Laser interferometer and spectroscopic instrument

Abstract

To provide a laser interferometer capable of reducing the frequency of a signal subjected to arithmetic processing by a demodulator circuit to reduce cost for the demodulator circuit, and a spectroscopic instrument including the laser interferometer.SOLUTION: The laser interferometer comprises: an optical modulator adding a modulation signal to a laser beam using a vibration element; a light receiving element detecting a change in intensity of a laser beam including a sample signal and the modulation signal and outputting a laser beam receiving signal; a signal oscillation section generating a reference signal with first frequency using a vibration element as vibration source; and a demodulator circuit demodulating the sample signal from the laser beam receiving signal based on the reference signal. The demodulator circuit includes: a DC offset removal section removing offset; a first phase regulator adjusting the phase of the reference signal; a first multiplier multiplying the laser beam receiving signal and the reference signal; a first filter; a second multiplier multiplying a first multiplication signal and the reference signal; and a second filter; and a phase calculator calculating a phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser interferometer and a spectroscopic device. [Background technology]

[0002] Patent Document 1 discloses a laser Doppler measurement device for determining the movement of a moving object. The laser Doppler measurement device irradiates a laser beam onto the object and measures the movement of the object based on the scattered laser beam that has undergone a Doppler shift. Specifically, the amount of frequency shift of the laser beam is obtained by optical heterodyne interferometry, and the velocity and displacement of the moving object are calculated from this amount of shift.

[0003] The laser Doppler measurement device described in Patent Document 1 includes a frequency shifter-type optical modulator. This optical modulator includes a quartz crystal AT oscillator that vibrates in thickness shear mode and a diffraction grating that includes multiple grooves arranged in the direction of displacement of the oscillator. The diffraction grating has grooves in a direction that intersects with the vibration direction of the quartz crystal AT oscillator. When a laser beam is irradiated onto the diffraction grating, the laser beam is diffracted and the frequency of the laser beam is shifted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-165700 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, thickness-shear vibration has a high resonance frequency. As a result, the frequency of the modulated signal superimposed on the laser light by the optical modulator described in Patent Document 1 also becomes high. As a result, in the laser Doppler measurement device described in Patent Document 1, it becomes necessary to make the circuit that performs arithmetic processing on the modulated signal and the circuit that converts analog signals to digital signals compatible with high-frequency signals. As a result, these circuits become expensive.

[0006] Therefore, the realization of a laser interferometer that can reduce the frequency of the signal processed by the demodulation circuit and reduce the cost of the demodulation circuit has become an issue. [Means for solving the problem]

[0007] A laser interferometer according to an application example of the present invention includes: A laser interferometer that irradiates a target with laser light, receives the laser light that has passed through the target, and acquires a displacement of the target, a laser light source that emits the laser light; an optical modulator including a vibration element, the optical modulator adding a modulation signal to the laser light by using the vibration element; a light receiving element that detects a change in intensity of the laser light including the sample signal and the modulation signal added by the object, and outputs a laser light receiving signal; a signal oscillator that generates a reference signal of a first frequency using the vibration element as a source of vibration; a demodulation circuit that demodulates the sample signal from the laser beam reception signal based on the reference signal to obtain the displacement of the object; Equipped with The demodulation circuit a DC offset removal unit that removes an offset of a DC component of the laser beam reception signal; a first phase adjuster that adjusts the phase of the reference signal; a first multiplier that multiplies the laser beam reception signal output from the DC offset removal unit by the reference signal output from the first phase adjuster, and outputs a first multiplied signal; a first filter that removes high frequency components contained in the first multiplied signal; a second multiplier that multiplies the first multiplied signal by the reference signal output from the first phase adjuster and outputs a second multiplied signal; a second filter that removes high frequency components contained in the second multiplied signal; a phase calculator that calculates a phase derived from the object as the sample signal based on the signal output from the first filter and the signal output from the second filter; It has.

[0008] A spectroscopic device according to an application example of the present invention includes: a laser interferometer according to an application example of the present invention; a spectroscopic analysis unit having a spectroscopic optical system including a movable mirror and generating spectroscopic spectrum information derived from the sample; Equipped with the laser interferometer measures the displacement of the movable mirror; The spectroscopic analysis unit generates the spectroscopic information based on the measurement result of the displacement of the movable mirror by the laser interferometer. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram showing a laser interferometer according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of the interference optical system of FIG. [Figure 3] FIG. 3 is a perspective view showing an example of the configuration of the optical modulator shown in FIG. [Figure 4] 3 is a perspective view showing another example of the configuration of the optical modulator shown in FIG. 2. FIG. [Figure 5] 10 is a table showing coefficients included in a DC term and a term representing a harmonic component in a series representation of a laser beam reception signal. [Figure 6] 2 is a graph showing an example of frequency characteristics of the amount of phase delay of an AC component passing through the high-pass filter shown in FIG. 1. [Figure 7]7 is a graph showing the results of simulating the influence of a difference ψ1 in the amount of phase delay on the measurement accuracy of displacement in the design example shown in FIG. 6. [Figure 8] 7 is a graph showing the results of simulating the effect of a difference ψ1 in the amount of phase delay on the accuracy of displacement in the design example shown in FIG. 6. [Figure 9] This graph was created by calculating the frequency characteristics (bandwidth characteristics) of gain and the frequency characteristics (phase characteristics) of phase delay when the number of stages in a high-pass filter composed of an LCR circuit is changed to 1, 2, and 3. [Figure 10] FIG. 10 is a functional block diagram showing a laser interferometer according to a third embodiment. [Figure 11] FIG. 10 is a functional block diagram showing a laser interferometer according to a fourth embodiment. [Figure 12] FIG. 10 is a functional block diagram showing a spectroscopic device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser interferometer and a spectroscopic device according to the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0011] 1. First embodiment First, the laser interferometer according to the first embodiment will be described.

[0012] Fig. 1 is a functional block diagram showing a laser interferometer 1 according to the first embodiment. Fig. 2 is a schematic diagram showing the configuration of an interference optical system 50 shown in Fig. 1.

[0013] The laser interferometer 1 shown in FIG. 1 includes an interference optical system 50, a signal oscillator 51, and a demodulator circuit 52.

[0014] 2 splits the laser light emitted from the laser light source 2 and makes it incident on the object 14 and the optical modulator 12, respectively. The laser light returning from the object 14 and the optical modulator 12 is then mixed and received by the light receiving element 10. The light receiving element 10 detects a change in the intensity of the laser light, which includes a sample signal (such as phase information added to the laser light) added by the object 14 and a modulation signal (such as frequency information added to the laser light) added by the optical modulator 12, and outputs a laser light reception signal.

[0015] 1 includes a vibration element 30. The optical modulator 12 uses the vibration element 30 to add a modulation signal to the laser light.

[0016] Furthermore, the signal oscillator 51 shown in FIG. 1 generates a reference signal using the vibration element 30 as a vibration source.

[0017] 1 demodulates the laser beam reception signal into a sample signal based on the reference signal, thereby obtaining the displacement of the object 14 and the like.

[0018] 1.1.Interference optical system The interference optical system 50 shown in Fig. 2 is a Michelson type interference optical system, and includes a laser light source 2, a collimating lens 3, a beam splitter 4, a half-wave plate 6, a quarter-wave plate 7, a quarter-wave plate 8, an analyzer 9, and a light-receiving element 10.

[0019] The laser light source 2 emits an emission light L1 having a frequency f0. The light receiving element 10 converts the intensity of the received light into an electrical signal. The optical modulator 12 changes the frequency of the emission light L1 using the vibration element 30 to generate a reference light L2 containing a modulation signal (laser light containing a modulation signal). Meanwhile, the emission light L1 incident on the object 14 is reflected as an object light L3 containing a sample signal derived from the object 14 (laser light containing a sample signal).

[0020] The optical path connecting the optical splitter 4 and the laser light source 2 is referred to as optical path 18. The optical path connecting the optical splitter 4 and the optical modulator 12 is referred to as optical path 20. The optical path connecting the optical splitter 4 and the target 14 is referred to as optical path 22. The optical path connecting the optical splitter 4 and the light receiving element 10 is referred to as optical path 24. In this specification, the term "optical path" refers to a path along which light travels that is set between optical elements.

