum appears at the position of the wave number of the difference between the wave number of the monochromatic laser beam emitted from the timing generation light source 31 and the wave number of the light whose wavelength is known. For example, when λ1 = 1310 nm and λ2 = 633 nm, the wavelength of the pseudo spectrum is λpseudo = 1225 nm.

  Therefore, when adjusting the reference voltage of the reference voltage generation circuit 372, first, light having a known wavelength (for example, light having the wavelength of 1310 nm) is incident on the interferometer 11, and the spectrum calculation unit 414 is operated by the above-described operation. Obtains a spectrum and outputs the obtained spectrum to the reference voltage adjustment unit 415c as a sampling timing adjustment spectrum.

  Further, in place of the monochromatic light having the known wavelength, as shown in FIG. 8, light in a wavelength band where a false spectrum appears with respect to white light is cut, and light having the original wavelength that generates the false spectrum is transmitted. Light transmitted through a bandpass filter having a predetermined wavelength band may be used.

  When the sampling timing adjustment spectrum is input, the reference voltage adjustment unit 415c determines whether or not the sampling timing adjustment spectrum includes a false spectrum.

  As a result of this determination, if the false spectrum is not included in the sampling timing adjustment spectrum, the reference voltage adjustment unit 415c uses the current voltage value Vt of the reference voltage generated by the reference voltage generation circuit 372, Since the edge detection circuit 374 (zero cross detection unit 37a) outputs a zero cross signal (sampling timing) such that optical path differences between adjacent measurement data are equally spaced, the current voltage value Vt is maintained, and the reference The voltage adjustment process ends.

  On the other hand, as a result of this determination, for example, as shown in FIGS. 7A and 8A, when the spectrum for sampling timing adjustment includes a false spectrum, the reference voltage adjustment unit 415c The voltage generation circuit 372 is controlled, and the reference voltage is changed from the voltage value Vt of the current reference voltage by a preset predetermined value ΔV. In this change, the reference voltage adjustment unit 415a compares the magnitude of the pseudo spectrum before and after the change, and presets it from the voltage value Vt of the current reference voltage so as to reduce the magnitude of the false spectrum. The reference voltage is changed so as to decrease by the predetermined value ΔV (or increase from the voltage value Vt of the current reference voltage by a preset predetermined value ΔV). The magnitude of the pseudo spectrum is proportional to the amount of deviation from 50% in the duty ratio of the square wave signal (the amount of deviation between the voltage value Vt of the current reference voltage and the center of the amplitude at the output of the second light receiving unit 36). The predetermined value ΔV may be set according to the size of the false spectrum.

  Then, after changing the voltage value of such a reference voltage, the reference voltage adjustment unit 415c again acquires the changed sampling timing adjustment spectrum from the spectrum calculation unit 414, and performs a new sampling timing adjustment after the change. It is determined whether a false spectrum is included in the spectrum for use. The reference voltage adjustment unit 415c performs such acquisition of the sampling timing adjustment spectrum, determination of the presence / absence of the false spectrum, and change of the reference voltage until the false spectrum is not included in the sampling timing adjustment spectrum.

  When the reference voltage of the reference voltage generation circuit 372 is adjusted in this way, the reference voltage of the reference voltage generation circuit 372 is output from the second light receiving unit 36 as shown in FIGS. 7B and 8B. Therefore, the comparator 371 outputs a square wave signal with a duty ratio of 50% to the edge detection circuit 374. As a result, the edge detection circuit 374 (zero cross detection unit 37) outputs zero cross signals (sampling timing) at regular intervals. Therefore, the optical path difference between two adjacent measurement data becomes equal to each other, and the FT spectrometer D has a spectrum with reduced errors caused by non-uniform optical path difference between adjacent measurement data. The generation of false spectrum can be reduced.

  And in FT type | mold spectrometer D provided with the zero crossing detection part 37c of such a 3rd aspect, reduction of generation | occurrence | production of a false spectrum is a comparatively simple structure of monitoring the spectrum obtained with a Fourier-transform type | mold spectrometer, It has been realized.

  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.

D Fourier transform type spectrometer SM Sample 11 Interferometer 31 Timing generation light source 36 Second light receiving units 37a, 37b, 37c Zero cross detection unit 41 Control calculation unit 371 Comparator 372 Reference voltage generation circuit 373 Adjustment sine wave generation circuit 374 Edge Detection circuit 375 Selection switch 411 Sampling data storage unit 412 Center burst position calculation unit 413 Interferogram calculation unit 414 Spectrum calculation units 415a, 415b, 415c Reference voltage adjustment unit

Claims (5)

