Interferometer

Abstract

To provide an interferometer including a moving mirror that sufficiently tolerates the shift of light produced when the moving mirror is moved while avoiding the use of a large drive unit.SOLUTION: An interferometer comprises: an analysis optical system including a retroreflector configured to reflect analysis light and a first light receiver configured to receive the analysis light and output a first light reception signal, the analysis optical system irradiating a sample with the analysis light and causing the analysis light to interfere; a length measuring optical system including a laser light source configured to output laser light, an optical modulator configured to modulate a frequency of the laser light by using a vibrator and add a modulation component to the laser light, and a second light receiver configured to receive the laser light containing the modulation component and a length measurement component generated when the retroreflector is irradiated with the laser light and output a second light reception signal, the length measuring optical system causing the laser light to interfere; and a drive unit configured to change a position of the retroreflector.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an interferometer. [Background technology]

[0002] Patent Document 1 discloses an optical module used in spectroscopic analysis for acquiring spectral information of light emitted or absorbed by a sample and analyzing components in the sample based on the information. This optical module includes a mirror unit, a beam splitter unit, a light input unit, a first photodetector, a second light source, and a second photodetector. The mirror unit includes a movable mirror that moves in a predetermined direction and a fixed mirror whose position is fixed. In such an optical module, the beam splitter unit, the movable mirror, and the fixed mirror form an interference optical system into which the measurement light and the laser light are respectively input.

[0003] The measurement light incident from the first light source through the measurement object passes through the light incident section and is split by the beam splitter unit. A part of the split measurement light is reflected by the movable mirror and returns to the beam splitter unit. The remaining part of the split measurement light is reflected by the fixed mirror and returns to the beam splitter unit. The part of the measurement light that returned to the beam splitter unit and the remaining part are detected by the first photodetector as interference light.

[0004] Meanwhile, the laser light emitted from the second light source is split by the beam splitter unit. A part of the split laser light is reflected by the movable mirror and returns to the beam splitter unit. The remaining part of the split laser light is reflected by the fixed mirror and returns to the beam splitter unit. The part of the laser light that returned to the beam splitter unit and the remaining part are detected by the second photodetector as interference light.

[0005] In such an optical module, the position of the movable mirror is measured based on the detection result of the interference light of the laser light. Then, based on the measurement result of the position of the movable mirror and the detection result of the interference light of the measurement light, spectroscopic analysis of the measurement object becomes possible. Specifically, by determining the intensity of the measurement light at each position of the movable mirror, a waveform called an interferogram is obtained. By Fourier transforming this interferogram, it is possible to obtain spectral information about the measurement object. Therefore, the optical module described in Patent Document 1 is used in an FTIR (Fourier transform infrared spectroscopic analyzer). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 009404 Summary of the Invention [Problem to be solved by the invention]

[0007] In the optical module described in Patent Document 1, the movable mirror is driven by an electrostatic actuator. In order to obtain highly accurate spectral information, it is important that the light incident on and emitted from the movable mirror is not displaced in a direction perpendicular to the propagation direction as the movable mirror is driven, in other words, that the blur is small. For this reason, it is required to improve the translational movement of the movable mirror. However, in the optical module described in Patent Document 1, the translational movement of the movable mirror is not sufficiently taken into consideration, and there is room for further study.

[0008] On the other hand, ensuring a sufficient amount of movement of the movable mirror is important in that it allows for high wavelength resolution (wavenumber resolution) of the acquired spectral information. However, in order to ensure a sufficient amount of movement while increasing the translational ability of the movable mirror, it is necessary to increase the size of the drive unit that drives the movable mirror.

[0009] Therefore, the realization of an interferometer equipped with a movable mirror that has sufficient tolerance for vibration during movement while suppressing an increase in the size of the drive unit has become an issue. [Means for solving the problem]

[0010] The interferometer according to an application example of the present invention includes: an analytical optical system having a retroreflection unit that reflects the analytical light and a first light receiving element that receives the analytical light and outputs a first light receiving signal, the analytical optical system irradiating the sample with the analytical light and causing interference with the analytical light; A length measurement optical system that includes a laser light source that emits laser light, an optical modulator that modulates the frequency of the laser light using a vibration element and adds a modulated component, and a second light receiving element that receives the laser light including the length measurement component and the modulated component generated by irradiating the laser light to the retroreflection portion and outputs a second light receiving signal, and performs interference of the laser light; A drive unit that changes the position of the retroreflective unit; Equipped with. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram showing a spectroscopic device as an interferometer according to a first embodiment. [Diagram 2] 2 is a schematic diagram showing the configuration of each main part of an analysis unit, a length measurement unit, a periodic signal generation unit and a calculation unit in FIG. 1. [Diagram 3] 2 is a perspective view showing a configuration example of the vibration element shown in FIG. 1. [Figure 4] 1. FIG. 4 is a perspective view showing another configuration example of the vibration element shown in FIG. [Diagram 5] 2 is a diagram showing an example of a first received light signal F(t) and a movable mirror position signal X(t) acquired by the spectroscopic device shown in FIG. 1. FIG. [Figure 6] FIG. 2 is a diagram showing an example of an interferogram F(x). [Figure 7] 1 is an example of a spectral pattern SP0 obtained by performing spectroscopic analysis on a sample. [Figure 8]FIG. 2 is a side view showing an example of the corner cube prism in FIG. [Figure 9] 9 is a plan view of the retroreflective surface of FIG. 8. [Figure 10] FIG. 11 is a side view showing a corner cube mirror that is provided as a movable mirror in a modified example of the first embodiment. [Figure 11] 13 is a side view showing a corner cube prism provided as a movable mirror in the second embodiment. FIG. [Figure 12] FIG. 11 is a side view showing a corner cube mirror that is provided as a movable mirror in a modified example of the second embodiment. [Figure 13] FIG. 11 is a schematic configuration diagram showing a spectroscopic device as an interferometer according to a third embodiment. [Figure 14] FIG. 13 is a schematic configuration diagram showing a shape measuring instrument as an interferometer according to a fourth embodiment. [Figure 15] 15 is a schematic diagram showing the configuration of each main part of an analysis section, a length measurement section, a periodic signal generation section and a calculation section in FIG. 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an interferometer according to the present invention will be described in detail based on an embodiment shown in the accompanying drawings. 1. First embodiment First, the interferometer according to the first embodiment will be described.

[0013] Fig. 1 is a schematic diagram showing a spectroscopic device 100 as an interferometer according to the first embodiment. Fig. 2 is a schematic diagram showing the main parts of the analysis unit 300, the length measurement unit 400, the periodic signal generation unit 6 and the calculation unit 7 shown in Fig. 1.

[0014] In the spectroscopic device 100 shown in FIG. 1, the incident analytical light L1 is irradiated onto a sample 9, which is an object of the test, and the analytical light L1 emitted from the sample 9 is passed through a Michelson type interference optical system. Then, a movable mirror is moved to change the optical path length inside the interference optical system, and the intensity change of the obtained interference light is detected, and an interferogram is obtained by performing a calculation on the result. A spectrum pattern (spectral information) including information derived from the sample 9 is obtained by Fourier transforming the obtained interferogram. By selecting the wavelength of the analytical light L1, the spectroscopic device 100 shown in FIG. 1 can be applied to, for example, FT-IR (Fourier type infrared spectroscopy), FT-NIR (Fourier type near infrared spectroscopy), FT-VIS (Fourier type visible spectroscopy), FT-UV (Fourier type ultraviolet spectroscopy), FT-THz (Fourier type terahertz spectroscopy), etc. for the sample 9.

[0015] As shown in FIG. 1, the spectroscopic device 100 includes an analysis section 300 having an analysis optical system 3 and a drive section 8, a length measurement section 400 having a length measurement optical system 4, a periodic signal generation section 6, and a calculation section .

[0016] The analytical optical system 3 irradiates the sample 9 with the analytical light L1, and splits and mixes the analytical light L1 to generate interference while changing the optical path length of the analytical light L1 so that sample-derived components originating from the sample 9 can be extracted from the analytical light L1. The length measurement optical system 4 measures the change in the optical path length of the analytical light L1 using the length measurement light L2, which is a laser beam.

[0017] The periodic signal generating unit 6 outputs a reference signal Ss to the calculation unit 7. The calculation unit 7 obtains a waveform representing the intensity of the interference light relative to the optical path length, i.e., the above-mentioned interferogram, based on the signal representing the intensity of the interference light output from the analysis optical system 3 and the signal representing the change in the optical path length output from the length measurement optical system 4. The calculation unit 7 also performs a Fourier transform on the interferogram to obtain a spectral pattern.

[0018] 1.1.Analysis optical system The analytical optical system 3 includes a first light source 51, a beam splitter 54, a condenser lens 55, and a neutral density filter 56. Note that in the analytical optical system 3, some of these optical elements may be omitted, or other optical elements may be included, or these optical elements may be replaced with other optical elements.

