Laser interferometer

Abstract

To realize a laser interferometer easy to downsize, difficult to lower a measuring precision even with disturbances applied, and excellent in usability.SOLUTION: A laser interferometer includes: a laser light source configured to emit laser light; a light splitter configured to split the laser light into first split light and second split light; an optical modulator configured to modulate a frequency of the first split light to generate reference-light; a photodetector configured to receive the reference-light and object-light generated through reflecting the second split light by an object; and a light diameter expander configured to expand a light diameter of incoming light. An optical path of the reference light includes a first non-coaxial part shifting from an optical path of the first split light or an optical path of the object light includes a second non-coaxial part shifting from an optical path of the second split light. The light diameter expander is arranged on the first non-coaxial part or the second non-coaxial part.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a laser interferometer.

Background Art

[0002] Patent Document 1 discloses a laser vibrometer as a device for measuring the vibration speed of an object. In this laser vibrometer, a laser beam is irradiated onto the object to be measured, and the vibration speed is measured based on the scattered laser beam that has received the Doppler shift.

[0003] The laser vibrometer described in Patent Document 1 includes a vibration element that generates a predetermined frequency. This vibration element shifts the frequency of the incident laser beam based on its vibration frequency and generates a reflected laser beam having a frequency different from that of the incident laser beam. In the laser vibrometer, this reflected laser beam is used as a reference light. Then, the light obtained by combining the scattered laser beam derived from the object to be measured and the reference light is received by a photodetector, and a beat signal is electrically extracted. Then, the vibration speed of the object to be measured is measured from this beat signal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a laser interferometer such as a laser vibrometer, the scattered laser beam (object light) derived from the object to be measured and the reference light are combined and received by a photodetector. At this time, interference occurs in the region where the beam of the object light and the beam of the reference light overlap (overlap region), and it becomes possible to measure the vibration speed of the object and the like.

[0006] However, when forming the overlapping region as described above, it takes time to align (align) each part constituting the interference optical system. This leads to a decrease in the usability of the laser interferometer. Further, when the alignment is disrupted due to external disturbances such as vibration or impact, the measurement accuracy decreases. On the other hand, it is also conceivable to cancel the influence of external disturbances using a sensor or the like. In that case, there is a concern about an increase in the size and weight of the device.

[0007] Therefore, it has become an issue to realize a laser interferometer that is suppressed in size, is less likely to have its measurement accuracy decreased even when external disturbances are applied, and is excellent in usability.

Means for Solving the Problem

[0008] The laser interferometer according to the application example of the present invention a laser light source that emits laser light, an optical splitter that splits the laser light into a first split light and a second split light, an optical modulator that modulates the frequency of the first split light to generate reference light, a light receiving element that receives object light generated by reflecting the second split light from an object and the reference light, an optical path expander that expands the optical path of the incident light, is provided with the optical path of the reference light is configured to include a first non-coaxial portion that is displaced from the optical path of the first split light, or the optical path of the object light is configured to include a second non-coaxial portion that is displaced from the optical path of the second split light, the optical path expander is disposed in the first non-coaxial portion or the second non-coaxial portion.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the laser interferometer of the present invention will be described in detail based on the embodiments shown in the accompanying drawings. 1. First Embodiment FIG. 1 is a functional block diagram showing a laser interferometer 1 according to the first embodiment. FIG. 2 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 of FIG. 1.

[0011] In the laser interferometer 1 shown in FIG. 1, the object 14 and the optical modulator 12 shown in FIG. 2 are irradiated with laser light (first split light L1a and second split light L1b). Then, the object light L3 emitted from the object 14 and the reference light L2 emitted from the optical modulator 12 are interfered, and the interference light is received by the light receiving element 10 to obtain a light receiving signal. Then, by the optical heterodyne interference method, a sample signal derived from the object 14 is extracted from the light receiving signal, and based on the sample signal, the displacement and speed of the object 14 are measured.