A plurality of measurement data is obtained by sampling a signal obtained by photoelectrically converting the interference light of the light to be measured generated by the interferometer at a predetermined sampling timing, and the plurality of measurement data obtained are used to obtain the measurement data. In a Fourier transform spectrometer timing generator for generating the sampling timing, used in a Fourier transform spectrometer that obtains the spectrum of the light to be measured using Fourier transform based on an interferogram of the light to be measured.
A light source that emits monochromatic light ;
A light receiving unit that photoelectrically converts the interference light of the monochromatic light generated by the interferometer ;
A reference voltage generator for generating a reference voltage ;
A zero-cross detection unit that outputs a zero-cross signal as the sampling timing at a timing at which the output of the light-receiving unit intersects the reference voltage of the reference voltage generation unit ;
An adjustment unit that adjusts the sampling timing so that the optical path difference between two adjacent measurement data is equal to each other in the plurality of measurement data by adjusting the reference voltage of the reference voltage generation unit; With
The adjustment unit determines that the optical path difference between two adjacent measurement data in the plurality of measurement data is unequal from a sampling timing adjustment spectrum obtained when light having a known wavelength is used as the measurement light. By adjusting the reference voltage of the reference voltage generation unit so that a false spectral component based on the light generated due to the fact disappears, two measurements adjacent to each other in the plurality of measurement data as the optical path difference between the data are equal to each other, a Fourier transform spectrometer timing generator characterized that you adjust the sampling timing. The adjustment unit determines whether or not the false spectrum component is included in the sampling timing adjustment spectrum. If the determination result includes the false spectrum component, the adjustment unit adjusts the current reference voltage. If the false spectral component is not included as a result of the determination, the current reference voltage is maintained so that the false spectral component disappears from the sampling timing adjustment spectrum. by adjusting the reference voltage of the voltage generator, the plurality of measurement data, so that the optical path difference between two adjacent measurement data are equal to each other to each other, and characterized that you adjust the sampling timing The timing generator for Fourier transform spectrometers according to claim 1. A plurality of measurement data is obtained by sampling a signal obtained by photoelectrically converting the interference light of the light to be measured generated by the interferometer at a predetermined sampling timing, and the plurality of measurement data obtained are used to obtain the measurement data. In a Fourier transform spectrometer timing generation method for generating the sampling timing, which is used in a Fourier transform spectrometer that obtains the spectrum of the light to be measured using Fourier transform based on an interferogram of the light to be measured .
A monochromatic light emitting process for emitting monochromatic light ;
A light receiving step for photoelectrically converting the interference light of the monochromatic light generated by the interferometer ;
A reference voltage generating step for generating a reference voltage ;
A zero cross detection step of outputting a zero cross signal as the sampling timing at a timing at which the output of the light receiving step crosses the reference voltage of the reference voltage generation step ;
An adjusting step of adjusting the sampling timing so that optical path differences between two adjacent measurement data are equal to each other in the plurality of measurement data by adjusting the reference voltage in the reference voltage generating step; With
In the adjustment step, an optical path difference between two adjacent measurement data in the plurality of measurement data is unequal from a sampling timing adjustment spectrum obtained when light having a known wavelength is used as the measurement light. By adjusting the reference voltage in the reference voltage generation step so that a false spectral component based on the light generated due to the fact disappears, two measurements adjacent to each other in the plurality of measurement data The timing generation method for a Fourier transform spectrometer, wherein the sampling timing is adjusted so that optical path differences between data are equal to each other. A plurality of optical elements that form two optical paths between the incident position of the predetermined light and the interference position, and the plurality of optical elements move in the optical axis direction by moving in the optical axis direction; An interferometer including an optical path difference forming optical element that generates an optical path difference between two optical paths ;
A second light receiving unit that photoelectrically converts interference light of the light to be measured generated by the interferometer ;
A sampling unit for obtaining a plurality of measurement data by sampling the output of the second light receiving unit at a predetermined sampling timing ;
A spectrum calculation unit for obtaining a spectrum of the light to be measured using Fourier transform based on an interferogram of the light to be measured by a plurality of measurement data obtained by the sampling unit ;
A timing generator for generating the sampling timing ,
The timing generation unit is a timing generation device for a Fourier transform spectrometer according to claim 1 or 2.
A Fourier transform spectrometer . A plurality of optical elements that form two optical paths between predetermined light incident positions and interference positions are provided, and the plurality of optical elements are moved in the optical axis direction to move the two light elements. An incident step of entering an interferometer including an optical path difference forming optical element that generates an optical path difference between the optical paths of
A second light receiving step for photoelectrically converting the interference light of the light to be measured generated by the interferometer ;
A sampling step of obtaining a plurality of measurement data by sampling the output of the second light receiving step at a predetermined sampling timing ;
A spectrum calculating step for obtaining a spectrum of the light to be measured using Fourier transform based on an interferogram of the light to be measured by a plurality of measurement data obtained in the sampling step ;
A timing generation step of generating the sampling timing ,
The timing generation step is a timing generation method for a Fourier transform spectrometer according to claim 3.
A Fourier transform type spectroscopic method characterized by the above .

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