WO2012124294A1

WO2012124294A1 - Fourier transform spectrometer and fourier transform spectrometry

Info

Publication number: WO2012124294A1
Application number: PCT/JP2012/001554
Authority: WO
Inventors: 長井　慶郎; 利夫河野
Original assignee: コニカミノルタセンシング株式会社
Priority date: 2011-03-17
Filing date: 2012-03-07
Publication date: 2012-09-20
Also published as: JPWO2012124294A1; JP5737386B2

Abstract

In this Fourier transform spectrometer and Fourier transform spectrometry, two light paths (a first and second light path) that are formed by means of a plurality of optical elements (112, 114, 115) are provided between the entrance position of light to be measured and an interference position, and a phase difference spectrometer (11) having a phase difference between the light paths is used in a disposition state that disposes the plurality of optical elements in a manner so that the light path difference between the two light paths (first and second light path) becomes zero when supposing that each of the two light paths (first and second light path) are formed from the same medium. The Fourier transform spectrometry and Fourier transform spectrometer having such a configuration use the phase difference spectrometer (11), and so compared to interferograms resulting from interferometers provided with conventional phase compensation plates, the magnitude (level) of the amplitude thereof becomes smaller, and thus it is possible to also detect at a high resolution minute signals in the vicinity of the zero level of the interferogram even with one AD converter.

Description

Fourier transform spectrometer and Fourier transform spectroscopic method

The present invention relates to a spectrometer and a spectroscopic method, and more particularly to a Fourier transform spectrometer and a Fourier transform spectroscopic method.

The spectrometer is a device that measures the spectrum of the light to be measured, one of which is an interferometer that measures the interference light of the light to be measured, and Fourier-transforms the measurement result, thereby measuring the light to be measured. There is a Fourier transform spectrometer that obtains a spectrum. This Fourier transform type spectrometer is disclosed in Patent Document 1, for example.

The Fourier spectrometer disclosed in Patent Document 1 includes an interferometer that emits interference light of light to be measured emitted from a light source, a photodetector that detects the light intensity of interference light emitted from the interferometer, An analog-to-digital converter (AD converter) that converts the output of the photodetector from an analog signal to a digital signal, and a spectrum of the light to be measured is obtained by performing Fourier arithmetic processing on the output of the AD converter. And an arithmetic processing circuit. In such a Fourier spectrometer, the output of the interferometer (the output of the photodetector, the output of the AD converter) is such that light of a plurality of wavelengths emitted from the light source is collectively interfered by the interferometer. This combined waveform is called an interferogram, and has a profile having 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. In order not to saturate the AD converter with this center burst, if the full span of the AD converter is set to the center burst, the measurement result includes a large noise of the AD converter. Therefore, the Fourier spectrometer disclosed in Patent Document 1 detects minute signals near zero with one AD converter, while detecting fluctuations in the center burst portion with other AD converters as non-saturated signals. The noise of the AD converter is reduced.

As described above, the Fourier spectrometer disclosed in Patent Document 1 requires two AD converters, and it is also necessary to match the timing when synthesizing the outputs.

JP 09-005160 A

The present invention has been made in view of the above-described circumstances, and its purpose is a Fourier that can detect even a minute signal near the zero level of an interferogram with a higher resolution even with a single AD converter. A conversion spectrometer and a Fourier transform spectroscopy method are provided.

In the Fourier transform spectrometer and the Fourier transform spectroscopic method according to the present invention, two first and second optical paths formed by a plurality of optical elements are provided between the incident position of the light to be measured and the interference position. In the case where each of the two first and second optical paths is formed of the same medium, the plurality of optical elements is configured such that the optical path difference between the two first and second optical paths is zero. A phase difference interferometer having a phase difference between the optical paths in the arrangement state where is arranged. Since the Fourier transform spectrometer and the Fourier transform spectroscopic method having such a configuration use a phase difference interferometer, the amplitude thereof is larger than that of an interferogram obtained by an interferometer equipped with a conventional phase compensator. Since the height (level) becomes small, even a single AD converter can detect a minute signal near the zero level of the interferogram with higher resolution.

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 figure which shows the spectrum of the laser beam radiated | emitted from the light source for position measurement in the Fourier-transform-type spectrometer of embodiment. It is a circuit diagram which shows the structure of the envelope detection part in the Fourier-transform-type spectrometer of embodiment. It is a figure for demonstrating the structure of the interferometer in the Fourier-transform-type spectrometer of embodiment, the waveform (interferogram) of the interference light of to-be-measured light, and the waveform of the interference light of the laser beam of the position measurement light source. As an example, it is a figure which shows the waveform (interferogram) of the interference light of the to-be-measured light measured. As an example, it is a figure which shows the waveform of the interference light of the laser beam of the measured position measurement light source. It is a figure for demonstrating the structure of the Michelson interferometer in the conventional Fourier-transform-type spectrometer, the waveform (interferogram) of the interference light of the to-be-measured light, and the waveform of the interference light of the laser beam of the position measurement light source. It is a figure which shows the waveform (interferogram) of the interference light of the to-be-measured light as a prior art example. It is a figure which shows the interference waveform of the laser beam of the light source for position measurement measured as a prior art example. It is a figure which shows the phase shift which arises with a semi-transparent mirror. It is a figure which shows the phase in the case of carrying out phase compensation of the phase shift which arises with a semi-transparent mirror. It is a figure which shows the relationship between an interferogram and a window function. The figure for demonstrating the structure of the interferometer of the 2nd aspect in the Fourier-transform-type spectrometer of embodiment, the waveform (interferogram) of the interference light of a to-be-measured light, and the waveform of the interference light of the laser beam of a position measurement light source It is. It is a figure which shows the structure of the interferometer of the 3rd aspect in the Fourier-transform-type spectrometer of embodiment. It is a figure for demonstrating the method of the 2nd aspect which calculates | requires the position of a center burst based on the envelope in the interference light of a laser beam. It is a figure for demonstrating the method of the 3rd aspect which calculates | requires the position of a center burst based on the envelope in the interference light of a laser beam.

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 showing a configuration of a Fourier transform spectrometer in 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 diagram illustrating a spectrum of laser light emitted from the position measurement light source in the Fourier transform spectrometer according to the embodiment. The horizontal axis in FIG. 3 is the wave number (1 / wavelength), and the vertical axis is the magnitude of the amplitude. FIG. 4 is a circuit diagram illustrating a configuration of an envelope detection unit in the Fourier transform spectrometer according to the embodiment.

The Fourier transform spectrometer D according to the embodiment is a device that measures the spectrum of the light to be measured as a measurement target, measures the light to be measured with an interferometer, and the waveform of the interference light of the measured light to be measured. This is a device for obtaining a spectrum of light to be measured by Fourier transforming (interferogram). For example, as shown in FIGS. 1 and 2, such a Fourier transform spectrometer D receives light (measurement light) emitted from the measurement target object SM and emits interference light of the measurement light. The interferometer 11 that receives the interference light of the light to be measured obtained by the interferometer 11, and an electric signal of the waveform of the interference light of the light to be measured by photoelectric conversion (represents a change in light intensity in the interference light of the light to be measured) A light reception processing unit 20 that outputs an electrical signal), a position detection processing unit 30 that detects the position of the movable mirror 115 of the interferometer 11, a control calculation unit 41, an input unit 42, and an output unit 43. . The measurement object SM may be a light source that emits light by itself, and is irradiated with light emitted from another light source, and radiates light by reflecting, transmitting, or re-radiating the light (for example, fluorescence emission). You may do.