[0019] The first light source 51 is a light source that emits, for example, white light, that is, light that is a collection of light of a wide wavelength range, as the analytical light L1. The wavelength range of the analytical light L1, that is, the type of the first light source 51, is appropriately selected according to the purpose of the spectroscopic analysis performed on the sample 9. When infrared spectroscopic analysis is performed, examples of the first light source 51 include a halogen lamp, an infrared lamp, a tungsten lamp, etc. When visible spectroscopic analysis is performed, examples of the first light source 51 include a halogen lamp, etc. When ultraviolet spectroscopic analysis is performed, examples of the first light source 51 include a deuterium lamp, a UV-LED (ultraviolet light emitting diode), etc.

[0020] By selecting a wavelength of the analytical light L1 that is equal to or greater than 100 nm and less than 760 nm, it is possible to realize a spectroscopic device 100 that can perform ultraviolet spectroscopic analysis or visible spectroscopic analysis. By selecting a wavelength of the analytical light L1 that is equal to or greater than 760 nm and less than 20 μm, it is possible to realize a spectroscopic device 100 that can perform infrared spectroscopic analysis or near-infrared spectroscopic analysis. Furthermore, by selecting a wavelength of the analytical light L1 that is equal to or greater than 30 μm and less than 3 mm, it is possible to realize a spectroscopic device 100 that can perform terahertz wave spectroscopic analysis.

[0021] The first light source 51 may be provided outside the spectroscopic device 100. In this case, it is only necessary that the analytical light L1 emitted from the externally provided first light source 51 is introduced into the spectroscopic device 100. Meanwhile, by providing the spectroscopic device 100 with the first light source 51 as in this embodiment, it is possible to particularly improve the alignment accuracy between the first light source 51 and the beam splitter 54, and to minimize the loss of the analytical light L1 due to poor alignment.

[0022] The first light source 51 may be a laser light source that emits laser light. By using a laser light source as the first light source 51, a spectroscopic device 100 capable of performing laser excitation spectroscopic analysis such as Fourier Raman spectroscopic analysis and Fourier fluorescence spectroscopic analysis on the sample 9 can be obtained. In this case, the configuration of the analytical optical system 3 may be changed from the above configuration. In this case, a known light source used for Raman spectroscopy or fluorescence spectroscopy is used as the laser light source.

[0023] The analytical light L1 passes through the beam splitter 54, is collected by the collecting lens 55, and is irradiated onto the sample 9. The analytical light L1 is reflected by the sample 9 and returns to the beam splitter 54. This enables spectroscopic analysis based on the reflected light emitted from the sample 9, i.e., analysis by reflection spectroscopy. Note that by changing the optical path of the analytical optical system 3, analysis by transmission spectroscopy becomes possible.

[0024] Although a non-polarizing beam splitter, for example, is used as the beam splitter 54, a polarizing beam splitter may also be used. In this case, a necessary wave plate may be added appropriately.

[0025] The condenser lens 55 condenses the analytical light L1 to reduce the spot size of the analytical light L1 irradiated on the sample 9. The condenser lens 55 also condenses the diffused light emitted from the sample 9. This enables local analysis. If local analysis is not required, the condenser lens 55 may be omitted.

[0026] The analytical light L1 emitted from the sample 9 contains sample-derived components generated by the action of the sample 9. The sample-derived components are components generated by the action of the analytical light L1 on the sample 9, and examples of the action include light absorption, reflection, scattering, and emission of a specific wavelength by the sample 9. This analytical light L1 passes through a condenser lens 55, is reflected by a beam splitter 54, and passes through a neutral density filter 56. The neutral density filter 56 selectively attenuates light of a specific wavelength. This makes it possible to increase the S / N ratio (signal-to-noise ratio) of the sample-derived components, and to perform spectroscopic analysis with higher accuracy. An example of the neutral density filter 56 is a notch filter with an optical density (OD value) of 6.0 or more.

[0027] The analytical optical system 3 also includes a beam splitter 32 (light splitting section), a movable mirror 33 (retroreflection section), a fixed mirror 34 (fixed reflection section), a condenser lens 35, and a first light receiving element 36, which constitute a Michelson type interference optical system. Note that the analytical optical system 3 may omit some of these optical elements, may include optical elements other than these, or may replace these optical elements with other optical elements.

[0028] The beam splitter 32 is a non-polarizing beam splitter that splits the analytical light L1 into two analytical lights L1a and L1b. Specifically, the beam splitter 32 splits the analytical light L1 into two by reflecting a part of the analytical light L1 toward a movable mirror 33 as analytical light L1a and transmitting the other part of the analytical light L1 toward a fixed mirror 34 as analytical light L1b.

[0029] The beam splitter 32 may be of a type such as a prism-type element (cube-type element) shown in FIG. 1, a plate-type element, a laminated element, or the like. When the plate-type beam splitter 32 is used, wavelength dispersion occurs between the analytical light L1a and the analytical light L1b, so a wavelength dispersion compensation plate may be disposed between the beam splitter 32 and the fixed mirror 34 as necessary. The wavelength dispersion compensation plate is an optical element that compensates for wavelength dispersion caused by the optical path length difference of glass materials. In this embodiment, a prism-type element is used as the beam splitter 32, so this wavelength dispersion compensation plate is not required. The prism-type element is an element in which an optical thin film is sandwiched between prisms. The laminated element is an element in which an optical thin film is sandwiched between two transparent flat plates. The laminated element can also eliminate the need for a wavelength dispersion compensation plate, as in the case of the prism-type element. In addition, in the prism-type element and the laminated element, the optical thin film is not exposed, so that the long-term reliability of the beam splitter 32 can be improved.

[0030] Moreover, the beam splitter 32 transmits the analytical light L1a reflected by the movable mirror 33 toward the first light receiving element 36, and reflects the analytical light L1b reflected by the fixed mirror 34 toward the first light receiving element 36. Thus, the beam splitter 32 mixes the split analytical light L1a, L1b.

[0031] The movable mirror 33 is a mirror that moves in the incident direction of the analytical light L1a relative to the beam splitter 32 and reflects the analytical light L1a. The movable mirror 33 is moved back and forth in the incident direction of the analytical light L1a by the driver 8. The analytical light L1a reflected by the movable mirror 33 changes in phase depending on the position of the movable mirror 33. As a result, the movable mirror 33 adds phase information derived from the position of the movable mirror 33 to the analytical light L1a. The phase information derived from the position of the movable mirror 33 is a change in phase added to the analytical light L1a depending on the position of the movable mirror 33.

[0032] The movable mirror 33 (retroreflecting section) has a corner cube prism 330. The corner cube prism 330 is also called a retroreflector prism, and has a function of retroreflecting light incident at a predetermined range of incident angles and returning it to the incident direction. In this specification, such a function is called "retroreflectivity". By using an optical element having retroreflectivity as the movable mirror 33, the tolerance of blurring that occurs when the movable mirror 33 moves can be increased compared to the case where a flat mirror is used. In other words, even if an angle deviation (deviation angle) occurs due to blurring when the movable mirror 33 moves, the effect of the angle deviation can be reduced, and the effect on the analysis result can be suppressed. Note that when a flat mirror is used, retroreflection occurs only when the incident angle is 0°, but in an optical element having retroreflectivity such as the corner cube prism 330, retroreflection occurs even when the incident angle is more than 0°.

[0033] The corner cube prism 330 retroreflects the analytical light L1a and returns it to the beam splitter 32 via an exit path parallel to the entrance path. In addition, due to retroreflectivity, the exit path does not change even if the movable mirror 33 shakes during movement. By utilizing this characteristic, the mixed state of the analytical light L1a, L1b in the beam splitter 32 can be kept constant. As a result, it is possible to suppress a decrease in the S / N ratio of the interference signal of the analytical light L1a, L1b that is caused by the shaking of the movable mirror 33 during movement, and to suppress the impact on the analysis result. The corner cube prism 330 will be described in detail later.

[0034] Furthermore, by increasing the tolerance for blurring that occurs when the movable mirror 33 moves, it is possible to lower the priority of the driving accuracy of the driver 8. Therefore, even if the amount of movement of the movable mirror 33 by the driver 8 is sufficiently ensured, a small driver 8 can be used. This allows the spectroscopic device 100 to be made smaller, lighter, and less expensive.