[0012] The laser interferometer 1 shown in FIG. 1 includes a sensor head unit 51 and a main body unit 59. The sensor head unit 51 shown in Fig. 1 includes an interference optical system 50 and a signal generation unit 60. Since the sensor head unit 51 is easy to miniaturize and lightweight, and is easy to make portable and easy to install, for example, it can be easily arranged near the object 14.

[0013] The main body unit 59 includes a demodulation calculation unit 52. The demodulation calculation unit 52 demodulates the sample signal derived from the object 14 from the received light signal. The main body unit 59 shown in Fig. 1 is separated from the sensor head unit 51, but may be integrated with the sensor head unit 51. Also, at least one of the elements included in the sensor head unit 51 shown in Fig. 1 may be included in the main body unit 59.

[0014] 1.1. Interference optical system The interference optical system 50 shown in Fig. 2 is a Michelson type interference optical system. The interference optical system 50 includes a laser light source 2, an optical splitter 4, a light receiving element 10, an optical modulator 12, and an optical path expander 13.

[0015] The laser light source 2 emits an emitted light L1 which is laser light. The emitted light L1 passes through the optical path P1 and enters the optical splitter 4. The optical path refers to the path along which light travels. The optical splitter 4 splits the emitted light L1 into a first split light L1a and a second split light L1b.

[0016] The first split light L1a passes through the optical path P1a and enters the optical modulator 12. The optical modulator 12 includes a vibration element 30, modulates the frequency of the first split light L1a, and generates a reference light L2 which is laser light including a modulation signal. The modulation signal is a change in frequency added to the first split light L1a by the optical modulator 12. The reference light L2 passes through the optical path P2 and enters the optical splitter 4.

[0017] The second split light L1b passes through the optical path P1b and is incident on the object 14. The second split light L1b incident on the object 14 is reflected as object light L3, which is laser light containing a sample signal derived from the object 14. The sample signal is a Doppler signal associated with the displacement of the object 14 and is a change in the frequency added to the second split light L1b. The object light L3 passes through the optical path P3 and is incident on the optical splitter 4.

[0018] The optical splitter 4 mixes the reference light L2 and the object light L3. The mixed reference light L2 passes through the optical path P4 and is incident on the light receiving element 10, and the mixed object light L3 passes through the optical path P4 and is incident on the light receiving element 10. The optical paths P2 and P3 overlap each other in space, and light interference occurs at this overlapping portion. The light receiving element 10 detects the intensity of the light in which the reference light L2 and the object light L3 are mixed and outputs a light receiving signal corresponding to the intensity.

[0019] In the interference optical system 50 as described above, the phase information of the object 14 is obtained by the optical heterodyne interference method. Specifically, two lights (reference light L2 and object light L3) with slightly different frequencies are made to interfere, and the phase information is extracted from the obtained interference light. Then, the displacement of the object 14 is obtained from the phase information in the demodulation arithmetic unit 52 described later. In the optical heterodyne interference method, when extracting the phase information from the interference light, it is less affected by stray light and the like that become noise.

[0020] 1.1.1. Laser light source The laser light source 2 is a laser light source that emits injection light L1 having coherence. As the laser light source 2, a light source with a line width of MHz band or less is preferably used. Specifically, gas lasers such as He-Ne lasers, DFB-LD (Distributed FeedBack - Laser Diode), FBG-LD (Fiber Bragg Grating Laser Diode), VCSEL (Vertical Cavity Surface Emitting Laser Diode), and semiconductor laser elements such as FP-LD (Fabry-Perot Laser Diode) can be mentioned.

[0021] The laser light source 2 is particularly preferably a semiconductor laser element. Thereby, it becomes possible to particularly miniaturize the laser light source 2. For this reason, the laser interferometer 1 can be miniaturized.

[0022] Note that a collimating lens for collimating the injection light L1 may be provided at the subsequent stage of the laser light source 2.