The interferometer 11 receives measurement light to be measured, branches the incident measurement light into two first and second measurement lights, and the branched first and second measurement lights. Each travels (propagates) in the first and second optical paths, which are two different paths, and merges again. From this branch point (branch position), a merge point (merging position, interference position). If there is an optical path difference between the first and second optical paths until then, 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, beam splitter) 112 as a plurality of optical elements, a fixed mirror 114, and a moving mirror 115 that moves in the optical axis direction. 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.

Note that the movable mirror 115 may preferably have a configuration in which the reflecting surface moves in translation using a parallel leaf spring. The movable mirror 115 having a parallel leaf spring structure includes an actuator (not shown) that gives a driving force to move the mirror surface from the outside, and a driving signal that resonates the reflecting surface (mirror surface) is given to the actuator. In the movable mirror 115 using the translational property of such a parallel leaf spring structure, the position of the movable mirror 115 when not driven (when stationary) is the center of movement (vibration) and becomes the reference position when stationary. The reference position of the optical path length branched to the movable mirror 115 side. Therefore, the position of the reflecting surface when the parallel leaf spring is stationary is “the optical path length on the fixed mirror 114 side and the optical path length on the movable mirror 115 side are formed of the same medium. This is a reference for the optical path on the movable mirror 115 side when the optical element is arranged so that the optical path difference is zero (0).

In this embodiment, the interferometer 11 is arranged on the transmission side of the semi-transparent mirror 112 that has passed through 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 first retardation plate 113 is further provided. That is, in the present embodiment, the second measured light that has passed through the semi-transparent mirror 112 is incident on the movable mirror 115 via the first phase difference plate 113, and the second measured light that is reflected by the movable mirror 115 is The light enters the semi-transparent mirror 112 again through the first retardation plate 113. The first phase difference plate 113 is an isotropic phase plate, and the first phase difference plate 113 with respect to the phase of light traveling in the vacuum or in air for the same distance as the thickness of the first phase difference plate 113. This causes a shift in the phase of the light traveling inside. The later-described phase compensation plate CP, second phase difference plate 117, and transparent substrate of the semi-transparent mirror 112 also function in the same manner.

Furthermore, in this embodiment, in order to make the light to be measured radiated from the measurement target object SM incident on the semi-transparent mirror 112 as parallel light, the incident optical is placed at an appropriate position between the measurement target object SM and the semi-transparent mirror 112. For example, a biconvex collimator lens 111 is disposed as a system, and the first and second light receiving units collect the interference light of the light to be measured generated by the first and second light beams to be combined and interfered by the semi-transparent mirror 112. For example, a biconvex condensing lens 116 is disposed as an emission optical system at an appropriate position between the semi-transparent mirror 112 and the first light receiving unit 21 in order to enter the lens 21.

Returning to FIG. 1, the light reception processing unit 20 includes, for example, a first light reception unit 21, an amplification unit 22, and an analog-digital conversion unit (hereinafter referred to as “AD conversion unit”) 23. . The first light receiving unit 21 is a circuit that outputs an electric signal corresponding to the light intensity of the interference light of the light to be measured by receiving and photoelectrically converting the interference light of the light to be measured obtained by the interferometer 11. . The first light receiving unit 21 is, for example, an infrared sensor that includes an InGaAs photodiode and its peripheral circuits. 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 is executed at the zero cross timing input from the zero cross detector 37 described later.

Further, the position detection processing unit 30 includes, for example, a position measurement light source 31, a second light receiving unit 36, a zero cross detection unit 37, and an envelope detection unit 38. Then, the position detection processing unit 30 obtains the interference light of the laser light emitted from the position measurement light source 31 with the interferometer 11, as shown in FIG. 2, a collimator lens 32, a semi-transparent mirror 33, A semi-transparent mirror 34 and a condenser lens 35 are further provided.

The position measurement light source 31 is a light source device that emits laser light having a predetermined line width set in advance. The position measuring light source 31 includes, for example, a semiconductor laser that emits laser light having a predetermined line width. Further, for example, the position measuring light source 31 includes a laser device that emits monochromatic laser light, and a high-frequency superimposing device that superimposes the monochromatic laser light emitted from the laser device at a high frequency. A laser beam having a predetermined line width is emitted. The predetermined line width is a wavelength width (frequency width) such that the amplitude of the interference light of the laser light obtained by the interferometer 11 changes according to the movement of the movable mirror 115 of the interferometer 11. When the laser light is a bright line, the amplitude of the interference light of the laser light does not change due to the movement of the movable mirror 115 of the interferometer 11. As an example of the laser beam having such a predetermined line width, as shown in FIG. 3, a Gaussian profile having a full width at half maximum (FWHM) of 2.3 / cm with respect to a center wave number of 15151.52 / cm. have.

In FIG. 2, a collimator lens 32 and a half mirror (half mirror, beam splitter) 33 are incident optical systems for causing the laser light emitted from the position measuring light source 31 to enter the interferometer 11 with parallel light. The semi-transparent mirror 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, for example, a biconvex lens, and is appropriately set so that the laser light emitted from the position measurement light source 31 is incident on the semi-transparent mirror 33 arranged in this manner at an incident angle of 45 degrees. Placed in position. The semi-transparent mirror (half mirror, beam splitter) 34 and the condenser lens 35 are an emission optical system for taking out the interference light of the laser beam generated by the interferometer 11 from the interferometer 11. The semi-transparent mirror 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 semi-transparent mirror 34 arranged in this manner and enters the second light receiving unit 36. Let The semi-transparent mirror 33 may be a dichroic mirror that reflects laser light and transmits measured light. The semi-transparent mirror 34 reflects interference light of laser light and transmits interference light of measured light. A dichroic mirror may be used.

When the optical elements such as the collimator lens 32, the

semi-transparent mirrors

33 and 34, and the condenser lens 35 are arranged in this way, the laser light having the predetermined line width emitted from the position measuring light source 31 is collimated. The light beam 32 is converted into parallel light, and its optical path is bent by about 90 degrees by the semi-transparent mirror 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. The interference light of the laser light is bent about 90 degrees by the semi-transparent mirror 34, taken out from the interferometer 11, collected 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 the interference light of the laser light obtained by the interferometer 11 and photoelectrically converts it, thereby outputting an electric signal corresponding to the light intensity of the interference light of the laser light. It is a circuit to do. 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 each of the zero cross detection unit 37 and the envelope detection unit 38.

The zero-cross detection unit 37 is a circuit that detects a 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. 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 37 detects the zero cross of the electrical signal that repeats the strength in a sine wave form. The zero-cross detection unit 37 outputs the detected zero-cross timing to the AD conversion unit 23, and the AD conversion unit 23 outputs the interference light of the measured light input from the first light receiving unit 21 at the zero-cross timing. An electrical signal corresponding to the light intensity is sampled and AD converted.