[0021] On the optical path 18, a half-wave plate 6 and a collimator lens 3 are arranged in this order from the optical splitter 4 side. On the optical path 20, a quarter-wave plate 8 is arranged. On the optical path 22, a quarter-wave plate 7 is arranged. On the optical path 24, an analyzer 9 is arranged.

[0022] Emitted light L1 from the laser light source 2 travels through an optical path 18 and is split into two by the optical splitter 4. One of the split emitted light L1, a first split light L1a, travels through an optical path 20 and is incident on the optical modulator 12. The other of the split emitted light L1, a second split light L1b, travels through an optical path 22 and is incident on the object 14. Reference light L2, which is frequency-shifted and generated by the optical modulator 12, travels through the optical paths 20 and 24 and is incident on the light-receiving element 10. Object light L3, which is generated by reflection on the object 14, travels through the optical paths 22 and 24 and is incident on the light-receiving element 10.

[0023] The laser interferometer 1 equipped with the interference optical system 50 described above uses optical heterodyne interferometry to obtain phase information of the object 14. Specifically, two beams of light (reference beam L2 and object beam L3) with slightly different frequencies are made to interfere with each other. Then, a demodulation circuit 52 extracts phase information from the intensity of the interference beam, and the displacement of the object 14 is obtained from the phase information. Optical heterodyne interferometry provides high robustness when extracting phase information from the interference beam, being less susceptible to the influence of external disturbances, particularly stray light with frequencies that become noise.

[0024] Each part of the interference optical system 50 will be further described below. Laser Light Source The laser light source 2 is a laser light source that emits coherent emitted light L1. A light source with a linewidth in the MHz range or less is preferably used as the laser light source 2. Specific examples include gas lasers such as He-Ne lasers, and semiconductor laser elements such as DFB-LDs (Distributed Feedback Laser Diodes), FBG-LDs (Fiber Bragg Grating Laser Diodes), VCSELs (Vertical Cavity Surface Emitting Lasers), and FP-LDs (Fabry-Perot Laser Diodes).

[0025] It is particularly preferable that the laser light source 2 is a semiconductor laser element, which makes it possible to particularly reduce the size of the laser light source 2. As a result, the laser interferometer 1 can be made smaller.

[0026] 1.1.2.Collimating lens The collimating lens 3 is an optical element, such as an aspherical lens, disposed between the laser light source 2 and the beam splitter 4. The collimating lens 3 collimates the light L1 emitted from the laser light source 2. If the light L1 emitted from the laser light source 2 is sufficiently collimated, for example, if a gas laser such as a He-Ne laser is used as the laser light source 2, the collimating lens 3 may be omitted.

[0027] The collimated emitted light L1 passes through the half-wave plate 6, where it is converted into linearly polarized light with an intensity ratio of P-polarized light to S-polarized light of, for example, 50:50, and enters the light splitter 4.

[0028] 1.1.3.Light splitter The light splitter 4 is a polarizing beam splitter that is placed between the laser light source 2 and the optical modulator 12, and between the laser light source 2 and the target 14. The light splitter 4 has the function of transmitting P-polarized light and reflecting S-polarized light. With this function, the light splitter 4 splits the output light L1 into a first divided light L1a that is a reflected light at the light splitter 4, and a second divided light L1b that is a transmitted light through the light splitter 4.

[0029] The first divided light L1a, which is S-polarized light reflected by the optical splitter 4, is converted into circularly polarized light by the quarter-wave plate 8 and is incident on the optical modulator 12. The first divided light L1a incident on the optical modulator 12 is M [Hz] and is reflected as reference light L2. Therefore, the reference light L2 has a modulation frequency f M That is, the frequency of the reference light L2 is f0+f M The reference light L2 is converted back to P-polarized light when it passes through the quarter-wave plate 8. The P-polarized light of the reference light L2 passes through the optical splitter 4 and the analyzer 9 and enters the light-receiving element 10.

[0030] The second divided light L1b, which is P-polarized light that has passed through the light splitter 4, is converted into circularly polarized light by the quarter-wave plate 7 and is incident on the moving object 14. The second divided light L1b that has entered the object 14 is D The object light L3 is subjected to a Doppler shift of f [Hz] and is reflected as the object light L3. D The frequency of the object beam L3 is f0-f D The object light L3 is converted back into S-polarized light when it passes through the quarter-wave plate 7. The S-polarized light of the object light L3 is reflected by the optical splitter 4, passes through the analyzer 9, and enters the light-receiving element 10.

[0031] Since the emitted light L1 has coherence, the reference light L2 and the object light L3 are incident on the light receiving element 10 as interference light.

[0032] 1.1.4.Analyzer Since the S-polarized light and the P-polarized light are orthogonal to each other and independent of each other, simply superimposing them does not produce beat noise due to interference. Therefore, the light waves of the superimposed S-polarized light and P-polarized light are passed through an analyzer 9 tilted at 45 degrees to both the S-polarized light and the P-polarized light. By using the analyzer 9, light with common components can be transmitted, causing interference. As a result, the reference light L2 and the object light L3 interfere with each other in the analyzer 9, and |f M -f D Interferometric light with a beat frequency of | is generated.

[0033] 1.1.5.Photodetector When the interference light enters the light-receiving element 10, the light-receiving element 10 outputs a photocurrent (laser light reception signal) corresponding to the intensity of the interference light. By demodulating this laser light reception signal into a sample signal using a method described below, the movement of the object 14, i.e., its displacement and velocity, can ultimately be determined. The light-receiving element 10 may be, for example, a photodiode. Note that the light received by the light-receiving element 10 is not limited to the interference light described above, as long as it is laser light emitted from the laser light source 2, the frequency and phase of which are modulated by the optical modulator 12 and the object 14, resulting in a superimposed modulation signal and sample signal. Furthermore, in this specification, "demodulating the sample signal from the laser light reception signal" refers to extracting the sample signal by performing various calculations on the laser light reception signal.

[0034] 1.2.Optical Modulator The optical modulator 12 shown in FIG. 1 includes a vibration element 30. As shown in FIG. 2, the optical modulator 12 modulates the frequency of the first divided light L1a using the vibration element 30. This configuration allows the optical modulator 12 to be compact, lightweight, and consume less power. Furthermore, the oscillation of the vibration element 30 serves as the source oscillation when the signal oscillator 51 generates a reference signal. Therefore, the modulation signal added to the reference light L2 by the vibration element 30 and the reference signal output from the signal oscillator 51 using the vibration element 30 as the source oscillation both originate from the vibration energy of the vibration element 30. Therefore, even if a disturbance such as an impact or noise is applied to the optical modulator 12 and changes the vibration of the vibration element 30, both the modulation signal and the reference signal change in the same way. This allows the effects of both disturbances to be offset or reduced during the arithmetic processing in the demodulation circuit 52. As a result, a decrease in the S / N ratio (signal-to-noise ratio) of the sample signal demodulated by the demodulation circuit 52 can be suppressed.

[0035] The vibration element 30 is a vibrator that generates a periodic signal, such as a quartz crystal vibrator, a ceramic vibrator, or a Si vibrator. These vibrators utilize the mechanical resonance phenomenon, and therefore have a high Q value and excellent frequency stability.

[0036] Examples of quartz crystal resonators include quartz crystal AT resonators, SC cut quartz crystal resonators, tuning fork type quartz crystal resonators, quartz crystal surface acoustic wave elements, etc. The oscillation frequency of a quartz crystal resonator is, for example, about 1 kHz to several hundred MHz.

[0037] A silicon vibrator is a vibrator that includes a single-crystal silicon piece manufactured from a single-crystal silicon substrate using MEMS technology, and a piezoelectric film. MEMS (Micro Electro Mechanical Systems) stands for microelectromechanical systems. Examples of the shape of the single-crystal silicon piece include cantilever beam shapes such as two-legged tuning fork and three-legged tuning fork, and doubly supported beam shapes. The oscillation frequency of a silicon vibrator is, for example, about 1 kHz to several hundred MHz.