[0023] 1.1.2. Optical splitter The optical splitter 4 shown in Fig. 2 is an unpolarized beam splitter or a non-polarized beam splitter that splits the injection light L1 at a predetermined ratio. As an example, the optical splitter 4 shown in Fig. 2 reflects a part of the injection light L1 to generate a first split light L1a, and transmits the other part of the injection light L1 to generate a second split light L1b. Since an unpolarized beam splitter or a non-polarized beam splitter does not require a wavelength plate or the like for controlling polarization, it contributes to reducing the number of optical elements constituting the interference optical system 50.

[0024] In addition, the optical splitter 4 has a function of mixing the incident reference light L2 and object light L3. When the reference light L2 is incident on the optical splitter 4 shown in FIG. 2, a part of the light quantity is transmitted. When the object light L3 is incident on the optical splitter 4 shown in FIG. 2, a part of the light quantity is reflected. A part of the reference light L2 and a part of the object light L3 are mixed and incident on the light receiving element 10 as mixed light.

[0025] In FIG. 2, the reference light L2 is incident on the optical splitter 4 after passing through the optical path expander 13, but the incident position at this time is different from the emission position of the first split light L1a. That is, in FIG. 2, by adjusting the postures of the optical modulator 12 and the light receiving element 10, the optical path P1a of the first split light L1a and the optical path P2 of the reference light L2 are displaced (non-coaxial). As a result, the optical path P2 includes a portion (first non-coaxial portion NC1) displaced from the optical path P1a. The optical path expander 13 is disposed in the first non-coaxial portion NC1. Then, the first split light L1a is not incident on the optical path expander 13, and only the reference light L2 is incident. According to such a configuration, the first non-coaxial portion NC1 can be formed only by adjusting the postures of the optical modulator 12 and the light receiving element 10 to displace the optical path P2 from the optical path P1a. That is, an interference optical system 50 in which the optical path expander 13 can be arranged can be constructed without increasing the number of components.

[0026] In FIG. 2, the object light L3 is also incident on the optical splitter 4, but the incident position at this time is also different from the emission position of the second split light L1b. That is, in FIG. 2, by adjusting the postures of the object 14 and the light receiving element 10, the optical path P1b of the second split light L1b and the optical path P3 of the object light L3 are displaced (non-coaxial). As a result, the optical path P3 includes a portion (second non-coaxial portion NC2) displaced from the optical path P1b. According to such a configuration, the second non-coaxial portion NC2 can be formed only by displacing the optical path P3 from the optical path P1b. In the same optical path P4 formed at the subsequent stage of the optical splitter 4, the reference light L2 and the object light L3 can be mixed with each other.

[0027] As the types of the optical splitter 4, for example, in addition to the plate type element shown in FIG. 2, a cube type element, a stacked type element, etc. can be mentioned. Among these, from the viewpoint that the influence of the return light due to the interface reflection (reflection when entering from air into the glass material) is small, in the case of this embodiment, the plate type element is preferably used.

[0028] 1.1.3. Light receiving element The light receiving element 10 outputs a photocurrent (light receiving signal) corresponding to the intensity of the mixed light. Examples of the light receiving element 10 include a photodiode, a phototransistor, etc. Note that what the light receiving element 10 receives only needs to be light including the sample signal and the modulation signal, and is not limited to the interference light of the reference light L2 including the modulation signal as described above and the object light L3 including the sample signal. Also, “demodulating the sample signal from the light receiving signal” in this specification includes demodulating the sample signal from various signals converted from the photocurrent (light receiving signal).

[0029] 1.1.4. Optical modulator Next, the optical modulator 12 including the vibrating element 30 will be described.

[0030] The optical modulator 12 shown in FIG. 2 has a vibrating element 30. The vibrating element 30 vibrates in thickness shear at a predetermined mechanical resonance frequency and has a diffraction grating (not shown). When the first split light L1a is irradiated onto this diffraction grating, diffracted light with a shifted frequency is generated, and the reference light L2 including the modulation signal is obtained.