The envelope detector 38 is a circuit that detects an envelope of an electric signal input from the second light receiver 36 and corresponding to the light intensity of the interference light of the laser beam. The envelope detector 38 can employ various circuit configurations. For example, as shown in FIG. 4, the envelope detector 38 is connected in series to the diode D by being connected to the diode D and the cathode terminal of the diode D. The resistor element R is connected to the resistor element R, and the capacitor C is connected in parallel to the resistor element R. Both ends of the series-connected diode D and the resistor element R are input ends, and both ends of the resistor element R are The output end. The envelope detector 38 can detect the envelope with such a simple circuit configuration. The envelope detection unit 38 outputs an envelope of an electric signal corresponding to the detected light intensity of the interference light of the laser beam to the control calculation unit 41.

The control calculation unit 41 controls each part of the Fourier transform spectrometer D according to the function of each part in order to obtain the spectrum of the light to be measured. The control calculation unit 41 is, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) or an EEPROM (Electrically) that stores various programs executed by the CPU, data necessary for the execution, and the like in advance.
The microcomputer includes a nonvolatile memory element such as an Erasable Programmable Read Only Memory), a volatile memory element such as a RAM (Random Access Memory) serving as a so-called working memory of the CPU, and a peripheral circuit thereof. The control calculation unit 41 is functionally configured with a spectrum calculation unit 411 and a center burst position calculation unit 412 by executing a program.

The center burst position calculation unit 412 detects the position of the center burst in the interferogram when the initial phase difference of each wavelength component of the light under measurement is zero. More specifically, in this embodiment, the center burst position calculation unit 412 detects a position that gives the maximum value of the envelope detected by the envelope detection unit 38 as the position of the center burst. As described above, in the present embodiment, the position of the center burst detects the envelope of the light intensity in the interference light of the laser light obtained by making the laser light having a predetermined line width enter the interferometer 11, It is obtained by detecting the position giving the maximum value of the detected envelope.

The spectrum calculation unit 411 performs Fourier transform on the interferogram of the light to be measured obtained by the interferometer 11 based on the position of the center burst detected by the center burst position calculation unit 412, thereby A spectrum is obtained.

The input unit 42 measures, for example, various commands such as a command for instructing the start of measurement, and a spectrum such as an input of an identifier in the light source SM to be measured and a selection input of a window function used at the time of Fourier transform. Is a device that inputs various data necessary for the Fourier transform 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 predicted by the Fourier transform spectrometer D. For example, the output unit 43 includes a CRT display, an LCD, an organic EL display, and the like. A display device such as a plasma display or a printing device such as a printer.

Next, the operation of this embodiment will be described. FIG. 5 is a diagram for explaining the configuration of the interferometer in the Fourier transform spectrometer of the embodiment, the waveform of the interference light of the light under measurement (interferogram), and the waveform of the interference light of the laser light of the position measurement light source. It is. FIG. 5A shows the configuration of the interferometer in the Fourier transform spectrometer of the embodiment, and FIG. 5B shows the waveform (interferogram) of the interference light of the measured light schematically drawn. FIG. 5C shows a waveform of interference light of the laser light of the position measurement light source schematically drawn. FIG. 6 is a diagram illustrating a waveform (interferogram) of interference light of actually measured light as an example. FIG. 6A shows the whole, FIG. 6B shows the vicinity of the zero level, and FIG. 6C shows the vicinity of the center burst. FIG. 7 is a diagram illustrating an interference waveform of laser light from a position measurement light source that is actually measured. FIG. 7A shows the whole, FIG. 7B shows the vicinity of the end, and FIG. 7C shows the vicinity of the maximum value. FIG. 8 is a diagram for explaining the configuration of the Michelson interferometer in the conventional Fourier transform spectrometer, the waveform of the interference light of the light under measurement (interferogram), and the waveform of the interference light of the laser light of the position measurement light source. FIG. FIG. 8A shows the configuration of a Michelson interferometer in the case of including a phase compensation phase difference plate in a conventional Fourier transform spectrometer, and FIG. 8B shows the phase compensation phase difference plate. FIG. 8C schematically shows the interference light waveform (interferogram) of the measured light, and FIG. 8D shows the configuration of the Michelson interferometer in the case where it is not provided. The waveform of the interference light of the laser beam of the light source for position drawing drawn typically is shown. FIG. 9 is a diagram illustrating a waveform (interferogram) of interference light of actually measured light as a conventional example. FIG. 9A shows the whole, FIG. 9B shows the vicinity of the zero level, and FIG. 9C shows the vicinity of the center burst. FIG. 10 is a diagram showing an actually measured interference waveform of laser light from a position measuring light source as a conventional example. 10A shows the whole, FIG. 10B shows the vicinity of the end, and FIG. 10C shows the vicinity of the maximum value. FIG. 11 is a diagram showing a phase shift that occurs in the semi-transparent mirror. FIG. 12 is a diagram showing the phase when the phase shift caused by the semi-transparent mirror is compensated. The horizontal axis in FIGS. 11 and 12 indicates the wavelength expressed in nm, and the vertical axis indicates the phase expressed in degrees. FIG. 13 is a diagram illustrating the relationship between the interferogram and the window function. The horizontal axis in FIG. 13 indicates the optical path difference, and the vertical axis indicates the amplitude.

When the measurement is started, the Fourier transform spectrometer D takes in the measurement light emitted from the measurement object SM. The measured light enters the interferometer 11 and is received by the first light receiving unit 21 as interference light of the measured light. 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 via the beam splitter 33 to be 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 enters the fixed mirror 114, is reflected by the fixed mirror 114, and returns to the semi-transparent mirror 112 again by following the optical path that has come. 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 via the first phase difference plate 113, reflected by the movable mirror 115, and traces the optical path that has come reversely. 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. As described above, the Fourier transform spectrometer D has at least one optical path so that the difference in the number of refraction regions accompanied by the optical path extension is 2 or more in each light passing through the two first and second optical paths. A first retardation plate 113, which is an optical element made of a transparent substrate, is provided therein (see FIG. 5). Here, the refracting region accompanied by the optical path extension is a region in which the optical path length is increased by refraction compared to the optical path length when the light is not refracted between two parallel planes. For example, in FIG. 5A, in the optical path that passes through the semi-transparent mirror 112 and reaches the movable mirror 115, the optical path inside the transparent member that constitutes the semi-transparent mirror 112 is accompanied by the extension of the optical path. The internal region of the transparent member corresponds to a refractive region, and the optical path inside the transparent member constituting the first retardation plate 113 is accompanied by an optical path extension, and the inside of the transparent member constituting the first retardation plate 113 The region corresponds to the refractive region. In FIG. 5A, the difference in the number of refractive regions between the optical path from the incident point of the semi-transparent mirror 112 to the movable mirror 115 and the optical path from the incident point to the fixed mirror 114 is 2, and the optical path difference is It will be set larger. 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 Fourier transform spectrometer D also captures laser light having a predetermined line width emitted from the position measurement light source 31. This laser light is incident on the interferometer 11 via the beam splitter 33, interferes with the interferometer 11 in the same manner as described above, and is received by the second light receiving unit 36 via the beam splitter 34 as interference light of the laser light. Is done. 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 each of the zero cross detection unit 37 and the envelope detection unit 38. To do. The zero cross detection unit 37 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 under the control of the control calculation unit 41.