[0038] A ceramic vibrator is a vibrator that includes electrodes and piezoelectric ceramic pieces manufactured by baking and hardening piezoelectric ceramics. Examples of piezoelectric ceramics include lead zirconate titanate (PZT) and barium titanate (BTO). The oscillation frequency of a ceramic vibrator is, for example, from several hundred kHz to several tens of MHz.

[0039] Of these, a quartz crystal oscillator is preferably used for the oscillator element 30. The quartz crystal oscillator has particularly high frequency stability because the quartz crystal itself is a piezoelectric material.

[0040] The oscillation frequency of the vibration element 30 is not particularly limited, but is preferably between 1 MHz and 100 MHz. In the frequency band within this range, there are many vibrators with a high Q value of mechanical resonance. Therefore, by setting the oscillation frequency within this range, the reference signal I output from the signal oscillator 51 can be S1 The first frequency f M This can stabilize the system.

[0041] FIG. 3 is a perspective view showing an example of the configuration of the optical modulator 12 shown in FIG. An example of the optical modulator 12 shown in Fig. 3 is the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156. Specifically, the optical modulator 12 shown in Fig. 3 includes a vibration element 30 and a diffraction grating 434 that is provided in the vibration element 30 and diffracts the first divided light L1a (divided laser light).

[0042] The vibrating element 30 shown in Fig. 3 is a quartz crystal AT vibrator that vibrates in a thickness-shear mode along a vibration direction 436 in a high frequency region of the MHz band. The vibrating element 30 is also provided with a diffraction grating 434. The diffraction grating 434 has a plurality of linear grooves 432 that extend in a direction intersecting with the vibration direction 436. When such a diffraction grating 434 is irradiated with the first divided light L1a, the frequency of the first divided light L1a can be modulated to generate the reference light L2, even when the vibrating element 30 vibrates in a thickness-shear mode.

[0043] The vibration element 30 has a front surface 4311 and a back surface 4312, which are opposite surfaces. A diffraction grating 434 is disposed on the front surface 4311. A first electrode 437 for applying a voltage to the vibration element 30 and a pad 433 electrically connected to the first electrode 437 are disposed on the front surface 4311. A second electrode 438 for applying a voltage to the vibration element 30 and a pad 435 electrically connected to the second electrode 438 are disposed on the back surface 4312. The first electrode 437 and the second electrode 438 are disposed so as to overlap each other with the vibration element 30 interposed therebetween when the front surface 4311 is viewed from above. The pads 433 and 435 are disposed so as not to overlap each other with the vibration element 30 interposed therebetween. When a voltage is applied between the first electrode 437 and the second electrode 438, thickness-shear vibration is induced in the portion where the first electrode 437 and the second electrode 438 overlap.

[0044] Diffraction grating 434 shown in Fig. 3 is disposed on first electrode 437. That is, in Fig. 3, diffraction grating 434 is configured by a plurality of grooves 432 formed on the surface of first electrode 437, and when first divided light L1a is irradiated onto this, reference light L2 is emitted as diffracted light.

[0045] Diffraction grating 434 shown in Fig. 3 is a blazed diffraction grating, for example. A blazed diffraction grating is a diffraction grating whose cross-sectional shape is stepped. However, the shape of diffraction grating 434 is not limited to this.

[0046] Fig. 4 is a perspective view showing another example of the configuration of the optical modulator 12 shown in Fig. 2. In Fig. 4, three mutually orthogonal axes are set as A-axis, B-axis, and C-axis, and are indicated by arrows. The tip end of the arrow is designated as "plus" and the base end of the arrow is designated as "minus."

[0047] The vibrating element 30 shown in FIG. 4 is a tuning fork type quartz crystal vibrator. The vibrating element 30 shown in FIG. 4 has a vibrating substrate having a base 401 and a first vibrating arm 402 and a second vibrating arm 403. Such tuning fork type quartz crystal vibrators are readily available due to established manufacturing techniques, and also have stable oscillation. For this reason, tuning fork type quartz crystal vibrators are suitable as the vibrating element 30. The optical modulator 12 shown in FIG. 4 includes the vibrating element 30, and electrodes 404, 405 and a light reflecting portion 406 provided on the vibrating element 30.

[0048] The base 401 is a portion extending along the A-axis. The first vibrating arm 402 is a portion extending from the end of the base 401 on the negative side of the A-axis toward the positive side of the B-axis. The second vibrating arm 403 is a portion extending from the end of the base 401 on the positive side of the A-axis toward the positive side of the B-axis.

[0049] Electrode 404 is a conductive film provided on the side surfaces parallel to plane AB of first vibrating arm 402 and second vibrating arm 403. Although not shown in Fig. 4, electrodes 404 are provided on the opposing side surfaces, and drive first vibrating arm 402 and second vibrating arm 403 by applying voltages of different polarities to the electrodes.

[0050] Electrode 405 is a conductive film provided on the side surfaces that intersect with plane AB of first vibrating arm 402 and second vibrating arm 403. Although not shown in Fig. 4, electrodes 405 are also provided on the opposing side surfaces, and drive first vibrating arm 402 and second vibrating arm 403 by applying voltages of mutually opposite polarities.

[0051] The light reflecting portion 406 is set on, for example, the side surface of the first vibrating arm 402 and the second vibrating arm 403 that intersects with the AB plane, and has the function of reflecting the first divided light L1a. Due to this function, the light reflecting portion 406 has a vibration component with a large amplitude in the incident direction of the incident first divided light L1a, and therefore can efficiently modulate the frequency of the first divided light L1a and generate the reference light L2.

[0052] Tuning-fork quartz crystal resonators use quartz crystal blanks cut from quartz crystal substrates. Examples of quartz crystal substrates used in manufacturing tuning-fork quartz crystal resonators include quartz crystal Z-cut flat plates. In FIG. 4, the X-axis is parallel to the A-axis, the Y'-axis is parallel to the B-axis, and the Z'-axis is parallel to the C-axis. A quartz crystal Z-cut flat plate is a substrate cut from a quartz crystal single crystal so that the X-axis is the electrical axis, the Y'-axis is the mechanical axis, and the Z'-axis is the optical axis. Specifically, in a Cartesian coordinate system consisting of the X-axis, Y'-axis, and Z'-axis, a substrate with a main surface tilted counterclockwise about the X-axis by approximately 1° to 5° from the X-Y' plane consisting of the X-axis and Y'-axis is preferably used as a quartz crystal substrate. Then, by etching such a quartz crystal substrate, a quartz crystal blank used in the vibration element 30 shown in FIG. 4 is obtained.

[0053] 1.3.Signal Oscillator The signal oscillator 51 shown in FIG. 1 generates a first frequency f M The reference signal I S1 Generates.

[0054] Examples of the signal oscillator 51 include an oscillator circuit using an inverter, a Colpitts oscillator circuit, and the like. These oscillator circuits operate using the fundamental wave oscillation of the oscillator element 30 as a source oscillation. For this reason, by using an oscillator element 30 with a high Q value of mechanical resonance, a reference signal I with high frequency stability can be generated. S1 can be generated.

[0055] The optical modulator 12 and the signal oscillator 51 may be housed in a single package, which reduces the physical distance between them and reduces the influence of noise and the like.

[0056] 1.4. Demodulation circuit First, the configuration of the demodulation circuit 52 will be described.

[0057] 1.4.1. Demodulation Circuit Configuration The demodulation circuit 52 shown in FIG. 1 includes a current-voltage converter 520, a high-pass filter 522 (DC offset removal unit), a band-pass filter 524 (third filter), a first phase adjuster 526, a first multiplier 530, a second multiplier 532, a low-pass filter 534 (first filter), a low-pass filter 536 (second filter), an A / D converter 538, an A / D converter 540, a first amplitude adjuster 542 and a second amplitude adjuster 544 (amplitude adjustment units), a divider 546, an arctangent calculator 548 (phase calculator), and a signal output unit 550.

[0058] The current-voltage converter 520 is also called a transimpedance amplifier (TIA), and converts the photocurrent output from the light receiving element 10 into a voltage signal, which is output as a laser light receiving signal.

[0059] The high-pass filter 522 removes the offset of the direct current component (DC offset) of the laser beam reception signal, thereby obtaining a laser beam reception signal composed of alternating current components.