[0031] Examples of the vibrating element 30 include a crystal oscillator, a silicon oscillator, a ceramic oscillator, a piezo element, etc. Among these, the vibrating element 30 is preferably a crystal oscillator, a silicon oscillator, or a ceramic oscillator. These oscillators are different from other oscillators, for example, piezo elements, etc., because they are oscillators that utilize the mechanical resonance phenomenon, so the Q value is high and the stabilization of the natural vibration frequency can be easily achieved.

[0032] Further, according to the optical modulator 12 having the vibration element 30, the volume and weight can be significantly reduced compared to, for example, an optical modulator having an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). Therefore, the laser interferometer 1 can be miniaturized, lightened, and its power consumption can be reduced. Note that if these effects are not required, the optical modulator 12 may be replaced with an optical modulator using an AOM or an EOM.

[0033] Examples of the optical modulator 12 include the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156. This publication mentions a quartz AT oscillator as the vibration element 30. Further, as the vibration element 30, an SC-cut quartz oscillator, a tuning fork type quartz oscillator, a surface acoustic wave element made of quartz, or the like may be used.

[0034] A silicon oscillator is an oscillator including a single crystal silicon piece manufactured from a single crystal silicon substrate using MEMS technology and a piezoelectric film. MEMS (Micro Electro Mechanical Systems) refers to a micro electro mechanical system. Examples of the shape of the single crystal silicon piece include a cantilever shape such as a two-pronged tuning fork type or a three-pronged tuning fork type, and a double-cantilever shape. The oscillation frequency of the silicon oscillator is, for example, about 1 kHz to several hundred MHz.

[0035] A ceramic oscillator is an oscillator including a piezoelectric ceramic piece manufactured by sintering piezoelectric ceramics and an electrode. Examples of the piezoelectric ceramics include lead zirconate titanate (PZT), barium titanate (BTO), and the like. The oscillation frequency of the ceramic oscillator is, for example, about several hundred kHz to several tens of MHz.

[0036] Among these, a quartz oscillator is preferably used as the vibration element 30. Since quartz itself is a piezoelectric material, the quartz oscillator has particularly high frequency stability.

[0037] 1.1.5. Optical Path Expander The optical path expander 13 shown in Fig. 2 is disposed in the first non-coaxial portion NC1. This optical path expander 13 has a function of expanding the optical path of the incident reference light L2. Thereby, the reference light L2 with an expanded optical path is obtained.

[0038] Any optical component having the above function can be used for the optical path expander 13. For example, an optical component called a beam expander is used. Examples of the beam expander include a Keplerian beam expander, a Galilean beam expander, and the like. Fig. 2 illustrates, as an example, the optical elements included in a Keplerian beam expander. The optical path expander 13 shown in Fig. 2 has a first lens 131 and a second lens 132. The optical path of the reference light L2 incident on the optical path expander 13 is expanded to a predetermined magnification by the first lens 131 and the second lens 132. The magnification of the optical path in the optical path expander 13 is not particularly limited and is appropriately set according to the effective diameter of the light receiving element 10, the optical path of the object light L3, the magnitude of the disturbance that disturbs the optical axes of the reference light L2 and the object light L3, and the like.

[0039] By expanding the optical path of the reference light L2 in this way, the reference light L2 and the object light L3 pass through the same space in the optical path P4, and the probability of interference with each other can be increased. Thereby, the light receiving element 10 can more surely receive the mixed light including the interference signal (beat signal) generated by the interference.