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 37, and converts the electrical signal from an analog signal to a digital signal. A / D conversion is performed, and the electric signal of the digital signal subjected to the AD conversion is output to the spectrum calculation unit 411 of the control calculation unit 41.

By operating in this way, an interferogram as shown in FIG. 5B and FIG. 6 is input from the AD conversion unit 23 to the spectrum calculation unit 411 of the control calculation unit 41.

Here, the interferogram generated by the Fourier transform spectrometer D in the present embodiment will be described in comparison with the interferogram generated by the conventional phase-compensated Fourier transform spectrometer.

First, the phase compensation of a conventional Fourier transform spectrometer will be described. As shown in FIG. 8B, the Michelson interferometer without the phase compensation plate for phase compensation includes a semi-transparent mirror 112, a fixed mirror 114, and a moving mirror 115 that moves in the optical axis direction. The fixed mirror 114 and the movable mirror 115 are arranged so that their optical axes are orthogonal to each other, and the semi-transparent mirror 112 intersects each of these optical axes at an angle of 45 degrees and at the intersection of these optical axes. It arrange | positions so that a semi-transparent mirror surface may be located. In such a Michelson interferometer, the light to be measured is reflected by the semi-transparent mirror 112 and incident on the fixed mirror 114, reflected by the fixed mirror 114, returned to the semi-transparent mirror 112, and transmitted through the semi-transparent mirror 112. The optical path (semi-transparent mirror 112 → fixed mirror 114 → semi-transparent mirror 112) and the semi-transparent mirror 112 are incident on the movable mirror 115, reflected by the movable mirror 115, returned to the semi-transparent mirror 112, and reflected by the semi-transparent mirror 112. Two optical paths of the second optical path (semi-transparent mirror 112 → moving mirror 115 → semi-transparent mirror 112) are formed.

Here, when each of the two first and second optical paths is formed of the same medium, the optical path difference between the two first and second optical paths is zero. In the arrangement state in which each of the semi-transparent mirror 112, the fixed mirror 114, and the movable mirror 115 is arranged, the first object that is branched by the semi-transparent mirror 112 and travels (propagates) in the first optical path at the merging position (interference position). There is no phase difference between the measurement light and the second light to be measured branched by the semi-transparent mirror 112 and traveling on the second optical path. The case where each of these two first and second optical paths is formed of the same medium is, for example, the case where the first and second optical paths are formed of the same material as the transparent substrate of the semi-transparent mirror 112. Or, for example, when the semi-transparent mirror 112, the fixed mirror 114, and the movable mirror 115 are each disposed in a vacuum or in a gas, and the semi-transparent mirror 112 is formed only by the semi-transparent mirror surface. Note that the semi-transparent mirror 112 of the semi-transparent mirror is usually of a negligible thickness.

Actually, as shown in FIG. 8B, the semi-transparent mirror 112 includes a transparent substrate formed of a material transparent to the wavelength of the light to be measured or the laser beam, such as glass or resin, and the transparent substrate. For example, a semi-transparent surface such as a metal thin film or a dielectric multilayer film. For this reason, as shown in FIG. 8B, at the time of merging (interference), the first measured light in the first optical path does not pass through the transparent substrate of the semi-transparent mirror 112, but the second in the second optical path. The light to be measured passes through the transparent substrate of the semi-transparent mirror 112 twice. That is, in FIG. 8B, there is no refraction area in the first optical path toward the fixed mirror 114, and one refraction area is disposed in the second optical path toward the movable mirror. Therefore, the difference in the refractive area between these two optical paths is “1”. Accordingly, each of the two first and second optical paths formed by the semi-transparent mirror 112, the fixed mirror 114, and the movable mirror 115 is formed of the same medium between the incident position of the light to be measured and the interference position. Even in the arrangement state in which the semi-transparent mirror 112, the fixed mirror 114, and the movable mirror 115 are arranged so that the optical path difference between the two optical paths becomes zero in the case where the first optical path and the second optical path are The phase difference from the optical path does not become zero due to the refractive index of the transparent substrate. The amount of phase shift caused by the transparent substrate of the semi-transparent mirror 112 has a wavelength dependency as shown in FIG. 11, for example, because the refractive index has a wavelength dependency. is doing.

For this reason, in the conventional interferometer, as shown in FIG. 8A, when each of the two first and second optical paths is formed of the same medium, these two In the arrangement state in which each of the semi-transparent mirror 112, the fixed mirror 114, and the movable mirror 115 is arranged so that the optical path difference between the first and second optical paths becomes zero, the semi-transparent mirror is at the joining position (interference position). The phase difference actually generated between the first measured light branched at 112 and traveling (propagating) in the first optical path and the second measured light branched at the semi-transparent mirror 112 and traveled on the second optical path In order to compensate for this, a phase compensation plate CP having the same phase characteristics (refractive index characteristics) as the transparent substrate of the semi-transparent mirror 112 is disposed between the semi-transparent mirror 112 and the fixed mirror 114. For example, such a phase compensation plate CP is the transparent substrate itself of the semi-transparent mirror 112 (of course, there is no semi-transparent mirror surface). By disposing such a phase compensation plate CP, the phase difference between the first and second optical paths is eliminated as shown in FIG. That is, in FIG. 8A, a refractive region is provided in each of the two optical paths, and the difference in the number of refractive regions is zero. When such a phase compensated interferometer is used, the interferogram in the interference light of the light to be measured has an initial phase difference of each wavelength component of the light to be measured, which is shown in FIG. 8C or FIG. As described above, the profile has a large center burst and a small side lobe. For this reason, the position of the center burst in the interferogram when the initial phase difference of each wavelength component of the light to be measured is zero is relatively clear. The initial phase is a phase at a position where the optical path difference is 0 (center burst position).

On the other hand, the interferogram by the interferometer 11 in the present embodiment does not include the above-described phase compensation plate CP that is conventionally used, and further includes the phase difference plate 113 only in the second optical path. That is, the interferometer 11 in the present embodiment is formed by a plurality of optical elements (semi-transparent mirror 112, fixed mirror 114, and movable mirror 115 in the example shown in FIG. 2) between the incident position of the light to be measured and the interference position. Two first and second optical paths, and when each of the two first and second optical paths is formed of the same medium, between the two first and second optical paths. The phase difference interferometer has a phase difference between the optical paths in the arrangement state in which the plurality of optical elements are arranged so that the optical path difference becomes zero. In other words, the phase difference interferometer is in an arrangement state in which the movable mirror 114 is located at the center burst position in the case where the phase compensation is performed as in the case of the interferometer having the conventional phase compensation plate CP. There is a phase difference between the two first and second optical paths. Thus, in the present embodiment, the interferometer 11 is a phase difference interferometer, and as an example, as can be seen by comparing FIG. 6 and FIG. 9, the interferometer 11 is an interferometer equipped with a conventional phase compensator CP. Compared to the interferogram, the magnitude (level) of the amplitude is small. For example, as shown in FIG. 9C, the maximum amplitude Y in the interferogram by the interferometer provided with the conventional phase compensator CP is about 3200. However, according to the interferometer 11 of this embodiment. The magnitude X of the maximum amplitude in the interferogram is about 1400 as shown in FIG. 6C (X <Y).