[0060] The band-pass filter 524 filters the reference signal output from the signal oscillator 51 at a first frequency f M This allows only the components of the frequency component (noise component) to pass through. As a result, a reference signal from which unnecessary frequency components (noise components) have been removed is obtained. Note that if the reference signal output from signal oscillator 51 contains few unnecessary frequency components, band-pass filter 524 may be omitted.

[0061] First phase adjuster 526 adjusts the phase of the reference signal output from bandpass filter 524. Specifically, first phase adjuster 526 adjusts the phase of the reference signal so that it becomes in phase with the phase of the fundamental frequency component of the modulated signal included in the laser beam reception signal. The reference signal output from first phase adjuster 526 is split into two at branch point 527.

[0062] The first multiplier 530 multiplies the laser beam reception signal output from the high-pass filter 522 by the reference signal output from the first phase adjuster 526. This results in a first multiplied signal. The first multiplied signal is split at a branch point 531 into a first calculation path PS1 and a second calculation path PS2.

[0063] The second multiplier 532 multiplies the first multiplied signal divided into the second operation path PS2 by the reference signal output from the first phase adjuster 526. This results in a second multiplied signal.

[0064] The low-pass filter 534 cuts out high-frequency components from the first multiplied signal that has been split into the first calculation path PS1. This results in a first multiplied signal that includes low-frequency components. The low-pass filter 534 may also be a band-pass filter.

[0065] The low-pass filter 536 cuts out high-frequency components from the second multiplied signal output from the second multiplier 532. This results in a first multiplied signal containing low-frequency components. The low-pass filter 536 may be a band-pass filter.

[0066] The high-pass filter 522 (DC offset removal unit), band-pass filter 524, first phase adjuster 526, first multiplier 530, second multiplier 532, low-pass filter 534, and low-pass filter 536 are components of an analog circuit.

[0067] The A / D converter 538 converts the analog first multiplied signal output from the low-pass filter 534 into a digital signal, thereby obtaining a digital first multiplied signal.

[0068] The A / D converter 540 converts the analog second multiplied signal output from the low-pass filter 536 into a digital signal, thereby obtaining a digital second multiplied signal.

[0069] The first amplitude adjuster 542 and the second amplitude adjuster 544 adjust the amplitude of the first multiplied signal and the amplitude of the second multiplied signal so that the amplitudes of the input signals are aligned with each other. This improves the demodulation accuracy of phase X. Note that these may be provided as needed, and may be omitted, for example, when the deviation in the amplitude of the input signals is small. Furthermore, when adjustment is possible using only one of the first amplitude adjuster 542 or the second amplitude adjuster 544, the other may be omitted.

[0070] Divider 546 performs division by dividing the first multiplied signal output from first amplitude adjuster 542 by the second multiplied signal output from second amplitude adjuster 544. In this way, a divided signal is obtained.

[0071] The arctangent calculator 548 performs an arctangent calculation on the divided signal output from the divider 546. In this way, the phase is calculated as sample information derived from the object 14.

[0072] The signal output unit 550 performs phase unwrapping, such as unwrapping, on the phase derived from the object 14. Furthermore, it calculates the displacement and velocity of the object 14 as necessary.

[0073] Although first amplitude adjuster 542, second amplitude adjuster 544, divider 546, arctangent calculator 548, and signal output unit 550 may constitute an analog circuit, they are preferably components of a digital circuit. Such a digital circuit is implemented in an electronic device such as an FPGA (programmable logic device), an ASIC (application-specific integrated circuit), or a microcomputer.

[0074] 1.4.2. Demodulation process Next, we will explain the operation (demodulation process) of the demodulation circuit 52. In the following explanation, as an example, a signal whose frequency changes sinusoidally is used as the modulation signal, and the displacement of the object 14 is a simple harmonic motion in the optical axis direction.

[0075] The laser beam reception signal output from the current-voltage converter 520 is input to a high-pass filter 522. The high-pass filter 522 removes the DC offset from the laser beam reception signal. This results in a laser beam reception signal consisting of an AC component. The AC component is then filtered as I PD.AC In the following explanation, the AC component I PD.AC , the laser light reception signal I output from the high-pass filter 522. PD.AC The laser light reception signal I output from the high-pass filter 522 PD.AC is expressed by the following formula (1).

[0076]

number

[0077] In the above formula (1), A is the amplitude. M is the phase originating from the optical modulator 12. Furthermore, X is the phase given by the following equation (1a).

[0078]

number

[0079] In the above formula (1a), Φ S is the phase originating from the object 14, and Φ 0 is the initial phase difference due to the optical path difference in the interference optical system 50.

[0080] The optical modulator 12 shown in FIG. M Therefore, a reference light L2 containing a modulation signal of Φ M is given by the following equation (1b).

[0081]

number

[0082] In the above equation (1b), B is the modulation phase shift in the frequency modulation by the optical modulator 12. Also, t is time. Using the above formula (1b), the above formula (1) can be expressed as the following formula (1c).

[0083]

number

[0084] The right-hand side of the above formula (1c) is a mathematical expression containing a trigonometric function whose angle part is a time-varying trigonometric function. In this case, by using the series representation of the Bessel function, the right-hand side of the above formula (1c) can be expanded as shown in the following formula (1d).

[0085]

number

[0086] The above equation (1d) is the modulation angular frequency ω M (DC term) and sinω M The term containing t (sinω M t term) and cos2ω M The term containing t (cos2ω M and terms that represent harmonic components such as the t term. Figure 5 shows a table summarizing these terms and the coefficients included in each term.

[0087] FIG. 5 is a table showing coefficients included in the DC term and the term representing the harmonic component in the series representation of the laser beam reception signal.

[0088] 5, the coefficients of each term include cosX or sinX. The demodulation circuit 52 extracts these by calculation, and finally obtains the phase Φ S In particular, in this embodiment, sinω M The coefficient of the t term contains sinX and cos2ω M The cosX and cosX contained in the coefficient of the t term are extracted, and the phase X is finally found.

[0089] Here, the reference signal I output from the first phase adjuster 526 S1 is expressed by the following formula (2).

[0090]

number

[0091] In the above formula (2), V q is the amplitude. Also, ω M is the modulation frequency f M is the angular frequency (modulation angular frequency), and 2πf M is.

[0092] The first multiplier 530 multiplies the laser beam reception signal I output from the high-pass filter 522 by PD.AC and the reference signal I output from the first phase adjuster 526. S1 and are multiplied by each other. This multiplication (first multiplication) is an operation of multiplying the above equation (1d) by the above equation (2). As a result, a first product signal is obtained. The first product signal is split at the branch point 531 shown in FIG. 1. The high frequency components of the first product signal split into the first calculation path PS1 are cut by the low pass filter 534. The cutoff angular frequency of the low pass filter 534 is, for example, ω M As a result, the first multiplied signal output from the low-pass filter 534 is a signal composed of the DC component shown in Fig. 5. This component includes sinX, while the modulation angular frequency ω M Therefore, the above processing reduces the frequency of the first multiplied signal.

[0093] The concept of this first multiplication is shown in Figure 5. In Figure 5, arrows are used to conceptually show how sinX and cosX included in the coefficients change through the first multiplication and the second multiplication described later. When the first multiplication is performed, sinω M The sinX included in the coefficient of the t term is the coefficient of the DC term and cos2ω M We move on to the coefficients of the t term. Also, cos2ω MThe cosX included in the coefficient of the t term is sinω M Coefficient of t term and sin3ω M The coefficients of the t term are shifted to sinX or cosX, respectively. Similarly, the other terms shift from the base of the arrow to the tip.

[0094] Next, when the harmonic components are removed in the low-pass filter 534, only the DC term is output. In other words, among the results of the first multiplication shown in FIG. 5, the DC term components including the coefficients enclosed in the thick solid frame are output from the low-pass filter 534. The first multiplied signal I het1 is expressed by the following formula (3).

[0095]

number

[0096] In the second multiplier 532, the first multiplied signal I het1 and the reference signal I output from the first phase adjuster 526. S1 This multiplication (second multiplication) is an operation of multiplying the first multiplied signal by the above formula (2). As a result, the second multiplied signal is obtained. The high frequency components of the second multiplied signal are cut by the low-pass filter 536. The cutoff angular frequency of the low-pass filter 536 is, for example, ω M As a result, the second multiplied signal output from the low-pass filter 536 is a signal composed of the DC component shown in FIG. 5. This component includes cosX, while the modulation angular frequency ω M Therefore, the above processing reduces the frequency of the second multiplied signal.