[0035] The fixed mirror 34 is a mirror whose position is fixed with respect to the beam splitter 32 and reflects the analytical light L1b. The analytical light L1b reflected by the fixed mirror 34 is mixed with the analytical light L1a by the beam splitter 32 and is received by the first light receiving element 36 as interference light. In the analytical optical system 3, an optical path difference occurs between the optical path of the analytical light L1a and the optical path of the analytical light L1b depending on the position of the movable mirror 33. The fixed mirror 34 may be a flat mirror, a corner cube prism, or a corner cube mirror. The fixed mirror 34 shown in FIG. 1 is composed of a roof mirror formed by combining two flat mirrors 341 and 342. Among these, by using a corner cube prism, a corner cube mirror, a roof mirror, or the like having retroreflective properties as the fixed mirror 34, it is possible to suppress a decrease in the S / N ratio of the interference signal caused by an angular deviation (angle of deviation) of the arrangement of the fixed mirror 34, and to suppress the influence on the analysis result.

[0036] The condenser lens 35 condenses the interference light, that is, the mixed analytical light L1a, L1b, onto the first light receiving element 36. Depending on the area of ​​the light receiving portion of the first light receiving element 36, the condenser lens 35 may be omitted.

[0037] The first light receiving element 36 receives the interference light and acquires its intensity. Then, a signal indicating the change in intensity over time is output as a first light receiving signal F(t). This first light receiving signal F(t) includes a sample-derived component generated by the interaction between the analytical light L1 and the sample 9, and phase information derived from the position of the movable mirror 33 described above.

[0038] The first light receiving element 36 may be, for example, a photodiode, a phototransistor, a photomultiplier tube (PMT), etc. Among these, the photodiode may be, for example, an InGaAs-based photodiode, a Si-based photodiode, an avalanche photodiode, etc.

[0039] 1.2. Length measurement optical system The length measurement optical system 4 is a Michelson type interference optical system, and includes a second light source 41, a beam splitter 42, an optical modulator 12, a second light receiving element 45, a half-wave plate 46, a half-wave plate 47, a quarter-wave plate 48, an analyzer 49, optical path changing mirrors 441, 442, 443, 444, and a beam splitter 445. In the length measurement optical system 4, some of these optical elements may be omitted, other optical elements may be included, or these optical elements may be replaced with other optical elements. The length measurement optical system 4 outputs phase information derived from the position of the moving mirror 33 and frequency information derived from the moving speed to the calculation unit 7 by optical heterodyne interferometry. In this specification, these pieces of information are referred to as "length measurement components".

[0040] A light source that emits light with a narrow spectral line width is preferably used as the second light source 41. Examples of the second light source 41 include gas lasers such as He-Ne lasers and Ar lasers, 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), and crystal lasers such as YAG (Yttrium Aluminum Garnet).

[0041] It is particularly preferable that the second light source 41 is a semiconductor laser element, which allows the spectroscopic device 100 to be made smaller, lighter, and consume less power.

[0042] The beam splitter 42 is a polarizing beam splitter that transmits P polarized light and reflects S polarized light. The half-wave plate 46 is disposed with its optical axis rotated with respect to the polarization axis of the measurement light L2. As a result, when the measurement light L2 passes through the half-wave plate 46, it becomes linearly polarized light containing P polarized light and S polarized light, and is split by the beam splitter 42 into two, P polarized light and S polarized light.

[0043] The measurement light L2a, which is S-polarized light, is converted into circularly polarized light by the quarter-wave plate 48 and enters the optical modulator 12. The optical modulator 12 adds a modulation component to the measurement light L2a by reflecting the measurement light L2a. The modulation component is a change in frequency that occurs when the measurement light L2a is reflected by the vibration element 30. The reflected measurement light L2a returns to the beam splitter 42. At this time, the measurement light L2a is converted into P-polarized light by the quarter-wave plate 48.

[0044] On the other hand, the P-polarized measurement light L2b is converted to S-polarized light by the half wavelength plate 47 and enters the movable mirror 33 via the optical path changing mirrors 441 and 442. The measurement light L2b is guided to the optical path changing mirrors 441 and 442 and enters the movable mirror 33 on the same entrance surface as the analysis light L1a. The movable mirror 33 reflects the measurement light L2b. As a result, the phase of the measurement light L2b changes depending on the position of the movable mirror 33. The measurement light L2b reflected by the movable mirror 33 enters the beam splitter 445 via the optical path changing mirrors 443 and 444.

[0045] In this embodiment, as described above, the analytical light L1a and the measurement light L2b are incident on the same incident surface of the movable mirror 33. In this case, the phase information added to the analytical light L1a and the phase information added to the measurement light L2b are information derived from the position of the same reflecting surface of the movable mirror 33. This makes it possible to further increase the correlation between the two pieces of phase information, thereby improving the accuracy of the ultimately obtained analysis results.

[0046] Furthermore, the beam splitter 42 transmits the measurement light L2a returning from the optical modulator 12 toward the beam splitter 445. The beam splitter 445 is a polarizing beam splitter, and mixes the measurement light L2a emitted from the beam splitter 42 with the measurement light L2b reflected by the movable mirror 33. The mixed measurement light L2a, L2b passes through the analyzer 49 and enters the second light receiving element 45.

[0047] As the optical modulator 12, for example, the optical modulator disclosed in JP 2022-38156 A can be mentioned. In this embodiment, the optical modulator 12 has a vibration element 30. The vibration element 30 vibrates by the element drive signal Sd and reflects the length measurement light L2a. As a result, the optical modulator 12 superimposes a modulation component on the length measurement light L2a.

[0048] Examples of the vibration element 30 include a quartz crystal vibrator, a silicon vibrator, and a ceramic vibrator. These vibrators utilize the mechanical resonance phenomenon, and therefore have a high Q value and can easily stabilize the natural frequency. This can increase the S / N ratio of the modulated component that the optical modulator 12 applies to the measurement light L2a, and can also increase the accuracy of the reference signal Ss. As a result, the position of the movable mirror 33 can be determined with high accuracy, and ultimately, a spectrometer 100 can be realized that can generate a spectral pattern with high accuracy on the wavelength axis (wave number axis).

[0049] Examples of the quartz crystal resonator include a quartz crystal AT resonator, an SC cut quartz crystal resonator, a tuning fork type quartz crystal resonator, a quartz crystal surface acoustic wave element, etc. The oscillation frequency of the quartz crystal resonator is, for example, about 1 kHz to several hundreds of MHz.

[0050] The 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 a two-legged tuning fork type and a three-legged tuning fork type, and a double-supported beam shape. The oscillation frequency of the silicon vibrator is, for example, about 1 kHz to several hundreds of MHz.

[0051] The ceramic vibrator is a vibrator that includes a piezoelectric ceramic piece manufactured by baking and hardening a piezoelectric ceramic, and an electrode. Examples of the piezoelectric ceramic include lead zirconate titanate (PZT) and barium titanate (BTO). The oscillation frequency of the ceramic vibrator is, for example, about several hundred kHz to several tens of MHz.

[0052] FIG. 3 is a perspective view showing a configuration example of the vibration element 30 shown in FIG. The vibration element 30 shown in FIG. 3 includes a plate-shaped vibration piece 431 and a diffraction grating 434 provided on the vibration piece 431.

[0053] The vibrating bar 431 is made of a material that repeats a mode of vibration in which the vibrating bar is distorted in a direction along the surface when a potential is applied. The vibrating bar 431 shown in FIG. 3 is a quartz crystal AT vibrator that vibrates in a thickness-shear manner along a vibration direction 436 in a high frequency region of the MHz band. A diffraction grating 434 is provided on the surface of the vibrating bar 431. The diffraction grating 434 has grooves 432 having a component intersecting with the vibration direction 436, that is, a plurality of linear grooves 432 extending in a direction intersecting with the vibration direction 436.

[0054] The vibrating bar 431 has a front surface 4311 and a back surface 4312 which are in a front-back relationship. A diffraction grating 434 is disposed on the front surface 4311. A pad 433 for applying a potential to the vibrating bar 431 is also provided on the front surface 4311. Meanwhile, a pad 435 for applying a potential to the vibrating bar 431 is also provided on the back surface 4312.

[0055] The size of the vibrating bar 431 is, for example, about 0.50 mm or more and 10.0 mm or less in terms of the long side. The thickness of the vibrating bar 431 is, for example, about 0.10 mm or more and 2.0 mm or less. As an example, the shape of the vibrating bar 431 is a square with one side measuring 1.6 mm, and the thickness is 0.35 mm.

[0056] The size of the diffraction grating 434 is, for example, about 0.20 mm or more and 3.0 mm or less in terms of the long side, and the thickness of the diffraction grating 434 is, for example, about 0.003 mm or more and 0.50 mm or less.

[0057] In this embodiment, the vibrating bar 431 vibrates in a thickness-shear manner, but since this vibration is an in-plane vibration as shown by vibration direction 436 in Fig. 3, light cannot be modulated even if light is incident perpendicularly to the surface of the vibrating bar 431 alone. Therefore, in the vibrating element 30, a diffraction grating 434 is provided on the vibrating bar 431, thereby enabling light modulation.