Therefore, when these interferograms are AD-converted by an AD converter having the same number of bits Z, the A / D count assigned to one unit amplitude level is more conventional in the Fourier transform spectrometer D of the present embodiment. More than the conventional Fourier transform type spectrometer using an interferometer equipped with a phase compensation plate CP. That is, in the Fourier transform spectrometer using the interferometer having the conventional conventional phase compensator CP, X is the maximum amplitude at one or more peaks of the interferogram in the Fourier transform spectrometer D of the present embodiment. When the maximum amplitude at one or more peaks of the interferogram is Y, when X <Y and when the number of bits of the AD converter is Z, the A / D count assigned to one unit amplitude level 2 ^Z / X> 2 ^Z / Y, and the number of Fourier transform spectrometers D of this embodiment is larger than that of a conventional Fourier transform spectrometer using an interferometer equipped with a conventional phase compensation plate CP. Therefore, the Fourier transform spectrometer D of the present embodiment is relatively more relative to the electrical signal near the zero level than the conventional Fourier transform spectrometer using the interferometer having the phase compensation plate CP. Many A / D counts are assigned (2 ^Z / X> 2 ^Z / Y). Therefore, the Fourier transform spectrometer D of the present embodiment can detect a minute signal near the zero level of the interferogram with higher resolution even with a single AD converter.

On the other hand, in the Fourier transform type spectrometer D of the present embodiment, as described above, a phase difference interferometer is used as the interferometer 11, so, for example, as shown in FIG. The position of the burst is unclear. Therefore, the Fourier transform spectrometer D of the present embodiment obtains the position of the center burst from the envelope in the interference light of the laser beam having a predetermined line width.

In a conventional Fourier transform spectrometer, monochromatic laser light (monochromatic laser light) is used to detect the moving position of the moving mirror in the interferometer and obtain AD conversion sampling timing. More specifically, the monochromatic laser light is incident on the interferometer, and the light intensity in the interference light of the monochromatic laser light is detected by receiving the interference light of the monochromatic laser light generated by the interferometer. As shown in FIG. 10, the light intensity of the interference light of the monochromatic laser light repeatedly increases and decreases in a sine wave shape according to the movement of the movable mirror. Therefore, the sampling timing of the AD conversion is obtained by detecting this zero cross timing. ing. As shown in FIGS. 10A, 10B, and 10C, the light intensity of the interference light of the monochromatic laser light has a substantially constant amplitude regardless of the position of the optical path difference 0 or the position of the sideband. The position of the optical path difference 0 corresponds to the position of the center burst in the interferogram when the initial phase difference of each wavelength component of the light under measurement is zero.

In the Fourier transform spectrometer D of the present embodiment, laser light having a predetermined line width is used instead of the monochromatic laser light. As shown in FIG. 7, the interference light of the laser light having such a predetermined line width is the same as that of the monochromatic laser light in the zero cross timing, but FIGS. 7A, 7B and 7C. ), The amplitude is the largest at the position where the optical path difference is 0, and the amplitude gradually decreases as the position approaches the sideband position. Therefore, the position of the center burst can be detected by detecting the envelope of the light intensity in the interference light of the laser light having a predetermined line width. More specifically, the envelope detection unit 38 envelope-detects an electric signal according to the light intensity in the interference light of the laser beam input from the second light receiving unit 36, and the result is a control calculation unit 41. To the center burst position calculation unit 412. The center burst position calculation unit 412 detects the maximum value of the envelope input from the envelope detection unit 38, and obtains the position that gives this maximum value as the position of the center burst. Then, the center burst position calculation unit 412 outputs the obtained center burst position to the spectrum calculation unit 411.

Through the above operation, the spectrum calculation unit 411 receives the interferogram of the light to be measured from the AD conversion unit 23 and the center burst position from the center burst position calculation unit 412. Then, the spectrum calculation unit 411 performs Fourier transform on the interferogram of the measured light based on the detected position of the center burst, and obtains the spectrum of the measured light. The obtained spectrum of the light to be measured is output to the output unit 43.

More specifically, first, in the interferogram F _m (x _i ), the optical path difference is x _i , the wave number is ν _j , the spectral amplitude of the wave number ν _j is B (ν _j ), and the optical path difference is 0. Where X is ₀ and the phase at the position of optical path difference 0 of wave number ν _j is φ (ν _j ). Note that m represents the measurement result of the mth measurement.

In the case where a sufficient result with little noise can be obtained by one measurement, one measurement may be performed, but usually, an integration (sum) of a plurality of measurement results is obtained, and noise is reduced. This integrated interferogram (integrated interferogram) F (x _i ) is expressed by Equation 2.

Then, the interferograms F _m (x _i ) and F (x _i ) represented by the formula 1 or the formula 2 are subjected to Fourier transform. When performing fast Fourier transform (FFT), generation of side lobes is prevented. In order to reduce the frequency, a window function A _window (x _i ) that is symmetrical about the position of the optical path difference 0 (center burst position) is multiplied as shown in FIG. And the amplitude | B _window (ν _j ) | of the spectrum of the light to be measured is obtained (formula 4). In the case, where,

Equations

3 and 4 is shown for the case of the interferogram F (x _i) of the formula 2, which is obtained once the measurement with less noise satisfactory results in the Instead of Formula 2, the interferogram F _m (x _i ) represented by Formula 1 may be used.

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

Through such calculation processing, the spectrum calculation unit 411 performs fast Fourier transform on the interferogram of the measured light obtained by the interferometer 11 based on the position of the center burst detected by the center burst position calculation unit 412. Thus, the spectrum of the light to be measured is obtained.

As described above, the Fourier transform spectrometer D according to the present embodiment is a phase difference interferometer having a phase difference even if the optical elements constituting the interferometer 11 are arranged at a virtual optical path difference of zero. Since the interference light of the measured light is generated by the interferometer 11, the maximum amplitude X at one or more peaks of the interferogram is generated by a normal interferometer that compensates for the phase difference. It becomes smaller than the maximum amplitude Y at one or more peaks of the interferogram corresponding to the interference light of the light to be measured (X <Y). Therefore, when an electric signal obtained by receiving the interference light is AD converted by a Z-bit AD converter, a relatively larger A / D count is assigned to the electric signal near zero level ( ^2Z / X> ^2Z / Y). Therefore, the Fourier transform type spectrometer D and the Fourier transform type spectroscopic method implemented in the present embodiment are very small in the vicinity of the zero level of the interferogram even when one AD converter is used. Can also be detected with higher resolution.

Further, since the Fourier transform spectrometer D of the present embodiment satisfies X <Y as described above, an operational amplifier with a relatively low slew rate (relatively slow tracking with respect to an input signal) is used as the amplifier of the amplification unit 22. Operational amplifier), and a low noise amplifier can be used. By using a low noise amplifier (LNA) as the amplifier of the amplifying unit 22, the Fourier transform spectrometer D of the present embodiment can improve the so-called SN ratio.