[0097] The concept of this second multiplication is shown in Figure 5. When the second multiplication is performed, the sinω M The cosX included in the coefficient of the t term (coefficient surrounded by a thick dashed frame) is the coefficient of the DC term and cos2ω MThe coefficients of the t term are shifted to sinX or cosX, respectively. Similarly, the other terms shift from the base of the arrow to the tip.

[0098] Next, when the harmonic components are removed in the low-pass filter 536, only the DC term is output. In other words, among the results of the second multiplication shown in FIG. 5, the DC term components including the coefficients enclosed in the thick solid frame are output from the low-pass filter 536. The second multiplication signal I het2 is expressed by the following formula (4).

[0099]

number

[0100] In this way, the first product signal and the second product signal can be made lower in frequency, and the first product signal I het1 , and the second multiplication signal I, which is composed of components including cosX het2 can be output to A / D converter 538 and A / D converter 540.

[0101] In the results of the first multiplication shown in Figure 5, for coefficients enclosed in a thick dashed frame, the transition of cosX represented by the dashed arrow and the transition of cosX represented by the thick solid arrow overlap. In this case, cosX after the transition represented by the dashed arrow can become a noise component for cosX after the transition represented by the solid arrow, and therefore needs to be removed.

[0102] Therefore, in this embodiment, the demodulation circuit 52 is provided with the high-pass filter 522 described above. As described above, this high-pass filter 522 removes the DC offset from the laser beam reception signal. By removing the DC offset, the coefficients (coefficients of the DC term) underlined in FIG. 5 are removed. This makes it possible to stop the transition of cosX indicated by the dashed arrow. As a result, it is possible to prevent the superposition of noise components.

[0103] The first multiplied signal I is digitally converted by the A / D converter 538. het1 is input to the first amplitude adjuster 542. The second multiplied signal I het2 is input to the second amplitude adjuster 544. The first amplitude adjuster 542 and the second amplitude adjuster 544 adjust the amplitudes of the input signals so that they are aligned with each other. Specifically, the first amplitude adjuster 542 adjusts J2(b)V q The first amplitude adjuster 542 multiplies the first multiplied signal I het1 , and the second multiplied signal I output from the second amplitude adjuster 544 het2 are given by the following equations (5) and (6), respectively.

[0104]

number

[0105]

number

[0106] The divider 546 divides the first multiplied signal I output from the first amplitude adjuster 542. het1 is the second multiplied signal I output from the second amplitude adjuster 544. het2 A division is performed by dividing by , whereby a divided signal is obtained.

[0107] The arctangent calculator 548 performs an arctangent calculation on the division signal output from the divider 546. The arctangent calculation result I atan is expressed by the following formula (7).

[0108]

number

[0109] The arctangent calculation result I expressed by the above formula (7) atan The phase X can be calculated from In the demodulation process described above, the first multiplied signal I het1 and the second multiplied signal I het2 Each frequency is modulated at a frequency f M In other words, the frequency is down-converted. This allows the corresponding frequency of the A / D converters 538 and 540 to be lowered, and the cost of the A / D converters 538 and 540 can be reduced.

[0110] Furthermore, the digital circuits described above are implemented in, for example, FPGAs, and the down-conversion described above can also lower the supported frequency of the FPGAs, etc. Therefore, the down-conversion described above can also contribute to reducing the cost of electronic components such as FPGAs.

[0111] Furthermore, the modulation frequency f M For example, it is possible to remove the constraints on the modulation frequency f M It also becomes easy to use a vibrating element with a very high oscillation frequency, for example, a vibrating element with an oscillation frequency in the MHz range, in the optical modulator 12. This makes it possible to widen the selection of vibrating elements that can be used.

[0112] Furthermore, the analog circuit described above has only two multipliers, which is a small number. This reduces the amount of noise introduced by the multiplication, enabling highly accurate calculation of the phase X.

[0113] 2. Second embodiment Next, a laser interferometer according to a second embodiment will be described.

[0114] The second embodiment will be described below, but the following description will focus on the differences from the previous embodiment, and a description of similar points will be omitted.

[0115] The second embodiment is similar to the first embodiment except that the configuration of the high-pass filter 522 is different.

[0116] The high-pass filter 522 removes the DC offset of the laser light reception signal and passes the AC component. However, depending on the frequency characteristics of the phase delay amount of the AC component passing through the high-pass filter 522, M t term and cos2ω M The difference in the amount of phase delay between the t term and the X term becomes large, which may result in a decrease in the demodulation precision and accuracy of the phase X.

[0117] FIG. 6 is a graph showing an example of the frequency characteristics of the phase delay amount of the AC component passing through the high-pass filter 522 shown in FIG. 1. The horizontal axis is frequency. The left vertical axis is gain. The right vertical axis is the phase delay amount when the gain is zero. The passband shown in FIG. 6 is a band designed according to the frequency of the AC component to be passed through the high-pass filter 522. In the example shown in FIG. 6, the modulation frequency f M Assuming that the frequency is 5 MHz, the passband is set with a lower limit of 5 MHz and an upper limit of 10 MHz, which is twice the frequency. By minimizing the difference in the phase delay within this passband, it is possible to prevent a decrease in the demodulation accuracy and precision of phase X.

[0118] Here, the reason why the difference in the amount of phase delay within the passband affects the demodulation accuracy of the phase X will be considered.

[0119] In FIG. 6, the phase delay amount when a 5 MHz component passes is Φ1, and the phase delay amount when a 10 MHz component, which is twice the 5 MHz component, passes is Φ2. Then, the difference in the phase delay amount ψ1 within the passband is given by |Φ1-Φ2|. This difference in the phase delay amount ψ1 is calculated by the arctangent calculation result I in the demodulation process. atan The influence expressed by the following formula (8) is exerted on

[0120]

number

[0121] The right side of the above equation (8) includes cos ψ1 and is different from the right side of the above equation (7). This difference is an error factor that reduces the demodulation accuracy of the phase X.

[0122] Therefore, in this embodiment, the high-pass filter 522 is set so that the difference ψ1 in the phase delay amount satisfies the following equation (9).

[0123]

number

[0124] Preferably, the high-pass filter 522 is set so as to satisfy the following formula (10).

[0125]

number

[0126] Such a configuration can improve the accuracy and precision of demodulation of the phase X. As a result, the accuracy of measuring the displacement of the object 14 and the accuracy of the measured displacement can be improved.

[0127] FIG. 7 is a graph showing the results of simulating the influence of the difference ψ1 in the amount of phase delay on the measurement accuracy of displacement in the design example shown in FIG.

[0128] 7, when the difference in the phase delay amount ψ1 is 10 degrees or less, the displacement measurement accuracy is suppressed to 1 nm or less. Therefore, by setting the difference in the phase delay amount ψ1 within the above range, sufficient measurement accuracy can be obtained.

[0129] FIG. 8 is a graph showing the results of simulating the effect of the difference ψ1 in the amount of phase delay on the accuracy of displacement in the design example shown in FIG.

[0130] 8, when the difference in the phase delay amount ψ1 is 1 [deg] or less, the accuracy of the measured displacement is kept within 100±0.01%. Therefore, by setting the difference in the phase delay amount ψ1 within the above range, sufficient measurement accuracy can be obtained.

[0131] As described above, methods for keeping the difference ψ1 in the amount of phase delay within a predetermined range include, for example, changing the constants of the elements in the LCR circuit, increasing the number of stages, lowering the cutoff frequency, etc. in the design of high-pass filter 522.

[0132] Figure 9 is a graph created by calculating the frequency characteristics of gain (bandwidth characteristics) and frequency characteristics of phase delay (phase characteristics) when the number of stages in a high-pass filter composed of an LCR circuit is changed from 1 to 3. Changing the number of stages shifts the cutoff frequency of the bandwidth characteristics, and also the phase characteristics.