[0040] Fig. 3 is a conceptual diagram for explaining the operation and effect of the optical path expander 13 shown in Fig. 2. Fig. 3 shows images of the light intensity distributions when the optical path displacements of the optical paths P2 and P3 due to the disturbance occur in the case where there is no optical path expander 13 and in the case where there is an optical path expander 13. In this image, the horizontal axis indicates the optical paths and positions of the reference light L2 and the object light L3, and the vertical axis indicates the light intensity. Therefore, each curve in Fig. 3 shows the light intensity distribution of the reference light L2 and the object light L3.

[0041] When a displacement occurs in the optical paths P2 and P3, the position reaching the light receiving element 10 also shifts. Then, the region where the reference light L2 and the object light L3 overlap and interfere (interference region IF) becomes smaller according to the displacement amount. The size of the interference region IF and the light intensity in the interference region IF are reflected in the S / N ratio (signal-to-noise ratio) of the received signal.

[0042] When there is no optical path expander 13, the optical path of the reference light L2 and the optical path of the object light L3 at the light receiving element 10 are about the same. In this case, even a slight displacement is strongly reflected by the S / N ratio (signal-to-noise ratio) of the received signal. Specifically, since each optical path is about the same, the interference region IF becomes smaller according to the displacement amount. As a result, the interference signal becomes smaller and the S / N ratio of the received signal decreases. Also, the light intensity distributions of the reference light L2 and the object light L3 have a Gaussian distribution shape as shown in, for example, FIG. 3. When the optical path is small, the slope of the light intensity distribution also becomes steep. Then, the influence of the displacement is more strongly reflected in the interference signal, easily leading to a decrease in the S / N ratio of the received signal. Therefore, when there is no optical path expander 13, the displacement of the optical paths P2 and P3 easily leads to a decrease in the S / N ratio of the received signal. For these reasons, the disturbance resistance is lowered and the difficulty of alignment of the interference optical system 50 also increases.

[0043] On the other hand, when the optical path expander 13 is arranged in the first non-coaxial portion NC1, the optical path of the reference light L2 can be expanded more than the optical path of the object light L3. In this case, even if there is a slight displacement, a sufficient interference region IF can be ensured. As a result, even if there is a displacement, a decrease in the S / N ratio of the received signal can be suppressed. Also, when the optical path is expanded, the slope of the light intensity distribution of the reference light L2 becomes relatively gentle as shown in FIG. 3 compared to the case where the optical path expander 13 is not arranged. In this case, the influence of the displacement is less likely to be reflected in the S / N ratio of the received signal. Therefore, by providing the optical path expander 13, the disturbance resistance (robustness) of the measurement accuracy can be enhanced. That is, a laser interferometer 1 can be realized in which the measurement accuracy is less likely to decrease even when a disturbance is applied.

[0044] In addition, since the width of the light intensity distribution of the reference light L2 expands as the optical path length is extended, interference is likely to occur even if there is a misalignment in the optical paths P2 and P3. Therefore, when aligning the interference optical system 50 before or during measurement, it becomes easier to acquire an interference signal, and the work can be carried out based on the intensity of the interference signal. Thus, a laser interferometer 1 can be realized in which the alignment of the interference optical system 50 is easy and the usability is excellent.

[0045] In the laser interferometer 1 shown in FIG. 2, the above-described effects are realized by the arrangement of the optical path expander 13. Since the optical path expander 13 is sufficiently small and lightweight, it can contribute to the miniaturization of the laser interferometer 1. Further, since the laser interferometer 1 does not require a feedback mechanism for detecting disturbances and reflecting them in the measurement, it is also easy to reduce the size and weight from this perspective.

[0046] In FIG. 2, the optical path expander 13 is arranged only in the first non-coaxial portion NC1, but another optical path expander may be arranged in the second non-coaxial portion NC2. In this case, the two optical path expanders may have different magnification factors for expanding the optical path length.

[0047] 1.2. Signal generation unit The signal generation unit 60 shown in FIG. 1 outputs a drive signal input to the vibration element 30 and a reference signal input to the demodulation arithmetic unit 52.