In addition, since the Fourier transform spectrometer D of the present embodiment further includes the first retardation plate 113 on the transmission side of the semi-transparent mirror 112, the phase difference between the first and second optical paths in the interferometer 11 is further increased. be able to. As a result, the Fourier transform spectrometer D of the present embodiment does not include the first phase difference plate 113 shown in FIG. 14A described later with the maximum amplitude X at one or more peaks of the interferogram. The interferogram can be made smaller than the interferogram obtained by the phase difference interferometer having only the phase difference generated on the transparent substrate of the semi-transparent mirror 112.

Further, the Fourier transform spectrometer D of the present embodiment detects the position of the center burst by detecting the envelope of the light intensity in the interference light of the laser light having a predetermined line width. As shown, the detection circuit can be configured with a simpler circuit configuration.

Further, in the Fourier transform spectrometer D of the present embodiment, the laser beam is a laser beam having a predetermined line width, and the configuration for detecting the position of the center burst is for detecting the position of the movable mirror 112. Some configurations are diverted. More specifically, the configuration from the position measurement light source 31 to the second light receiving unit 36 is shared, and the output of the second light receiving unit 36 is output to each of the zero cross detection unit 37 and the envelope detection unit 38. For this reason, the Fourier transform spectrometer D of the present embodiment can detect the position of the center burst with a smaller circuit configuration.

In the Fourier transform spectrometer D of the present embodiment, the position measuring light source 31 is a laser device that emits laser light having a predetermined line width by superimposing monochromatic laser light at a high frequency, or a predetermined line width. A semiconductor laser that emits a laser beam having the above is used. For this reason, in this embodiment, the position measuring light source 31 that emits the laser beam having the predetermined line width can be configured more simply.

FIG. 14 illustrates the configuration of the interferometer of the second aspect in the Fourier transform spectrometer of the embodiment, the waveform of the interference light of the light under measurement (interferogram), and the waveform of the interference light of the laser light of the position measurement light source. It is a figure for doing. FIG. 14A shows the configuration of the interferometer of the second aspect in the Fourier transform spectrometer of the embodiment, and FIG. 14B shows the waveform of the interference light of the light to be measured (interference) schematically drawn. 14C shows the waveform of the interference light of the laser beam of the position measurement light source schematically drawn. FIG. 15 is a diagram illustrating a configuration of the interferometer of the third aspect in the Fourier transform spectrometer of the embodiment.

In the above-described embodiment, as the phase difference interferometer, as shown in FIG. 2 and FIG. 5A, the interferometer 11 (first step) having the phase difference plate 113 between the semi-transparent mirror 112 and the movable mirror 115 is used. Although one mode of interferometer 11) is used, the present invention is not limited to this. For example, the second mode of interferometer 11a having the configuration shown in FIG. 14 or the third mode of interference having the configuration shown in FIG. It may be 11b in total.

More specifically, in the interferometer 11a of the second aspect, as described above, the semi-transparent mirror 112 itself causes a phase difference because the semi-transparent mirror 112 includes a transparent substrate, and therefore, as shown in FIG. In addition, the phase difference plate 113 in the interferometer 11 of the first aspect is omitted. Thus, in the Michelson interferometer having a very general configuration using the normal semi-transparent mirror 112 including the transparent substrate having the semi-transparent surface formed on one main surface, the normal use described above with reference to FIG. Since the phase compensation plate CP for performing the phase compensation is not provided, the phase difference interferometer can be easily configured. That is, the interferometer 11a according to the second aspect includes a semi-transparent mirror 112, a fixed mirror 114, and a moving mirror 115 that moves in the optical axis direction. The first measurement light reflected by the fixed mirror 114 and the second measurement light reflected by the movable mirror 115 are split by the semi-transparent mirror 112. A Michelson interferometer that interferes with each other, and the semi-transparent mirror 112 includes a transparent substrate and a semi-transparent surface formed on one main surface of the transparent substrate.

Such an interferometer 11a according to the second aspect also provides the same operational effects as the interferometer 11 according to the first aspect, but compares FIGS. 5 (B) and (C) with FIGS. 14 (B) and (C). As can be seen, in order to further include the phase difference plate 113, the interferometer 11 of the first aspect has a smaller maximum amplitude in the interference light of the measured light than the interferometer 11a of the second aspect, and the laser The amplitude change of the envelope in the interference light is large. For this reason, when comparing the interferometer 11 of the first aspect with the interferometer 11a of the second aspect, the interferometer 11 of the first aspect is more advantageous.

The interferometer 11b according to the third aspect includes a semi-transparent mirror 112, a fixed mirror 114, and a movable mirror 115 that moves in the optical axis direction. The first and second two light beams are measured by the semi-transparent mirror 112. The first measured light reflected by the fixed mirror 114 and the second measured light reflected by the movable mirror 115 are split into the measured light and incident on the fixed mirror 114 and the movable mirror 115, respectively. In the Michelson interferometer, the half mirror 112 includes a transparent substrate and a half mirror surface formed on one main surface of the transparent substrate. The interferometer 11b according to the third aspect reflects the reflected light of the half mirror 112 reflected by the half mirror 112 when the light to be measured is split into two first and second light beams to be measured by the half mirror 112. A second phase difference plate 117 is further provided on the side, and the second phase difference plate 117 generates a phase difference different from the phase difference generated in the semi-transparent mirror 112. The second retardation plate 117 is formed of a material having the same thickness as the transparent substrate of the semi-transparent mirror 112 and a different refractive index (refractive index characteristic) from the transparent substrate of the semi-transparent mirror 112, for example. The Further, for example, the second retardation plate 117 has a thickness different from that of the transparent substrate of the semi-transparent mirror 112 by a material (for example, the same material) having the same refractive index (refractive index characteristic) as that of the transparent substrate of the semi-transparent mirror 112. Is formed.

Since the interferometer 11b according to the third aspect further includes the second retardation plate 117 on the reflection side of the semi-transparent mirror 112, as compared with the interferometer 11a according to the second aspect having the configuration shown in FIG. The phase difference between the first and second optical paths can be further increased.

In the interferometer 11 of the first aspect configured as shown in FIGS. 2 and 5A, the interferometer 11c (not shown) of the fourth aspect may further include a second phase difference plate 117. .

FIG. 16 is a diagram for explaining a second mode method for obtaining the position of the center burst based on the envelope in the interference light of the laser beam. FIG. 16A shows the envelope, and FIG. 16B shows a differential waveform of the envelope. FIG. 17 is a diagram for explaining the method of the third aspect for obtaining the position of the center burst based on the envelope in the interference light of the laser light. The horizontal axis in FIGS. 16 and 17 indicates the optical path difference (position of the movable mirror 115), and these vertical axes indicate the levels.