[0133] In the design example shown in Figure 9, when the number of stages in the LCR circuit is three, the difference in phase delay ψ1 is kept to 10 degrees or less. By adjusting the design of the LCR circuit in this way, it is possible to keep the difference in phase delay ψ1 to 10 degrees or less, or to 1 degree or less. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0134] 3. Modification of the Second Embodiment Next, a laser interferometer 1 according to a modification of the second embodiment will be described.

[0135] A modified example of the second embodiment will be described below, but the following description will focus on the differences from the second embodiment, and a description of similar points will be omitted.

[0136] In the modification of the second embodiment, an operation of dividing the signal input to the second amplitude adjuster 544 by cos ψ1 is added. This operation of dividing by cos ψ1 corresponds to an adjustment that cancels out the amplitude change amount that reflects the difference ψ1 in the phase delay amount. This makes it possible to cancel out or reduce the error factor expressed by the above equation (8). As a result, the accuracy and precision of the demodulation of the phase X can be improved compared to the second embodiment.

[0137] Furthermore, by adding the above calculation, the load of designing the high-pass filter 522 can be reduced. In the above-described modified example, the same effects as those of the second embodiment can be obtained.

[0138] 4. Third embodiment Next, a laser interferometer 1 according to a third embodiment will be described. FIG. 10 is a functional block diagram showing a laser interferometer 1 according to the third embodiment.

[0139] The third embodiment will be described below, but the following description will focus on the differences from the previous embodiment, and a description of similar points will be omitted.

[0140] The third embodiment is similar to the first embodiment except for the configuration of the demodulation circuit 52. Specifically, in the third embodiment, a second phase adjuster 528 is added to the demodulation circuit 52.

[0141] 10 is provided between branch point 527 and second multiplier 532. That is, second phase adjuster 528 further adjusts the phase of the reference signal whose phase has been adjusted by first phase adjuster 526.

[0142] As in the first embodiment, first phase adjuster 526 adjusts the phase of the reference signal so that it becomes in phase with the phase of the fundamental frequency component of the modulated signal included in the laser beam reception signal. In contrast, second phase adjuster 528 adjusts the phase of one of the reference signals output from first phase adjuster 526 and branched at branch point 527 so as to cancel out difference ψ1 in the phase delay amount in high-pass filter 522. As a result, even if difference ψ1 in the phase delay amount exists in high-pass filter 522, the influence of this difference can be canceled out or reduced in the second multiplication in second multiplier 532.

[0143] The above effects will be verified below using calculation formulas. When passing through the high-pass filter 522, the laser light reception signal I PD.AC The influence of the difference ψ1 in the amount of phase delay that occurs between the first and second signals is expressed by the following equation (1e).

[0144]

number

[0145] The first multiplier 530 multiplies the laser beam reception signal I output from the high-pass filter 522 by PD.AC and the reference signal I output from the first phase adjuster 526. S1 This results in a first multiplied signal I het1 is expressed by the following formula (11).

[0146]

number

[0147] After that, the harmonic components are removed by the low-pass filter 534, and only the DC term is output. The amplitude is also adjusted by the first amplitude adjuster 542. As a result, the first multiplied signal I het1 is expressed by the following formula (12).

[0148]

number

[0149] On the other hand, as a result of the phase adjustment by the second phase adjuster 528, the reference signal I S2 is expressed by the following formula (13).

[0150]

number

[0151] In the second multiplier 532, the first multiplied signal I het1 and the reference signal I output from the second phase adjuster 528. S2 This results in a second multiplied signal I het2 The second multiplication signal I het2 is expressed by the following formula (14).

[0152]

number

[0153] After that, the harmonic components are removed by the low-pass filter 536, and only the DC term is output. The amplitude is also adjusted by the second amplitude adjuster 544. As a result, the second multiplied signal I het2 is expressed by the following formula (15).

[0154]

number

[0155] As described above, the influence of the difference ψ1 in the amount of phase delay disappears in both equation (12) and equation (15). Therefore, by providing the second phase adjuster 528, the influence of the phase characteristics in the high-pass filter 522 can be suppressed. As a result, the demodulation precision and accuracy of the phase X can be further improved. In addition, the design load of the high-pass filter 522 can be reduced.

[0156] Here, the phase adjustment amount in second phase adjuster 528 is denoted as ψ2. Ideally, phase adjustment amount ψ2 should be equal to the difference ψ1 in the phase delay amounts in high-pass filter 522, but a setting error may occur. Therefore, the influence of setting error δ (=|ψ2 - ψ1|) will be examined.

[0157] The influence of the setting error δ is the same as the influence of the difference ψ1 in the amount of phase delay in the second embodiment.

[0158] Specifically, by keeping the setting error δ to 10 degrees or less, the displacement measurement accuracy can be kept to 1 nm or less, which provides sufficient measurement accuracy.

[0159] Furthermore, by keeping the setting error δ to 1 [deg] or less, the accuracy of the measured displacement can be kept within 100±0.01%, which provides sufficient measurement accuracy. In the third embodiment as described above, the same effects as in the first embodiment can be obtained.

[0160] 5. Fourth embodiment Next, a laser interferometer 1 according to a fourth embodiment will be described. FIG. 11 is a functional block diagram showing a laser interferometer 1 according to the fourth embodiment.

[0161] The fourth embodiment will be described below, but the following description will focus on the differences from the previous embodiment, and a description of similar points will be omitted. The fourth embodiment is similar to the third embodiment except that the configuration of the demodulation circuit 52 is different.

[0162] In the third embodiment described above, the first phase adjuster 526 is provided between the bandpass filter 524 and the branch point 527 , and the second phase adjuster 528 is provided between the branch point 527 and the second multiplier 532 .

[0163] In contrast to this, in the fourth embodiment, a first phase adjuster 526 is provided between a branch point 527 and a first multiplier 530. Accordingly, the phase adjustment amount ψ2 in a second phase adjuster 528 is changed.

[0164] Therefore, the fourth embodiment is similar to the third embodiment except that the arrangement and setting of first phase adjuster 526 are different.

[0165] As in the first embodiment, the first phase adjuster 526 adjusts the phase of the reference signal so that it becomes in phase with the phase of the fundamental frequency component of the modulated signal included in the laser light reception signal.

[0166] On the other hand, the second phase adjuster 528 adjusts the phase of one of the reference signals output from the band-pass filter 524 and branched at the branch point 527 so that it is in phase with the phase of the fundamental frequency component of the modulated signal included in the laser beam reception signal, and also adjusts it so as to cancel the difference ψ1 in the amount of phase delay in the high-pass filter 522. This provides the same effects as the third embodiment.

[0167] The above effects will be verified below. When the first phase adjuster 526 adjusts the phase of the reference signal so that it becomes in phase with the phase of the fundamental frequency component of the modulated signal included in the laser light reception signal, the amount of phase adjustment is set to ψ0.

[0168] Second phase adjuster 528 adjusts the phase of one of the reference signals branched at branch point 527 so that the phase becomes in phase with the phase of the fundamental frequency component of the modulated signal included in the laser beam reception signal. Therefore, the phase adjustment amount ψ2 in second phase adjuster 528 is set so that ψ2=ψ0.

[0169] Furthermore, in this embodiment, the phase adjustment amount ψ2 in the second phase adjuster 528 also includes an adjustment amount that offsets the difference ψ1 in the phase delay amount in the high-pass filter 522. Therefore, the phase adjustment amount ψ2 in the second phase adjuster 528 is set to be ψ2=ψ0+ψ1.

[0170] In the fourth embodiment, too, the setting error δ (=|ψ2-ψ1|) of the phase adjustment amount ψ2 can be kept to 10 degrees or less, thereby making it possible to keep the displacement measurement accuracy to 1 nm or less. This allows for sufficient measurement accuracy to be achieved.

[0171] Furthermore, by keeping the setting error δ to 1 [deg] or less, the accuracy of the measured displacement can be kept within 100±0.01%, which provides sufficient measurement accuracy. In the fourth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0172] 6. Fifth embodiment Next, a spectroscopic device according to a fifth embodiment will be described. FIG. 12 is a functional block diagram showing a spectroscopic device 900 according to the fifth embodiment.