[0058] Diffraction grating 434 shown in Fig. 3 is a blazed diffraction grating as an example. A blazed diffraction grating is a diffraction grating whose cross-sectional shape is stepped. Note that the shape of diffraction grating 434 is not limited to this.

[0059] 4 is a perspective view showing another example of the configuration of the vibration element 30 shown in FIG. 1. In FIG. 4, an A-axis, a B-axis, and a C-axis are set as three mutually orthogonal axes, and are indicated by arrows. The tip end side of the arrow is designated as "plus" and the base end side of the arrow is designated as "minus". For example, both the plus side and the minus side of the A-axis are referred to as "A-axis directions". The same is true for the B-axis and C-axis directions.

[0060] The vibration element 30 shown in Fig. 4 is a tuning fork type crystal vibrator. The vibration element 30 shown in Fig. 4 has a vibration substrate having a base 401, a first vibrating arm 402 and a second vibrating arm 403. Such tuning fork type crystal vibrators are easily available because of established manufacturing techniques, and the oscillation is stable. For this reason, the tuning fork type crystal vibrator is suitable as the vibration element 30. The vibration element 30 also has electrodes 404, 405 and a light reflecting surface 406 provided on the vibration substrate.

[0061] 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.

[0062] The electrodes 404 are conductive films provided on the side surfaces parallel to the AB plane of the first vibrating arm 402 and the second vibrating arm 403. Although not shown in Fig. 4, the electrodes 404 are provided on the opposing side surfaces, and drive the first vibrating arm 402 and the second vibrating arm 403 by applying voltages of different polarities to each other.

[0063] The electrodes 405 are conductive films provided on the side surfaces intersecting with the AB plane of the first vibrating arm 402 and the second vibrating arm 403. Although not shown in Fig. 4, the electrodes 405 are also provided on the opposing side surfaces, and drive the first vibrating arm 402 and the second vibrating arm 403 by applying voltages of different polarities to each other.

[0064] The light reflecting surface 406 is set on the side surfaces of the first vibrating arm 402 and the second vibrating arm 403 that intersect with the AB plane, and has a function of reflecting the measurement light L2a. The side surfaces refer to surfaces that extend along the extension direction of the first vibrating arm 402 and the second vibrating arm 403. The light reflecting surface 406 shown in FIG. 4 is set on the side surfaces of the first vibrating arm 402, particularly on the surface of the electrode 405. The electrode 405 provided on the first vibrating arm 402 also functions as the light reflecting surface 406. Note that a light reflecting film (not shown) may be provided separately from the electrode 405.

[0065] For the tuning fork type quartz crystal resonator, a quartz crystal piece cut out from a quartz crystal substrate is used. Examples of the quartz crystal substrate used in the manufacture of the tuning fork type quartz crystal resonator include a quartz crystal Z-cut flat plate. In FIG. 4, an X-axis parallel to the A-axis, a Y'-axis parallel to the B-axis, and a Z'-axis parallel to the C-axis are set. The quartz crystal Z-cut flat plate is a substrate cut out from a single crystal of quartz 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 an orthogonal coordinate system consisting of the X-axis, Y'-axis, and Z'-axis, a substrate having a main surface tilted counterclockwise about the X-axis by about 1° to 5° from the X-Y' plane consisting of the X-axis and Y'-axis is cut out from a single crystal of quartz crystal and is preferably used as the quartz crystal substrate. Then, by etching such a quartz crystal substrate, a quartz crystal piece used in the vibration element 30 shown in FIG. 4 is obtained. The etching may be wet etching or dry etching.

[0066] On the other hand, the light reflecting surface 406 may be set on the surface of the electrode 404. In this case, the signal applied to each electrode may be adjusted so that the tuning fork crystal resonator vibrates out of plane, specifically, so that the signal is excited in an out of plane vibration mode (including spurious components).

[0067] The second light receiving element 45 receives the mixed length measurement light L2a, L2b as interference light, and obtains its intensity. Then, a signal indicating the time change of the intensity is output as a second light receiving signal S2. This second light receiving signal S2 includes a length measurement component derived from the position of the movable mirror 33.

[0068] The second light receiving element 45 may be, for example, a photodiode or a phototransistor.

[0069] The optical elements of each optical system have been described above, but it is preferable that the optical elements that require light to be incident thereon are subjected to an anti-reflection treatment, which can increase the S / N ratio of the first light receiving signal F(t) and the second light receiving signal S2.

[0070] 1.3. Periodic signal generation section 2 generates a periodic signal and outputs it as a reference signal Ss. In this embodiment, the periodic signal generating unit 6 has an oscillation circuit 62.

[0071] An example of the oscillator circuit 62 is the oscillator circuit disclosed in JP 2022-38156 A. The oscillator circuit 62 operates with the vibration element 30 as a signal source to generate a highly accurate periodic signal. As a result, the oscillator circuit 62 outputs a highly accurate element drive signal Sd and reference signal Ss. Then, when the element drive signal Sd and the reference signal Ss are subjected to a disturbance, they are affected by each other in the same way. As a result, the modulation component added via the vibration element 30 driven by the element drive signal Sd and the reference signal Ss are also affected by each other in the same way. Therefore, when the second light receiving signal S2 and the reference signal Ss are subjected to the calculation in the calculation unit 7, the effects of the disturbances contained in both can be offset or reduced by each other during the calculation. As a result, the calculation unit 7 can accurately determine the position of the moving mirror 33 even when disturbances are received.

[0072] The oscillator circuit disclosed in the above publication is a circuit using an inverter IC, but a Colpitts oscillator circuit may be used instead.

[0073] 1.4.Drive unit 1 has a motor M and a power conversion unit 862. The motor M generates a rotation output, and the power conversion unit 862 converts the rotation output into linear motion to drive the moving mirror 33.

[0074] The motor M generates a rotation output in a predetermined rotation direction and at a predetermined rotation speed. Examples of the motor M include a stepping motor, a brushless motor, and an ultrasonic (piezo) motor.

[0075] The power conversion unit 862 converts the rotation output into linear motion. In addition, when the motor M generates a linear output, the power conversion unit 862 may be omitted. For example, the power conversion unit 862 may be a mechanism including various gears and a linear guide. Such a mechanism can easily increase the amount of movement compared to, for example, a MEMS (Micro Electro Mechanical Systems) mechanism. Therefore, the wavelength resolution (wave number resolution) of the spectrum pattern that can be acquired can be easily increased. In addition, by using a linear guide, the translational property of the movable mirror 33 can be improved. The translational property refers to the property of moving linearly without changing the posture of the movable mirror 33 as much as possible.

[0076] 1.5. Arithmetic section The calculation unit 7 shown in Fig. 2 has a moving mirror position calculation unit 72, a light intensity calculation unit 74, and a Fourier transform unit 76. The functions performed by these functional units are realized by hardware including, for example, a processor, a memory, an external interface, an input unit, a display unit, and the like. Specifically, the functions are realized by the processor reading and executing a program stored in the memory. These components are capable of communicating with each other via an external bus.

[0077] Examples of the processor include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. Note that instead of using these processors to execute software, a system in which a FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc., realizes the above-mentioned functions may be adopted.

[0078] Examples of memory include HDD (Hard Disk Drive), SSD (Solid State Drive), EEPROM (Electrically Erasable Programmable Read-Only Memory), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0079] Examples of the external interface include a digital input / output port such as a Universal Serial Bus (USB), an Ethernet (registered trademark) port, and the like.

[0080] Examples of the input unit include various input devices such as a keyboard, a mouse, a touch panel, a touch pad, etc. Examples of the display unit include a liquid crystal display panel, an organic EL (Electro Luminescence) display panel, etc. Note that the input unit and the display unit may be provided as necessary, and may be omitted.

[0081] 1.5.1. Moving mirror position calculation unit The movable mirror position calculation unit 72 shown in FIG. 2 identifies the position of the movable mirror 33 by optical heterodyne interferometry, and generates a movable mirror position signal X(t) based on the result. Specifically, the length measurement optical system 4 includes an optical modulator 12, so that a modulated component can be added to the length measurement light L2a. When the length measurement light L2a and L2b are made to interfere with each other, the length measurement component originating from the position of the movable mirror 33 can be obtained with high accuracy from the obtained interference light. The calculation unit 7 can then obtain the movable mirror position signal X(t) with high accuracy based on the length measurement component. According to the optical heterodyne interferometry, when extracting the length measurement component, it is less susceptible to the influence of disturbances, particularly stray light of a frequency that becomes noise, and high robustness is provided.

[0082] 2 has a pre-processing unit 722, a demodulation processing unit 724, and a moving mirror position signal output unit 726. For example, the pre-processing unit and the demodulation processing unit 724 disclosed in JP 2022-38156 A can be applied to the pre-processing unit 722 and the demodulation processing unit 724.