In the above-described embodiment, the center burst position calculation unit 412 uses the envelope maximum value input from the envelope detection unit 38 as the amplitude value of the envelope according to the movement of the movable mirror 112 (change in optical path difference). For example, as shown in FIG. 16A, when the envelope is in the vicinity of the maximum value, the movement of the movable mirror 112 (change in optical path difference) may be detected. ), It is not easy to detect the point with high accuracy. For this reason, the center burst position calculation unit 412 determines the position that gives the maximum value of the envelope detected by the envelope detection unit 38 based on the difference information of the envelope detected by the envelope detection unit 38 as the position of the center burst. You may detect as.

More specifically, the center burst position calculation unit 412 obtains a difference between two points on the envelope at an appropriate interval. For example, when the difference between two points on the envelope is obtained with respect to the envelope shown in FIG. 16A, a difference graph shown in FIG. 16B is obtained as the difference information. In the difference graph, since the zero cross point at which the difference value changes from a positive value to a negative value corresponds to the position where the maximum value is given, the center burst position calculation unit 412 determines that the difference value is from the positive value in the difference graph. A zero cross point that turns to a negative value is obtained, and the zero cross point may be set as the center burst position.

Here, the larger the interval for obtaining the difference, the larger the difference value, and the zero cross point can be detected with higher accuracy. As a result, the position of the center burst can be detected with higher accuracy.

Further, when obtaining such a difference, the storage capacity of the storage element that stores the measurement result of the envelope is restricted, and the interval cannot be made too large, or the number of bits Z of the AD conversion unit 23 is small and the resolution is small. When the difference is not so large, the difference may have a stepped shape near the zero cross point as shown in FIG. In such a case, the position of the center burst may be obtained by linearly approximating the difference graph near the zero cross point by the least square method and obtaining the zero cross point of the approximate straight line.

By using such envelope difference information, the center burst position calculation unit 412 of the Fourier transform spectrometer D can detect the position giving the maximum value of the envelope more accurately. Even when it is difficult to distinguish the maximum value of the envelope because the change of the line is gradual, the position where the maximum value of the envelope is given can be detected.

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 includes two optical paths formed by a plurality of optical elements between a measurement light incident position and an interference position where the measurement target light is incident. When the plurality of optical elements are arranged so that the optical path difference between the two optical paths is zero when each of the two optical paths is formed of the same medium, the optical path is actually A phase difference interferometer having a phase difference therebetween, a center burst position detector for detecting a position of a center burst in an interferogram when the initial phase difference of each wavelength component of the light to be measured is zero, and An interferogram of the measured light obtained by the phase difference interferometer is Fourier-transformed based on the center burst position detected by the center burst position detector. And a spectrum calculating unit for obtaining the spectrum of said light to be measured by performing.

The Fourier transform type spectroscopic method according to another aspect includes two optical paths formed by a plurality of optical elements between the incident position of the measurement target light to be measured and the interference position. In the case where the plurality of optical elements are arranged such that the optical path difference between the two optical paths is zero when each of the optical paths is formed of the same medium, the phase difference between the optical paths is actually An interferogram acquisition step of obtaining an interferogram of the light to be measured by a phase difference interferometer having a center, and a center in the interferogram when the phase difference of each wavelength component of the light to be measured is zero A center burst position detecting step for detecting a burst position and an interferogram of the measured light obtained in the interferogram acquiring step And a spectrum calculation step of obtaining a spectrum of the light to be measured by performing a Fourier transform on the basis of the detected center burst position by the burst position detecting step.

In the Fourier transform spectrometer and the Fourier transform spectroscopic method having such a configuration, since the interference light of the light to be measured is generated by the phase difference interferometer, the maximum in one or a plurality of peaks of the interferogram is obtained. The amplitude X is smaller than the maximum amplitude Y at one or more peaks of the interferogram corresponding to the interference light of the measured light generated by the normal interferometer that compensates for the phase difference (X <Y). . For this reason, when using a Z-bit analog-digital converter (AD converter) that converts an electrical signal obtained by receiving interference light from an analog signal to a digital signal, Relatively more A / D counts are assigned (2 ^Z / X> 2 ^Z / Y). Therefore, when the AD converter is used, the Fourier transform spectrometer and the Fourier transform spectroscopic method having such a configuration have a higher minute signal near the zero level of the interferogram even with one AD converter. It can be detected with resolution.

According to another aspect, in the above-described Fourier transform spectrometer, the phase difference interferometer has a difference in the number of refraction regions accompanying optical path extension of 2 or more in each light passing through the two optical paths. Thus, an optical element made of a transparent substrate is provided in at least one of the optical paths.

A Fourier transform spectrometer having such a configuration can easily form a phase difference interferometer by disposing a transparent substrate in at least one optical path.

According to another aspect, in the Fourier transform spectrometer described above, the phase difference interferometer includes a semi-transparent mirror, a fixed mirror, and a movable mirror that moves in the optical axis direction as the plurality of optical elements. The measurement light is split into two first and second measurement light beams by the semi-transparent mirror, and is incident on the fixed mirror and the movable mirror, respectively, and is reflected by the fixed mirror. And a Michelson interferometer that causes the second measured light reflected by the movable mirror to interfere with each other by the semi-transparent mirror, wherein the semi-transparent mirror is formed on one main surface of the transparent substrate and the transparent substrate. A semi-transparent mirror surface.

The Fourier transform spectrometer having such a configuration performs phase compensation normally used in a general Michelson interferometer using a normal semi-transmission mirror including a transparent substrate having a semi-transmission surface formed on one main surface. Therefore, the phase difference interferometer can be easily configured.

Further, in another aspect, in the above-described Fourier transform spectrometer, when the light to be measured is branched into two first and second light to be measured by the semi-transparent mirror, the semi-transparent mirror is transmitted. A first retardation plate is further provided on the transmission side of the semi-transparent mirror.

Since the Fourier transform spectrometer having such a configuration further includes the first phase difference plate on the transmission side of the semi-transparent mirror, the phase difference between the optical paths in the phase difference interferometer can be further increased. .

According to another aspect, in the above-described Fourier transform spectrometer, when the light to be measured is branched into two first and second light to be measured by the semi-transparent mirror, the light is reflected by the semi-transparent mirror. A second retardation plate is further provided on the reflection side of the semi-transparent mirror, and the second retardation plate generates a phase difference different from the phase difference generated in the semi-transparent mirror.

Since the Fourier transform spectrometer having such a configuration further includes a second phase difference plate on the reflection side of the semi-transparent mirror, the phase difference between the optical paths in the phase difference interferometer can be further increased. .

According to another aspect, in the above-described Fourier transform spectrometer, the center burst position detection unit is obtained by causing a laser beam having a predetermined line width to enter the phase difference interferometer. An envelope of light intensity in the interference light of the laser beam is detected, and a position that gives a maximum value of the detected envelope is detected as the position of the center burst.

Since the Fourier transform spectrometer having such a configuration detects the position of the center burst by detecting the envelope of the light intensity in the interference light of the laser beam having a predetermined line width, it has a simpler circuit configuration. A detection circuit can be configured.