[0173] The fifth embodiment will be described below, focusing on the differences from the first embodiment, and a description of the same points will be omitted. Note that in Fig. 12, the same components as those in Fig. 1 are denoted by the same reference numerals.

[0174] The spectroscopic device 900 shown in FIG. 12 includes the laser interferometer 1 according to each of the above-described embodiments and a spectroscopic analysis unit 910.

[0175] The spectroscopic analysis unit 910 receives analytical light including a sample-derived signal generated by interaction with the sample, and generates spectral information derived from the sample. The spectroscopic analysis unit 910 shown in FIG. 12 includes a spectroscopic optical system 920 and a calculation unit 930. The spectroscopic optical system 920 includes an analytical light source 922, a movable mirror 924, and an analytical light receiving unit 926. In the spectroscopic optical system 920, the analytical light emitted from the analytical light source 922 is irradiated onto the sample, and then the analytical light is incident on an analytical light interferometer. In the analytical light interferometer, the movable mirror 924 is moved to change the optical path length, causing interference between the analytical light that has passed through the sample and the analytical light that has passed through the movable mirror 924. The interference light is then received by the analytical light receiving unit 926, and an analytical light receiving signal is obtained.

[0176] On the other hand, laser interferometer 1 measures the displacement of movable mirror 924 and outputs a mirror position signal. Laser interferometer 1 can accurately measure the displacement of movable mirror 924, and therefore can generate a highly accurate mirror position signal.

[0177] The calculation unit 930 generates a waveform (interferogram) representing the intensity of the interference light relative to the optical path length within the spectroscopic optical system 920 based on the analytical light receiving signal and the mirror position signal, and performs a Fourier transform on this to generate spectroscopic spectrum information.

[0178] Therefore, the spectroscopic analysis section 910 can generate highly accurate spectroscopic spectrum information based on the measurement results of the displacement of the movable mirror 924 by the laser interferometer 1.

[0179] Furthermore, as mentioned above, the cost of the laser interferometer 1 can be easily reduced. Therefore, with the above-described configuration, it is possible to realize a spectrometer 900 that is easy to reduce in cost and has excellent wavenumber resolution.

[0180] The spectroscopic device 900 can be applied to FT-IR (Fourier infrared spectroscopy), FT-NIR (Fourier near-infrared spectroscopy), FT-VIS (Fourier visible spectroscopy), FT-UV (Fourier ultraviolet spectroscopy), FT-THz (Fourier terahertz spectroscopy), etc. by appropriately changing the type of analytical light, etc.

[0181] Furthermore, by using an element capable of acquiring a two-dimensional light intensity distribution as the analytical light receiving section 926, the spectroscopic device 900 can be applied to, for example, a white light interferometry measuring device, an optical coherence tomography (OCT) imaging device, and the like.

[0182] 7. Effects of the above embodiments The laser interferometer 1 according to each of the above embodiments is a laser interferometer that irradiates the object 14 with the second divided light L1b (laser light) and receives the object light L3 (laser light) that has passed through the object 14 to acquire the displacement of the object 14. It includes a laser light source 2, an optical modulator 12, a light-receiving element 10, a signal oscillator 51, and a demodulation circuit 52. The laser light source 2 emits the emitted light L1 (laser light). The optical modulator 12 includes a vibration element 30 and adds a modulation signal to the first divided light L1a (laser light) using the vibration element 30. The light-receiving element 10 detects intensity changes in the reference light L2 and the object light L3 (laser light) that include the sample signal added by the object 14 and the aforementioned modulation signal, and outputs a laser light reception signal. The signal oscillator 51 generates a reference signal of a first frequency using the vibration element 30 as a source oscillation. The demodulation circuit 52 demodulates the sample signal from the laser light reception signal based on the reference signal to obtain the displacement of the object 14 .

[0183] The demodulation circuit 52 includes a high-pass filter 522 (DC offset removal unit), a first phase adjuster 526, a first multiplier 530, a low-pass filter 534 (first filter), a second multiplier 532, a low-pass filter 536 (second filter), and an arctangent calculator 548 (phase calculator).

[0184] The high-pass filter 522 removes the offset of the DC component of the laser beam reception signal. The first phase adjuster 526 adjusts the phase of the reference signal. The first multiplier 530 multiplies the laser beam reception signal output from the high-pass filter 522 by the reference signal output from the first phase adjuster 526 and outputs a first product signal. The low-pass filter 534 removes high-frequency components contained in the first product signal. The second multiplier 532 multiplies the first product signal by the reference signal output from the first phase adjuster 526 and outputs a second product signal. The low-pass filter 536 removes high-frequency components contained in the second product signal. The arctangent calculator 548 calculates the phase originating from the target 14 as a sample signal based on the signal output from the low-pass filter 534 and the signal output from the low-pass filter 536.

[0185] With this configuration, two multiplications are performed in the demodulation circuit 52, thereby lowering the frequencies of the first and second product signals. In other words, the frequency of the signal used for arithmetic processing can be lowered. This allows the corresponding frequency of the A / D converters 538 and 540 and the FPGA in which part of the demodulation circuit 52 is implemented to be lowered, thereby reducing costs.

[0186] In the laser interferometer 1 according to each of the above embodiments, the demodulation circuit 52 has a band-pass filter 524 (third filter). The band-pass filter 524 is provided between the signal oscillator 51 and the first phase adjuster 526, and extracts the first frequency component contained in the reference signal.

[0187] With this configuration, a reference signal from which unnecessary frequency components (noise components) have been removed can be obtained.

[0188] In the laser interferometer 1 according to each of the above embodiments, the demodulation circuit 52 has a first amplitude adjuster 542 and a second amplitude adjuster 544 (amplitude adjustment unit). The first amplitude adjuster 542 and the second amplitude adjuster 544 adjust the amplitude of the first multiplied signal output from the low-pass filter 534 (first filter) and the amplitude of the second multiplied signal output from the low-pass filter 536 (second filter) to match each other.

[0189] According to this configuration, the first and second product signals having the same amplitude can be obtained, thereby improving the accuracy of demodulation of the phase X.

[0190] In the laser interferometer 1 according to each of the above embodiments, the high-pass filter 522 (DC offset removal unit) is set to satisfy ψ1≦10[deg], where ψ1 is the difference between the phase delay amount Φ1 when a frequency component of the modulated signal passes and the phase delay amount Φ2 when a frequency component twice that of the modulated signal passes.

[0191] Such a configuration can improve the accuracy and precision of demodulation of the phase X. This can improve the accuracy of measuring the displacement of the object 14 and the accuracy of the measured displacement.

[0192] In the laser interferometer 1 according to each of the above embodiments, the high-pass filter 522 (DC offset removal section) is set so that the difference ψ1 in the phase delay amount satisfies ψ1≦1 [deg].

[0193] Such a configuration can improve the accuracy and precision of demodulation of the phase X. This can improve the accuracy of measuring the displacement of the object 14 and the accuracy of the measured displacement.

[0194] In the laser interferometer 1 according to each of the above embodiments, the demodulation circuit 52 has a first amplitude adjuster 542 and a second amplitude adjuster 544 (amplitude adjustment unit). The first amplitude adjuster 542 and the second amplitude adjuster 544 adjust at least one of the amplitude of the first product signal output from the low-pass filter 534 (first filter) and the amplitude of the second product signal output from the low-pass filter 536 (second filter). The first amplitude adjuster 542 and the second amplitude adjuster 544 also have the function of adjusting the amplitude of the first product signal and the amplitude of the second product signal so as to match each other, and the function of adjusting the amplitude of the second product signal so as to cancel out the amount of amplitude change reflecting the difference ψ1 in the amount of phase delay.

[0195] According to this configuration, it is possible to cancel or reduce the error factors that reduce the accuracy of demodulation of phase X. As a result, it is possible to further improve the accuracy and precision of demodulation of phase X.

[0196] In the laser interferometer 1 according to each of the above embodiments, the first phase adjuster 526 adjusts the phase of the reference signal so that it is in phase with the fundamental frequency component of the modulated signal included in the laser beam reception signal.

[0197] With this configuration, the phase of the fundamental frequency component of the modulated signal included in the laser beam reception signal can be aligned with the phase of the reference signal, thereby preventing a decrease in the accuracy and precision of the demodulation of the phase X.