[0083] The pre-processing unit 722 performs pre-processing on the second received light signal S2 based on the reference signal Ss. The demodulation processing unit 724 demodulates the length measurement component derived from the position of the movable mirror 33 based on the reference signal Ss from the pre-processed signal output from the pre-processing unit 722. In other words, the demodulation processing unit 724 demodulates the length measurement component based on the reference signal Ss, which is a periodic signal generated by the periodic signal generating unit 6, and the second received light signal S2.

[0084] The moving mirror position signal output unit 726 generates and outputs a moving mirror position signal X(t) based on the measurement components derived from the moving mirror 33 demodulated by the demodulation processing unit 724. The moving mirror position signal X(t) obtained in this manner is a signal representing the position of the moving mirror 33 which changes with time, and captures the displacement of the moving mirror 33 at intervals sufficiently narrower than the wavelength of the measurement light L2. For example, when the wavelength of the measurement light L2 is several hundreds of nm, it is possible to achieve a position resolution of less than 10 nm for the moving mirror position signal X(t). Therefore, the light intensity calculation unit 74 can generate highly accurate digital data of the interferogram F(x).

[0085] Fig. 5 is a diagram showing an example of the first light receiving signal F(t) and the movable mirror position signal X(t) acquired by the spectroscopic device 100 shown in Fig. 1. The horizontal axis of Fig. 5 represents time t, and the vertical axis represents the intensity of the interference light incident on the first light receiving element 36 or the position of the movable mirror 33.

[0086] The movable mirror position signal X(t) shown in FIG. 5 is a signal that continuously detects changes in the position of the movable mirror 33 and achieves high position resolution. Therefore, by generating an interferogram F(x) based on this signal, an interferogram F(x) with a larger number of data points can be obtained. A larger number of data points means that the sampling interval of the interferogram F(x) is short and the accuracy is high. Therefore, by using the interferogram F(x) obtained in this manner, a spectral pattern with high wavelength resolution (wavenumber resolution) can be ultimately obtained.

[0087] Furthermore, by shortening the sampling interval, it is possible to obtain an interferogram F(x) with a sufficient number of data points even when using analytical light L1 with a shorter wavelength (larger wavenumber). This makes it possible to obtain a spectral pattern over a wider wavelength range (wider wavenumber range), i.e., a broader band spectral pattern.

[0088] 1.5.2.Light Intensity Calculation Unit The light intensity calculator 74 generates a waveform (interferogram F(x)) that represents the intensity of the interference light with respect to the position of the movable mirror 33, based on the first light receiving signal F(t) and the movable mirror position signal X(t).

[0089] As described above, the first light receiving signal F(t) contains phase information derived from the sample-derived components and the movable mirror 33. The light intensity calculation unit 74 extracts the intensity of the first light receiving signal F(t) based on the movable mirror position signal X(t). The light intensity calculation unit 74 then generates an interferogram F(x) based on the position of the movable mirror 33 determined from the movable mirror position signal X(t) and the intensity of the first light receiving signal F(t). The interferogram F(x) is expressed as a function of the optical path difference between the reflected light at the movable mirror 33 and the reflected light at the fixed mirror 34 in the analysis optical system 3, and the intensity of the interference light received by the first light receiving element 36 (the intensity of the first light receiving signal F(t)).

[0090] Fig. 6 is a diagram showing an example of an interferogram F(x). The horizontal axis of Fig. 6 represents the optical path difference of the analytical optical system 3, and the vertical axis represents the intensity of the interference light. Note that the optical path difference of the analytical optical system 3 is the difference between the optical path length between the beam splitter 32 and the movable mirror 33 and the optical path length between the beam splitter 32 and the fixed mirror 34, and in Fig. 6, the origin of the horizontal axis is set to zero optical path difference.

[0091] 1.5.3.Fourier transform section The Fourier transform unit 76 performs a Fourier transform on the interferogram F(x), thereby acquiring a spectral pattern including information specific to the sample 9.

[0092] 7 shows an example of a spectral pattern SP0 obtained by performing spectroscopic analysis on the sample 9. The spectral pattern SP0 is an example of the reflection spectrum of the sample 9.

[0093] 7, components derived from the sample 9 that are generated when the analytical light L1 acts on the sample 9 are reflected as absorption peaks X9. The spectroscopic device 100 can analyze the characteristics of the sample 9, such as the material, structure, and amounts of components, based on the spectral pattern SP0.

[0094] This spectral pattern SP0 is generated by Fourier transforming the interferogram F(x). Since the interferogram F(x) is an electric field amplitude waveform obtained using the position of the movable mirror 33 as a parameter, the spectral pattern SP0 obtained by Fourier transforming it has wavelength information. The position of the movable mirror 33 is directly linked to the wavenumber accuracy of the spectral pattern SP0. Therefore, according to the spectroscopic device 100 of this embodiment, the position of the movable mirror 33 can be obtained more accurately, so that it is possible to generate a spectral pattern SP0 with high accuracy in the wavelength axis (wavenumber axis). Furthermore, according to this embodiment, it is possible to suppress a decrease in the S / N ratio of the interference signals of the analytical lights L1a and L1b that is caused by the shaking of the movable mirror 33 when it moves, so that the influence of the shaking of the movable mirror 33 on the spectral pattern SP0 can be suppressed.

[0095] 1.6. Corner cube prism Fig. 8 is a side view showing an example of the corner cube prism 330 in Fig. 1. Fig. 9 is a plan view of the retroreflective surface 334 in Fig. 8. In Fig. 8 and Fig. 9, the path of incident light is indicated by arrows. Note that the path of light shown in Fig. 9 has been simplified for convenience of illustration.

[0096] The corner cube prism 330 shown in FIG. 8 has an incident surface 332 and a retroreflective surface 334. The incident surface 332 faces the beam splitter 32 and is configured as a flat surface. When light is incident on the incident surface 332, it enters the corner cube prism 330, is reflected by the retroreflective surface 334, and is emitted again from the incident surface 332. The retroreflective surface 334 includes three surfaces 335, 336, and 337 shown in FIG. 9. These three surfaces 335, 336, and 337 form the corners of a cube (cube), and cause three internal reflections. This allows the light emitted from the incident surface 332 to return in the same direction as the incident direction.

[0097] Such a corner cube prism 330 has retroreflectivity not only when the angle of incidence of light with respect to the incident surface 332 is 0°, but also when the angle exceeds 0°. Moreover, the corner cube prism 330 can achieve retroreflectivity with a single component. Therefore, by using the corner cube prism 330, it is possible to easily simplify, reduce the size, weight, and cost of the movable mirror 33.

[0098] Considering the optical paths formed inside the corner cube prism 330, each of the three faces 335, 336, and 337 shown in FIG. 9 is divided into two regions. The face 335 has the regions 335a and 335b, the face 336 has the regions 336a and 336b, and the face 337 has the regions 337a and 337b. The light incident on the corner cube prism 330 is reflected by three of these six regions and emitted. Therefore, the corner cube prism 330 forms three optical paths that are different from each other. For example, the analysis light L1a is incident on the incident face 332, and then reflected by the regions 335a, 336b, and 337b, respectively, and passes through the optical path LP1 that is emitted from the incident face 332. Moreover, the measurement light L2b is incident on the incident surface 332, and then is reflected by the regions 335b, 337a, and 336a, respectively, and passes through the optical path LP2 emerging from the incident surface 332. By making the analysis light L1a and the measurement light L2b incident so as to follow different optical paths in this way, even when both are reflected by the same retroreflective surface 334, the position where the analysis light L1a is reflected and the position where the measurement light L2b is reflected can be made different. This makes it possible to suppress unintended mixing of the analysis light L1a and the measurement light L2b (mutual signal leakage). As a result, it is possible to suppress the decrease in the S / N ratio of the interference signal described above.

[0099] It is preferable that an anti-reflection film 333 is provided on the incident surface 332 of the corner cube prism 330. This can increase the incidence efficiency of the light (analysis light L1a and measurement light L2b) incident on the incident surface 332. Also, the emission efficiency of the light (analysis light L1a and measurement light L2b) emitted from the incident surface 332 can be increased. Furthermore, the generation of reflected stray light on the incident surface 332 can be suppressed, and the generation of noise caused by the reflected stray light entering the first light receiving element 36 can be suppressed. As a result, the decrease in the S / N ratio of the interference signal can be suppressed. For example, a dielectric multilayer film can be used as the anti-reflection film 333.

[0100] The corner cube prism 330 may be configured so that light undergoes total internal reflection at the retroreflective surface 334. Specifically, in order to cause total internal reflection, the retroreflective surface 334 may be configured to be an interface with a low refractive index medium such as air. This allows the reflectance at the retroreflective surface 334 to approach 100%, thereby increasing the reflection efficiency of the corner cube prism 330.