Further, in another aspect, in the above-described Fourier transform spectrometer, the interference light of the measurement light obtained by the phase difference interferometer is received, and the light intensity of the interference light of the measurement light is measured. A first light receiving unit for outputting, an analog-digital converting unit for converting the output of the first light receiving unit from an analog signal to a digital signal and outputting an interferogram of the light to be measured, and an output of the second light receiving unit to be described later And a zero-cross detector that outputs the detected zero-cross timing as a sampling timing to the analog-digital converter, and the center burst position detector includes a laser beam having a predetermined line width. A position measuring light source incident on the phase difference interferometer and the interference light of the laser beam obtained by the phase difference interferometer are received. Then, a second light receiving unit that outputs light intensity in the interference light of the laser light, an envelope detection unit that detects an envelope of the output of the second light receiving unit, and an envelope detected by the envelope detection unit And a center burst position calculation unit that detects a position that gives a local maximum value as the position of the center burst.

In the Michelson interferometer, in order to detect the position of the movable mirror, for example, interference light of a laser beam is used, and a zero cross timing in the interference light of the laser beam is set as a sampling timing. In the Fourier transform spectrometer having the above configuration, the laser beam is a laser beam having the predetermined line width, and a part for detecting the position of the movable mirror is used as a configuration for detecting the position of the center burst. The configuration of is diverted. For example, the configuration from the position measurement light source to the second light receiving unit is shared, and the output of the second light receiving unit is output to each of the zero cross detection unit and the envelope detection unit. For this reason, the Fourier transform spectrometer having the above configuration can detect the position of the center burst with a smaller circuit configuration.

In another aspect, in the above-described Fourier transform spectrometer, the position measurement light source is a laser device that emits laser light having the predetermined line width by superimposing monochromatic laser light at high frequency.

According to the above configuration, a position measurement light source that emits laser light having the predetermined line width is configured more simply.

In another aspect, in the above-described Fourier transform spectrometer, the position measurement light source is a semiconductor laser that emits laser light having the predetermined line width.

According to another aspect, in the above-described Fourier transform spectrometer, the center burst position calculation unit is detected by the envelope detection unit based on difference information of the envelope detected by the envelope detection unit. A position that gives the maximum value of the envelope is detected as the position of the center burst.

The Fourier transform spectrometer having such a configuration can detect the position where the maximum value of the envelope is given more accurately, and since the change of the envelope is gentle, the maximum value of the envelope is Even if it is difficult to distinguish, it is possible to detect the position that gives the maximum value of the envelope.

This application is based on Japanese Patent Application No. 2011-058635 filed on Mar. 17, 2011, the contents of which are included in this 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. It is interpreted that it is included in

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

Claims

A light to be measured to be measured is incident, and two optical paths formed by a plurality of optical elements are provided between an incident position of the measured light and an interference position, and each of the two optical paths is temporarily the same. In the case where the plurality of optical elements are arranged so that the optical path difference between the two optical paths is zero when the optical path is formed of the medium, a phase difference interferometer that actually has a phase difference between the optical paths. When,
A center burst position detector for detecting the position of the center burst in the interferogram when the initial phase difference of each wavelength component of the measured light is zero;
The spectrum of the measured light is obtained by performing Fourier transform on the interferogram of the measured light obtained by the phase difference interferometer based on the position of the center burst detected by the center burst position detector. A Fourier transform spectrometer characterized by comprising a required spectrum calculation unit.
The phase difference interferometer is an optical element composed of a transparent substrate in at least one of the optical paths so that the difference in the number of refractive regions accompanying the optical path extension is 2 or more in each light passing through the two optical paths. The Fourier transform spectrometer according to claim 1, comprising:
The phase difference interferometer includes a semi-transparent mirror, a fixed mirror, and a movable mirror that moves in an optical axis direction as the plurality of optical elements, and the first and second optical elements are measured by the semi-transparent mirror. The first measured light reflected by the fixed mirror and the second measured light reflected by the movable mirror are split into the second measured light and incident on the fixed mirror and the movable mirror, respectively. It is a Michelson interferometer which makes it mutually interfere with a transparent mirror, Comprising: The said semi-transparent mirror is provided with the transparent substrate and the semi-transparent surface formed in one main surface of the said transparent substrate. Fourier transform spectrometer.
In the case where the light to be measured is branched into two first and second light to be measured by the semi-transparent mirror, a first retardation plate disposed on the transmission side of the semi-transparent mirror that has passed through the semi-transparent mirror is further provided. The Fourier transform spectrometer according to claim 3.
In the case where the light to be measured is branched into two first and second light to be measured by the semi-transparent mirror, a second retardation plate disposed on the reflection side of the semi-transparent mirror reflected by the semi-transparent mirror is further provided. Prepared,
4. The Fourier transform spectrometer according to claim 3, wherein the second retardation plate generates a phase difference different from a phase difference generated in the semi-transparent mirror.
The center burst position detection unit detects an envelope of light intensity in the interference light of the laser light obtained by making a laser beam having a predetermined line width incident on the phase difference interferometer, and detects the detected envelope. The Fourier transform spectrometer according to claim 1, wherein a position giving a maximum value of the envelope is detected as the position of the center burst.
A first light receiving unit that receives the interference light of the measurement light obtained by the phase difference interferometer and outputs the light intensity in the interference light of the measurement light;
An analog-to-digital converter that converts an output of the first light receiving unit from an analog signal to a digital signal and outputs an interferogram of the light to be measured;
A zero-cross detector that detects a zero-cross of the output of the second light-receiving unit to be described later and outputs the detected zero-cross timing to the analog-digital converter as a sampling timing;
The center burst position detecting unit receives a laser beam having a predetermined line width on the phase difference interferometer, a position measurement light source, and the laser beam interference light obtained by the phase difference interferometer. Then, a second light receiving unit that outputs light intensity in the interference light of the laser light, an envelope detection unit that detects an envelope of the output of the second light receiving unit, and an envelope detected by the envelope detection unit The Fourier transform spectrometer according to claim 3, further comprising: a center burst position calculation unit that detects a position that gives a local maximum value as a position of the center burst.
The Fourier transform spectrometer according to claim 7, wherein the position measuring light source is a laser device that emits laser light having the predetermined line width by superimposing monochromatic laser light at high frequency.
The Fourier transform spectrometer according to claim 7, wherein the position measuring light source is a semiconductor laser that emits laser light having the predetermined line width.
The center burst position calculation unit detects a position that gives a maximum value of the envelope detected by the envelope detection unit as the position of the center burst based on difference information of the envelope detected by the envelope detection unit The Fourier transform spectrometer according to claim 7, wherein:
When two optical paths formed by a plurality of optical elements are provided between the incident position of the measured light to be measured and the interference position, and each of the two optical paths is temporarily formed of the same medium In the case where the plurality of optical elements are arranged so that the optical path difference between the two optical paths is zero, the measured light to be measured is actually measured by a phase difference interferometer having a phase difference between the optical paths. Interferogram acquisition step of obtaining an interferogram of,
A center burst position detecting step for detecting the position of the center burst in the interferogram when the phase difference of each wavelength component of the measured light is zero;
The spectrum of the light to be measured is obtained by performing Fourier transform on the interferogram of the light to be measured obtained in the interferogram acquisition step based on the position of the center burst detected by the center burst position detecting step. A Fourier transform type spectroscopic method, comprising: a required spectrum calculation step.