[0198] In the laser interferometer 1 according to each of the above embodiments, the demodulation circuit 52 has a second phase adjuster 528. The second phase adjuster 528 is provided between the signal oscillator 51 and the second multiplier 532, and adjusts the phase of the reference signal to be in phase with the fundamental frequency component of the modulated signal included in the laser light reception signal, and also adjusts the phase of the reference signal from the in-phase phase so that a phase adjustment amount ψ2 equal to the difference ψ1 in the phase delay amount in the pass band of the first frequency component of the high-pass filter 522 (DC offset removal unit) is generated.

[0199] According to this configuration, the influence of the difference ψ1 in the amount of phase delay in high-pass filter 522 can be canceled out or reduced in the multiplication by second multiplier 532. Furthermore, the load of designing high-pass filter 522 can be reduced.

[0200] In the laser interferometer 1 according to each of the above embodiments, the demodulation circuit 52 is provided between the first phase adjuster 526 and the second multiplier 532, and adjusts the phase of the reference signal output from the first phase adjuster 526 so that a phase adjustment amount ψ2 equal to the difference ψ1 in the phase delay amount in the passband of the high-pass filter 522 (DC offset removal section) for the first frequency component is generated.

[0201] According to this configuration, the influence of the difference ψ1 in the amount of phase delay in high-pass filter 522 can be canceled out or reduced in the multiplication by second multiplier 532. Furthermore, the load of designing high-pass filter 522 can be reduced.

[0202] Moreover, the spectroscopic device 900 according to the embodiment includes the laser interferometer 1 according to each embodiment and a spectroscopic analysis unit 910. The spectroscopic analysis unit 910 has a spectroscopic optical system 920 including a movable mirror 924, and generates spectroscopic spectral information derived from a sample. The laser interferometer 1 measures the displacement of the movable mirror 924. The spectroscopic analysis unit 910 generates spectroscopic spectral information based on the measurement result of the displacement of the movable mirror 924 by the laser interferometer 1. With this configuration, the cost of the spectroscopic device 900 can be easily reduced.

[0203] The laser interferometer and spectroscopic device of the present invention have been described above based on the illustrated embodiments, but the laser interferometer and spectroscopic device of the present invention are not limited to the above-described embodiments, and the configuration of each part may be replaced with any component, or any other component may be added.

[0204] Furthermore, in each of the above embodiments, a Michelson type interference optical system is used, but other types of interference optical systems may also be used. [Explanation of symbols]

[0205] 1...laser interferometer, 2...laser light source, 3...collimating lens, 4...light splitter, 6...half wave plate, 7...quarter wave plate, 8...quarter wave plate, 9...analyzer, 10...light receiving element, 12...optical modulator, 14...object, 18...optical path, 20...optical path, 22...optical path, 24...optical path, 30...vibration element, 50...interference optical system, 51...signal oscillator, 52...demodulation circuit, 401...base, 402...first vibrating arm, 403...second vibrating arm, 404...electrode, 405...electrode, 406...light reflecting portion, 432...groove, 433...pad, 434...diffraction grating, 435...pad, 436...vibration direction, 437...first electrode, 438...second electrode, 520...current-voltage converter, 522...high pass filter, 524...bandpass filter, 526...first phase adjuster, 527...branching point, 528...second phase adjuster, 530...first multiplier, 531...branching point, 532...second multiplier, 534...lowpass filter, 536...lowpass filter, 538...A / D converter, 540...A / D converter, 542...first amplitude adjuster, 544...second amplitude adjuster, 546...divider, 548...arctangent calculator, 550...signal output section, 900...spectrometer, 910...spectroscopic analysis section, 920...spectroscopic optical system, 922...analytical light source, 924...moving mirror, 926...analytical light receiving section, 930...calculation section, 4311...front surface, 4312...rear surface, f M ...modulation frequency, L1...emitted light, L1a...first divided light, L1b...second divided light, L2...reference light, L3...object light, PS1...first calculation path, PS2...second calculation path, Φ1...phase delay amount, Φ2...phase delay amount

Claims

1. A laser interferometer that irradiates a target with laser light, receives the laser light that has passed through the target, and acquires a displacement of the target, a laser light source that emits the laser light; an optical modulator including a vibration element, the optical modulator adding a modulation signal to the laser light by using the vibration element; a light receiving element that detects a change in intensity of the laser light including the sample signal and the modulation signal added by the object, and outputs a laser light receiving signal; a signal oscillator that generates a reference signal of a first frequency using the vibration element as a source of vibration; a demodulation circuit that demodulates the sample signal from the laser beam reception signal based on the reference signal to obtain the displacement of the object; Equipped with The demodulation circuit a DC offset removal unit that removes an offset of a DC component of the laser beam reception signal; a first phase adjuster for adjusting the phase of the reference signal; a first multiplier that multiplies the laser beam reception signal output from the DC offset removal unit by the reference signal output from the first phase adjuster, and outputs a first multiplied signal; a first filter that removes high frequency components contained in the first multiplied signal; a second multiplier that multiplies the first multiplied signal by the reference signal output from the first phase adjuster and outputs a second multiplied signal; a second filter that removes high frequency components contained in the second multiplied signal; a phase calculator that calculates a phase derived from the object as the sample signal based on the signal output from the first filter and the signal output from the second filter; A laser interferometer comprising:

2. The demodulation circuit a third filter provided between the signal oscillator and the first phase adjuster, the third filter extracting the first frequency component contained in the reference signal; 2. The laser interferometer of claim 1, wherein:

3. The demodulation circuit an amplitude adjustment unit that adjusts the amplitude of the first product signal output from the first filter and the amplitude of the second product signal output from the second filter to be equal to each other; 3. The laser interferometer according to claim 1, wherein:

4. The DC offset removal unit The difference between the amount of phase delay when a component of the frequency of the modulated signal passes and the amount of phase delay when a component of twice the frequency of the modulated signal passes is defined as ψ １ Then, ψ １ 3. The laser interferometer according to claim 1, wherein the interferometer is set to satisfy a condition of ≦10 degrees.

5. The DC offset removal unit calculates the difference ψ １ But, ψ １ 5. The laser interferometer according to claim 4, wherein the interferometer is set to satisfy the condition ≦1 [deg].

6. The demodulation circuit an amplitude adjustment unit that adjusts at least one of the amplitude of the first product signal output from the first filter and the amplitude of the second product signal output from the second filter; and The amplitude adjustment unit a function of adjusting the amplitude of the first multiplied signal and the amplitude of the second multiplied signal so that they are aligned with each other; The difference ψ between the phase delay amounts １ a function of adjusting the amplitude of the second multiplied signal so as to cancel out the amplitude change amount reflected in the second multiplied signal; 5. The laser interferometer of claim 4, wherein:

7. 2. The laser interferometer according to claim 1, wherein the first phase adjuster adjusts the phase of the reference signal so that the reference signal is in phase with a fundamental frequency component of the modulated signal contained in the laser beam reception signal.

8. The demodulation circuit a second phase adjuster provided between the signal oscillator and the second multiplier, which adjusts the phase of the reference signal to be in phase with the modulated signal included in the laser beam reception signal, and adjusts the phase of the reference signal from the in-phase phase so that a phase adjustment amount equal to a difference in phase delay amount of the first frequency component in the pass band of the DC offset removal unit is generated; 8. The laser interferometer of claim 7, wherein:

9. The demodulation circuit 9. The laser interferometer according to claim 7, wherein the laser interferometer is provided between the first phase adjuster and the second multiplier, and adjusts the phase of the reference signal output from the first phase adjuster so that a phase adjustment amount equal to a difference in phase delay amount in a pass band of the DC offset removal unit is generated from the phase of the reference signal output from the first phase adjuster.

10. a laser interferometer according to claim 1 or 2; a spectroscopic analysis unit having a spectroscopic optical system including a movable mirror and generating spectroscopic spectrum information derived from the sample; Equipped with the laser interferometer measures the displacement of the movable mirror; The spectroscopic device is characterized in that the spectroscopic analysis unit generates the spectroscopic spectrum information based on a measurement result of the displacement of the movable mirror by the laser interferometer.

Images