[0101] The corner cube prism 330 may be configured so that light is specularly reflected by the retroreflective surface 334. Specifically, in order to generate specular reflection, the retroreflective surface 334 may be configured to be an interface with a high refractive index medium such as a metal. This allows the reflectance to be increased regardless of the angle of incidence on the retroreflective surface 334. In addition, in specular reflection, the reflectance does not depend on the polarization, so that losses associated with the polarization dependence of the reflectance can be suppressed. Examples of high refractive index media include metals such as Al, Au, and Ag.

[0102] The movable mirror 33 also has a mounting portion 338 on which the above-mentioned corner cube prism 330 is mounted. The mounting portion 338 shown in FIG. 8 supports the corner cube prism 330 and is driven by the driving portion 8. In other words, the mounting portion 338 only needs to have a function as a slider that is linearly driven by a linear guide of the driving portion 8, for example, and a function as a housing that holds the corner cube prism 330 in the same position. With such a configuration that has the mounting portion 338, a linear guide of a necessary length is provided in the driving portion 8, so that the amount of movement of the movable mirror 33 can be secured to be sufficiently long. This makes it easy to increase the wavelength resolution (wavenumber resolution) of the spectrum pattern that can be acquired.

[0103] In this embodiment, the retroreflective surface 334 is configured to reflect both the analytical light L1a and the measurement light L2b, but the measurement light L2b may be configured to be reflected by a reflective surface that does not have retroreflective properties and is provided separately from the retroreflective surface 334.

[0104] 2. Modification of the First Embodiment Next, a modification of the first embodiment will be described.

[0105] FIG. 10 is a side view showing a corner cube mirror 331 provided as the movable mirror 33 in the modified example of the first embodiment.

[0106] A modified example of the first embodiment will be described below, but in the following description, differences from the first embodiment will be mainly described, and descriptions of similar matters will be omitted. Note that in FIG. 10, the same reference numerals are used for configurations similar to those of the first embodiment.

[0107] The modified example of the first embodiment is similar to the first embodiment except that a corner cube mirror 331 is provided instead of the corner cube prism 330 described above.

[0108] 10 has a corner cube mirror 331. The corner cube mirror 331 is also called a hollow retroreflector, and has the same retroreflectivity as the corner cube prism 330.

[0109] The corner cube mirror 331 shown in Figure 10 also has a retroreflective surface 334. The retroreflective surface 334 includes three faces. These three faces form the corners of a cube, and cause three mirror reflections. This allows light that is incident on the retroreflective surface 334 to return in the same direction as it was incident.

[0110] In addition, because the corner cube mirror 331 does not have an incident surface, losses at the time of incidence and exit can be suppressed. Furthermore, because light is specularly reflected on the retroreflective surface 334 of the corner cube mirror 331, there is no polarization dependency of the reflectance, and losses due to the polarization dependency of the reflectance can be suppressed. Therefore, by using the corner cube mirror 331, it is possible to further suppress the decrease in the S / N ratio of the interference signal.

[0111] The corner cube mirror 331 may be of any type, such as a mount type in which three mirrors are fixed to a mount member, or a replica type in which a film of a mirror material such as a metal is formed on a replica member having three mutually perpendicular surfaces. In the above modified example as well, the same effects as in the first embodiment can be obtained.

[0112] 3. Second embodiment Next, an interferometer according to a second embodiment will be described.

[0113] FIG. 11 is a side view showing corner cube prisms 330A and 330B provided as the movable mirror 33 in the second embodiment.

[0114] The second embodiment will be described below, focusing on the differences from the first embodiment and omitting the description of the similarities. Note that in FIG. 11, the same reference numerals are used to denote the same elements as in the first embodiment.

[0115] The second embodiment is similar to the first embodiment except that the configuration of the movable mirror 33 shown in FIG. 11 is different.

[0116] 11 has two corner cube prisms 330A and 330B. The corner cube prisms 330A and 330B are optical elements similar to the above-mentioned corner cube prism 330, and each has an entrance surface 332 and a retroreflective surface 334.

[0117] The two corner cube prisms 330A and 330B are disposed along the movement axis of the moving mirror 33.

[0118] The retroreflection surface 334 of the corner cube prism 330A is also referred to as the "analysis light reflection surface 334A." The analysis light reflection surface 334A reflects only the analysis light L1a, unlike the retroreflection surface 334 in the first embodiment described above. The retroreflection surface 334 of the corner cube prism 330B is also referred to as the "laser light reflection surface 334B." The laser light reflection surface 334B reflects only the measurement light L2b. For this reason, in the movable mirror 33 shown in FIG. 11, the optical path of the analysis light L1a and the optical path of the measurement light L2b are separated, and unintended mixing of the analysis light L1a and the measurement light L2b can be prevented. In addition, since the optical path adjustment to prevent mixing of the analysis light L1a and the measurement light L2b is not required, the difficulty of assembling the analysis optical system 3 can be reduced.

[0119] 11, the analytical light reflecting surface 334A and the laser light reflecting surface 334B are arranged to face in opposite directions, and are placed on the placement portion 338. This allows the measurement light L2b to be incident on the movable mirror 33 without any optical element for diverting the measurement light L2b, specifically, without the optical path changing mirrors 441 to 444 of the first embodiment. As a result, the configuration of the spectroscopic device 100 can be simplified.

[0120] 11 includes a member that integrates the corner cube prisms 330A and 330B. This allows the corner cube prisms 330A and 330B to be driven as a unit. As a result, the movement of the corner cube prism 330A can be detected with high accuracy by the reflection of the measurement light L2b on the corner cube prism 330B, further improving the accuracy of the final analysis result. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0121] In this embodiment, the laser light reflecting surface 334B has retroreflectivity, but the laser light reflecting surface 334B does not necessarily have to have retroreflectivity. In that case, the analytical optical system 3 can still enjoy the above-mentioned effects. Meanwhile, by making the laser light reflecting surface 334B retroreflective as in this embodiment, it is possible to suppress a decrease in the S / N ratio of the interference signal of the length measurement light L2a, L2b that is caused by shaking during movement of the movable mirror 33. This allows the position of the movable mirror 33 to be detected with greater accuracy.

[0122] 4. Modification of the Second Embodiment Next, a modification of the second embodiment will be described.

[0123] FIG. 12 is a side view showing corner cube mirrors 331A and 331B that the modified example of the second embodiment includes as movable mirror 33. As shown in FIG.

[0124] A modified example of the second embodiment will be described below, but in the following description, differences from the second embodiment will be mainly described, and descriptions of similar matters will be omitted. Note that in FIG. 12, the same reference numerals are used for configurations similar to those of the second embodiment.

[0125] The modified example of the second embodiment is similar to the second embodiment except that it has corner cube mirrors 331A and 331B instead of the above-mentioned corner cube prisms 330A and 330B.

[0126] 12 has corner cube mirrors 331A and 331B. Each of these mirrors also has a retroreflective surface 334. Light incident on each retroreflective surface 334 can return in the same direction as the incident direction.

[0127] The corner cube mirrors 331A and 331B do not have an incident surface, so that loss at the time of incidence and emission can be suppressed. Furthermore, since the light is specularly reflected on each retroreflective surface 334, there is no polarization dependency of the reflectance, so that loss due to the polarization dependency of the reflectance can be suppressed. Therefore, by using the corner cube mirrors 331A and 331B, unintended interference between the analytical light L1a and the length measurement light L2b can be further suppressed.

[0128] Each of the corner cube mirrors 331A and 331B may be of any type, such as a mount type or a replica type. In the above modified example as well, the same effects as those of the second embodiment can be obtained.

[0129] 5. Third embodiment Next, an interferometer according to a third embodiment will be described.

[0130] FIG. 13 is a schematic diagram showing a spectroscopic instrument 100 as an interferometer according to the third embodiment.

[0131] The third embodiment will be described below, focusing on the differences from the first embodiment and omitting the description of the similarities. In FIG. 13, the same reference numerals are used for the same configurations as the first embodiment.

[0132] The third embodiment is similar to the first embodiment, except that the configurations of the periodic signal generating unit 6 and the driving unit 8 are different. Specifically, in the third embodiment, the periodic signal generating unit 6 outputs not only the reference signal Ss but also a mirror driving signal Sm (reflection unit driving signal) for driving the motor M of the driving unit 8. This eliminates the need for a periodic signal generating unit required to generate the mirror driving signal Sm. In other words, the vibration element 30 is used not only as a signal source for the reference signal Ss but also as a signal source for the mirror driving signal Sm. As a result, the configuration can be simplified, and the spectroscopic device 100 can be made smaller, lighter, more power-efficient, and less expensive.