[0048] The signal generation unit 60 shown in FIG. 1 includes an oscillation circuit 61. The oscillation circuit 61 drives the vibration element 30 at a predetermined frequency (outputs a drive signal to the vibration element 30) and outputs a reference signal. The vibration element 30 is driven by the drive signal and adds a modulation signal to the first split light L1a. Then, in the demodulation arithmetic unit 52, the received light signal including this modulation signal is demodulated based on the reference signal. Therefore, even if disturbances are added to the modulation signal and the reference signal respectively, the influence of the disturbance can be canceled or reduced in the demodulation arithmetic unit 52. Thereby, a laser interferometer 1 capable of more accurate measurement can be realized.

[0049] As the oscillation circuit 61, for example, an oscillation circuit disclosed in Japanese Patent Laid-Open No. 2022-38156 can be mentioned, but an oscillation circuit having other configurations may also be used.

[0050] Further, instead of the oscillation circuit 61, the signal generation unit 60 may be provided with a signal generator such as a function generator or a signal generator.

[0051] 1.3. Demodulation calculation unit The demodulation calculation unit 52 shown in FIG. 1 includes a preprocessing unit 53, a demodulation processing unit 54, and a demodulated signal output unit 55. The functions exhibited by these functional units are realized by hardware including, for example, a processor, a memory, an external interface, an input unit, a display unit, etc. Specifically, it is realized by the processor reading and executing a program stored in the memory. Note that these components can communicate with each other via an external bus.

[0052] Examples of the processor include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. Instead of the method in which these processors execute software, a method in which an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc. realize the above-described functions may be adopted.

[0053] Examples of the memory include an HDD (Hard Disk Drive), an SSD (Solid State Drive), an EEPROM (Electrically Erasable Programmable Read-Only Memory), a ROM (Read-Only Memory), a RAM (Random Access Memory), etc.

[0054] Examples of external interfaces include digital input / output ports such as USB (Universal Serial Bus), Ethernet (registered trademark) ports, wireless LAN (Local Area Network), Bluetooth (registered trademark), and the like.

[0055] Examples of the input unit include various input devices such as keyboards, mice, touch panels, and touch pads. Examples of the display unit include liquid crystal display panels, organic EL (Electro Luminescence) display panels, and the like.

[0056] Note that the external interface, the input unit, and the display unit may be provided as necessary and may be omitted.

[0057] For example, the preprocessing unit 53 and the demodulation processing unit 54 can apply the preprocessing unit and the demodulation unit disclosed in Japanese Patent Application Laid-Open No. 2022-38156.

[0058] The preprocessing unit 53 performs preprocessing on the received signal based on a reference signal. The preprocessing refers to a process of performing an operation on the received signal based on the reference signal to generate a signal (preprocessed signal) to which a known quadrature detection method can be applied.

[0059] The demodulation processing unit 54 demodulates a sample signal derived from the object 14 based on a reference signal from the preprocessed signal output from the preprocessing unit 53, for example, by a quadrature detection method.

[0060] The demodulated signal output unit 55 performs phase connection such as an unwrapping process on the sample signal, specifically, the phase information derived from the object 14, to calculate the displacement of the object 14. In this case, a displacement meter including the laser interferometer 1 is obtained. Also, the speed can be calculated from the displacement, and in this case, a speed meter including the laser interferometer 1 is obtained.

[0061] 2. Second Embodiment FIG. 4 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the second embodiment.

[0062] Hereinafter, the second embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 4, the same components as those in the first embodiment are denoted by the same reference numerals.

[0063] The interference optical system 50 shown in FIG. 4 is the same as the interference optical system 50 shown in FIG. 2 except that it includes a light intensity distribution adjuster 15.