[0133] 13 includes an oscillation circuit 62 and a square wave generation circuit 64. The square wave generation circuit 64 converts the reference signal Ss, which is an analog signal output from the oscillation circuit 62, into a pulse signal Sp, which is a digital signal. An example of the square wave generation circuit 64 is an analog / digital conversion circuit using a comparator.

[0134] 13 includes a motor M, a power conversion unit 862, and a mirror drive signal generation unit 82. The mirror drive signal generation unit 82 generates a mirror drive signal Sm having a desired drive frequency based on the pulse signal Sp input from the periodic signal generation unit 6. Then, the mirror drive signal Sm is output to the stepping motor SPM to drive the moving mirror 33 via the power conversion unit 862. In the third embodiment as described above, the same effects as in the first embodiment can be obtained.

[0135] 6. Fourth embodiment Next, an interferometer according to a fourth embodiment will be described.

[0136] Fig. 14 is a schematic configuration diagram showing a shape measuring instrument 200 as an interferometer according to the fourth embodiment. Fig. 15 is a schematic configuration diagram showing main parts of the analysis unit 300, length measurement unit 400, periodic signal generation unit 6 and calculation unit 7 of Fig. 14.

[0137] The fourth embodiment will be described below, focusing on the differences from the first embodiment and omitting the description of the similarities. Note that in Fig. 14 and Fig. 15, the same reference numerals are used to denote the same items as in the first embodiment.

[0138] The spectrometer 100 of the first embodiment is an apparatus that irradiates a sample 9 with analytical light L1 emitted from a first light source 51 and performs spectroscopic analysis of the sample 9. In contrast, the shape measuring apparatus 200 of the fourth embodiment is an apparatus that irradiates a sample 9 with analytical light L1 and performs shape measurement of the surface and inside of the sample 9. The shape measuring apparatus 200 shown in FIG. 14 is similar to the spectrometer 100 shown in FIG. 1 except that the configuration of the analytical optical system 3 is different.

[0139] The analytical optical system 3 shown in FIG. 14 includes a first light source 51, a beam splitter 32, a movable mirror 33, a condenser lens 35, a condenser lens 37, and a first light receiving element .

[0140] 14 may be, for example, a white light source such as an SLD (Super Luminescent Diode) or an LED (Light Emitting Diode), a wavelength swept light source, or the various lamps listed in the first embodiment. Preferably, a broadband light source called a low coherence light source is used.

[0141] The analytical light L1 emitted from the first light source 51 is split into two by the beam splitter 32. The beam splitter 32 shown in Fig. 14 reflects a part of the analytical light L1 as analytical light L1a toward the movable mirror 33, and transmits the other part of the analytical light L1 toward the sample 9 as analytical light L1b. The analytical light L1b is collected by the collecting lens 37 and irradiated onto the sample 9.

[0142] Moreover, the beam splitter 32 transmits the analytical light L1a reflected by the movable mirror 33 toward the first light receiving element 36, and reflects the analytical light L1b reflected by the sample 9 toward the first light receiving element 36. Therefore, the beam splitter 32 mixes the split analytical light L1a, L1b to generate interference light.

[0143] The first light receiving element 36 receives the interference light and acquires its intensity. Then, a signal indicating the change in intensity over time is output as a first light receiving signal F(t). This first light receiving signal F(t) includes a sample-derived component generated by the interaction between the analytical light L1b and the sample 9, and phase information derived from the movable mirror 33 described above. The sample-derived component is, for example, a change in phase added to the analytical light L1b according to the surface shape of the sample 9.

[0144] Examples of the first light receiving element 36 include a photodiode, a phototransistor, and an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). By using an image sensor, a two-dimensional distribution of the first light receiving signal F(t) can be acquired. This allows the surface shape of the sample 9 to be measured two-dimensionally.

[0145] The length measurement optical system 4, periodic signal generating section 6 and driving section 8 shown in FIG. 14 are the same as those in FIG. The calculation unit 7 shown in FIG. 15 has a moving mirror position calculation unit 72, a light intensity calculation unit 74, and a shape calculation unit 78.

[0146] Similar to the first embodiment, a light intensity calculation section 74 shown in Fig. 15 generates a waveform (interferogram F(x)) representing the intensity of the first light receiving signal F(t) at each position of the movable mirror 33 based on the first light receiving signal F(t) and the movable mirror position signal X(t). A shape calculation section 78 shown in Fig. 15 calculates the surface shape of the sample 9 based on this waveform. Specific analysis methods are known as white light interferometry, time domain OCT (Optical Coherence Tomography), etc.

[0147] 14 illustrates a case where the sample 9 reflects the analytical light L1b, but when the sample 9 transmits the analytical light L1b, the shape measuring device 200 illustrated in Fig. 14 can measure the internal shape (internal structure) of the sample 9. A specific analysis method is known as optical coherence tomography, etc. In the fourth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0148] 7. Effects of the above embodiments The interferometer (spectrometer 100 or shape measuring device 200) according to each of the above-mentioned embodiments includes an analytical optical system 3, a length measuring optical system 4, and a driving unit 8. The analytical optical system 3 includes a movable mirror 33 (retroreflector) and a first light receiving element 36. The movable mirror 33 reflects the analytical light L1a. The first light receiving element 36 receives the analytical light L1a and L1b, and outputs a first light receiving signal. The analytical optical system 3 irradiates the sample 9 with the analytical light L1 and causes interference between the analytical light L1a and L1b. The length measuring optical system 4 includes a second light source 41 (laser light source), an optical modulator 12, and a second light receiving element 45. The second light source 41 emits length measuring light L2 (laser light). The optical modulator 12 modulates the frequency of the length measuring light L2a using the vibration element 30, and adds a modulated component. The second light receiving element 45 receives the measurement light L2a, L2b including a measurement component and a modulation component generated by irradiating the moving mirror 33 with the measurement light L2b, and outputs a second light receiving signal S2. The measurement optical system 4 causes interference between the measurement light L2a, L2b. The driving unit 8 changes the position of the moving mirror 33.

[0149] With this configuration, since the movable mirror 33 has retroreflectivity, it is possible to suppress a decrease in the S / N ratio of the interference signal of the analytical lights L1a, L1b that is caused by shaking when the movable mirror 33 moves (changes its position). Furthermore, since the movable mirror 33 has retroreflectivity, it is possible to increase the tolerance for shaking that occurs when the movable mirror 33 moves, so that it is easy to suppress a decrease in the S / N ratio of the interference signal even if the driving accuracy of the driver 8 is reduced. This makes it possible to suppress an increase in the size of the driver 8, and to achieve a smaller, lighter, and less costly interferometer.

[0150] In the interferometer (spectroscopic device 100 or shape measuring device 200) according to each of the above-described embodiments, the movable mirror 33 (retroreflector) has a retroreflecting surface 334 and a mounting portion 338. The retroreflecting surface 334 has retroreflectivity and reflects the analytical light L1a and the length measuring light L2b (laser light). The mounting portion 338 has the retroreflecting surface 334 mounted thereon and is driven by the driving portion 8.

[0151] According to such a configuration, it is possible to ensure a sufficiently long movement amount of the movable mirror 33, and it is possible to easily increase the wavelength resolution (wavenumber resolution) of the acquired spectrum pattern.

[0152] In the interferometer (spectrometer 100 or shape measuring instrument 200) according to each of the above-described embodiments, the position at which analytical light L1a is reflected on retroreflective surface 334 differs from the position at which measurement light L2b (laser light) is reflected.

[0153] According to this configuration, it is possible to suppress interference between the analytical light L1a and the measurement light L2b, and as a result, it is possible to suppress a decrease in the S / N ratio in the measurement components and the components derived from the sample.

[0154] In the interferometer (spectrometer 100 or shape measuring device 200) according to each of the above-described embodiments, the movable mirror 33 (retroreflecting section) has an analytical light reflecting surface 334A, a laser light reflecting surface 334B, and a mounting section 338. The analytical light reflecting surface 334A has retroreflectivity and reflects the analytical light L1a. The laser light reflecting surface 334B reflects the measurement light L2b (laser light). The mounting section 338 has the analytical light reflecting surface 334A and the laser light reflecting surface 334B mounted thereon, and is driven by the driving section 8.

[0155] With this configuration, the analytical light reflecting surface 334A reflects only the analytical light L1a, and the laser light reflecting surface 334B reflects only the measurement light L2b, so that the optical path of the analytical light L1a and the optical path of the measurement light L2b can be separated, and unintentional mixing of the analytical light L1a and the measurement light L2b can be prevented.

[0156] In the interferometer (spectrometer 100 or shape measuring instrument 200) according to each of the above-described embodiments, the laser light reflecting surface 334B has retroreflective properties.

[0157] According to such a configuration, it is possible to suppress a decrease in the S / N ratio of the interference signal of the length-measuring lights L2a and L2b, which is caused by shaking when the movable mirror 33 moves (changes its position).

[0158] In the interferometer (spectrometer 100 or shape measuring instrument 200) according to each of the above-described embodiments, the analytical light reflecting surface 334A and the laser light reflecting surface 334B face in opposite directions.

[0159] According to this configuration, even if there is no optical element for diverting the measurement light L2b, the measurement light L2b can be made to naturally enter the movable mirror 33. As a result, it becomes easier to simplify the configuration of the interferometer.

[0160] In the interferometer (spectrometer 100 or shape measuring device 200) according to each of the above-described embodiments, the driver 8 drives the movable mirror 33 (retroreflector) based on the mirror drive signal Sm (reflector drive signal). In this case, the vibration element 30 may be a signal source of the mirror drive signal Sm.

[0161] With such a configuration, the configuration of the interferometer can be simplified, and the interferometer can be made smaller, lighter, consume less power, and at lower costs.

[0162] In the interferometer (spectrometer 100 or shape measuring device 200) according to each of the above-described embodiments, the analytical optical system 3 has a beam splitter 32 (light splitting section), a movable mirror 33 (retroreflecting section), and a fixed mirror 34 (fixed reflecting section). The beam splitter 32 splits the analytical light L1 into two and mixes the split analytical light L1a and L1b. The movable mirror 33 reflects one of the split analytical light L1 (analytical light L1a) toward the beam splitter 32. The fixed mirror 34 reflects the other of the split analytical light L1 (analytical light L1b) toward the beam splitter 32. The fixed mirror 34 may have retroreflectivity.

[0163] According to such a configuration, it is possible to suppress a decrease in the S / N ratio of the interference signal caused by an angular deviation (deviation angle) in the arrangement of the fixed mirror .

[0164] In the interferometer (spectrometer 100 or shape measuring instrument 200) according to each of the above-described embodiments, the movable mirror 33 (retroreflecting portion) may have a corner cube prism 330.

[0165] According to such a configuration, it is possible to provide retroreflective properties to movable mirror 33 using a single component (corner cube prism 330), so that movable mirror 33 can be easily simplified, made smaller, lighter, and less expensive.

[0166] In the interferometer (spectrometer 100 or shape measuring device 200) according to each of the above embodiments, the movable mirror 33 (retroreflecting portion) may have an anti-reflection coating 333 provided on the entrance surface 332 of the corner cube prism 330.

[0167] According to such a configuration, it is possible to increase the incidence efficiency of the light (analysis light L1a and measurement light L2b) incident on the incident surface 332. It is also possible to increase the emission efficiency of the light (analysis light L1a and measurement light L2b) emitted from the incident surface 332. Furthermore, it is possible to suppress the generation of reflected stray light at the incident surface 332 and to suppress the generation of noise caused by the reflected stray light being incident on the first light receiving element 36. As a result, it is possible to suppress a decrease in the S / N ratio of the measurement components and the sample-derived components.

[0168] In the interferometer (spectrometer 100 or shape measuring instrument 200) according to each of the above-described embodiments, the movable mirror 33 (retroreflecting portion) may have a corner cube mirror 331.

[0169] With this configuration, since the corner cube mirror 331 does not have an entrance surface, it is possible to suppress losses at the time of incidence and exit. Also, since light is specularly reflected on the retroreflective surface 334 of the corner cube mirror 331, there is no polarization dependency of the reflectance, and it is possible to suppress losses due to the polarization dependency of the reflectance.

[0170] While the interferometer of the present invention has been described above based on the illustrated embodiments, the interferometer of the present invention is 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.

[0171] The interferometer of the present invention may be a combination of two or more of the above-described embodiments and their modifications. Furthermore, each functional unit of the interferometer of the present invention may be divided into multiple elements, or multiple functional units may be integrated into one.

[0172] 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.

[0173] Furthermore, the arrangement of the sample is not limited to the arrangement shown in the figure. Since the sample-derived components are generated by applying analytical light to the sample, the sample can be arranged at any position as long as the analytical light emitted from the sample can be incident on the first light receiving element. [Explanation of symbols]

[0174] 3...Analysis optical system, 4...Length measurement optical system, 6...Periodic signal generating section, 7...Calculation section, 8...Drive section, 9...Sample, 12...Optical modulator, 30...Vibration element, 32...Beam splitter, 33...Moving mirror, 34...Fixed mirror, 35...Condensing lens, 36...First light receiving element, 37...Condensing lens, 41...Second light source, 42...Beam splitter, 45...Second light receiving element, 46...1 / 2 wave plate, 47...1 / 2 wave plate, 48...1 / 4 wave plate, 49...Analyzer, 51...First light source, 54...Beam splitter, 55...Condensing lens, 56...Natural attenuation filter, 62...Oscillation circuit, 64...Square wave generating circuit, 72 ...moving mirror position calculation unit, 74...light intensity calculation unit, 76...Fourier transform unit, 78...shape calculation unit, 82...mirror drive signal generation unit, 100...spectroscopic device, 200...shape measurement device, 300...analysis unit, 330...corner cube prism, 330A...corner cube prism, 330B...corner cube prism, 331...corner cube mirror, 331A...corner cube mirror, 331B...corner cube mirror, 332...incident surface, 333...anti-reflection coating, 334...retroreflective surface, 334A...analysis light reflecting surface, 334B...laser light reflecting surface, 335...surface, 35a...region, 335b...region, 336...surface, 336a...region, 336b...region, 337...surface, 337a...region, 337b...region, 338...mounting portion, 341...flat mirror, 342...flat mirror, 400...length measuring portion, 401...base, 402...first vibrating arm, 403...second vibrating arm, 404...electrode, 405...electrode, 406...light reflecting surface, 431...vibrating piece, 432...groove, 433...pad, 434...diffraction grating, 435...pad, 436...vibration direction, 441...optical path changing mirror, 442...optical path changing mirror, 443...optical path changing mirror, 444...optical path changing mirror, 445...beam Splitter, 722...pre-processing section, 724...demodulation processing section, 726...moving mirror position signal output section, 862...power conversion section, 4311...front surface, 4312...rear surface, F(x)...interferogram, F(t)...first light receiving signal, L1...analysis light, L1a...analysis light, L1b...analysis light, L2...length measuring light, L2a...length measuring light, L2b...length measuring light, LP1...light path, LP2...light path, M...motor, S2...second light receiving signal, SP0...spectrum pattern, Sd...element drive signal, Sm...mirror drive signal, Sp...pulse signal, Ss...reference signal, X(t)...moving mirror position signal, X9...absorption peak

Claims

1. an analytical optical system having a retroreflection unit that reflects the analytical light and a first light receiving element that receives the analytical light and outputs a first light receiving signal, the analytical optical system irradiating the sample with the analytical light and causing interference with the analytical light; A length measurement optical system that includes a laser light source that emits laser light, an optical modulator that modulates the frequency of the laser light using a vibration element and adds a modulated component, and a second light receiving element that receives the laser light including a length measurement component and the modulated component generated by irradiating the laser light to the retroreflection portion and outputs a second light receiving signal, and performs interference of the laser light; A drive unit that changes the position of the retroreflective unit; An interferometer comprising:

2. The retroreflective portion is A retroreflective surface having retroreflective properties and reflecting the analytical light and the laser light; A mounting section on which the retroreflective surface is mounted and which is driven by the driving section; 2. The interferometer of claim 1, comprising:

3. 3. The interferometer according to claim 2, wherein a position at which the analytical light is reflected and a position at which the laser light is reflected are different on the retroreflective surface.

4. The retroreflective portion is an analytical light reflecting surface having retroreflectivity and reflecting the analytical light; a laser light reflecting surface that reflects the laser light; a mounting section on which the analytical light reflecting surface and the laser light reflecting surface are mounted and which is driven by the driving section; 2. The interferometer of claim 1, comprising:

5. 5. The interferometer of claim 4, wherein the laser light reflecting surface is retroreflective.

6. 6. An interferometer according to claim 4, wherein the analytical light reflecting surface and the laser light reflecting surface face in opposite directions.

7. The drive unit drives the retroreflection unit based on a reflection unit drive signal, The interferometer according to claim 1 , wherein the vibration element is a signal source of the reflector drive signal.

8. The analysis optical system includes: a light splitting unit that splits the analytical light into two and mixes the split analytical light; The retroreflection unit reflects one of the split analytical lights toward the light splitting unit; a fixed reflecting section that reflects the other of the split analytical lights toward the light splitting section; having The interferometer according to claim 1 , wherein the fixed reflecting portion is retroreflective.

9. The interferometer of claim 1 , wherein the retroreflecting portion comprises a corner cube prism.

10. The interferometer according to claim 9 , wherein the retroreflecting portion has an antireflection coating provided on an entrance surface of the corner cube prism.

11. The interferometer according to claim 1 , wherein the retroreflecting portion comprises a corner cube mirror.

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