[0064] The light intensity distribution adjuster 15 shown in FIG. 4 is arranged in the first non-coaxial portion NC1. This light intensity distribution adjuster 15 has a function of adjusting the intensity distribution in the cross section of the incident light. Thereby, a reference light L2 having a target light intensity distribution can be obtained. By interfering such a reference light L2 with the object light L3, a laser interferometer 1 with higher disturbance resistance against the displacement of the optical paths P2 and P3 can be realized. As the light intensity distribution adjuster 15, any optical component having the above function can be used. For example, an optical component called a beam shaper is used. The beam shaper adjusts the intensity distribution using optical elements such as lenses, diffraction gratings, and prisms.

[0065] The light intensity distribution adjuster 15 shown in FIG. 4 has an aspherical lens 151. By appropriately changing the lens shape of the aspherical lens 151, the light intensity distribution of the reference light L2 can be adjusted to a target distribution. An example of the target distribution is a top-hat type distribution. The top-hat type distribution is a distribution in which the light intensity is flatter than the Gaussian distribution. Therefore, by adjusting the light intensity distribution of the reference light L2 to the top-hat type distribution, the disturbance resistance against displacement can be particularly enhanced.

[0066] In addition, the light intensity distribution adjuster 15 shown in FIG. 4 is arranged at the subsequent stage of the light path expander 13. The subsequent stage refers to the direction in which light travels from the reference position. By arranging the light intensity distribution adjuster 15 at this position, the light intensity distribution of the reference light L2 with an expanded light path can be optimized. As a result, when the reference light L2 and the object light L3 are interfered with, the disturbance resistance against displacement can be particularly enhanced.

[0067] FIG. 5 is a conceptual diagram for explaining the operation and effect of the light intensity distribution adjuster 15 shown in FIG. 4. FIG. 5 shows images of the light intensity distribution when a displacement occurs in the optical paths P2 and P3 in the case where there is a light path expander 13 but no light intensity distribution adjuster 15, and in the case where there are both a light path expander 13 and a light intensity distribution adjuster 15. In this image, the horizontal axis indicates the respective light paths and positions of the reference light L2 and the object light L3, and the vertical axis indicates the light intensity. Therefore, each curve in FIG. 3 shows the respective light intensity distributions of the reference light L2 and the object light L3.

[0068] When there is a light path expander 13 but no light intensity distribution adjuster 15, the light intensity distribution of the reference light L2 has a Gaussian distribution shape as shown in FIG. 5, for example. For this reason, the light intensity contributing to interference decreases according to the amount of displacement, and the interference signal becomes small. As a result, since the S / N ratio of the received signal decreases, the disturbance resistance becomes low.

[0069] On the other hand, when the light intensity distribution adjuster 15 is arranged at the subsequent stage of the light path expander 13, the light intensity distribution of the reference light L2 can be adjusted to a top-hat type distribution as shown in FIG. 5. In this case, even if there is a slight displacement, the change in the light intensity contributing to interference can be particularly suppressed to be small, so that the influence of the displacement is hardly reflected in the S / N ratio of the received signal. Therefore, by providing the light intensity distribution adjuster 15, the disturbance resistance of the measurement accuracy can be particularly enhanced. Also in the second embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0070] 3. Third Embodiment FIG. 6 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the third embodiment.

[0071] Hereinafter, the third embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 6, the same components as those in the first embodiment are denoted by the same reference numerals.

[0072] The interference optical system 50 shown in FIG. 6 is the same as the interference optical system 50 shown in FIG. 2, except that the optical splitter 4 is a polarization beam splitter and the light receiving element 10 is composed of a differential amplification type light receiving module.

[0073] The optical splitter 4 shown in FIG. 6 is a polarization beam splitter and has a function of reflecting S-polarized light and transmitting P-polarized light. Specifically, the optical splitter 4 shown in FIG. 6 splits the emitted light L1 into a first split light L1a that is S-polarized and a second split light L1b that is P-polarized. With this function, the optical splitter 4 shown in FIG. 6 can easily suppress the light quantity loss when splitting the emitted light L1 into two. Thereby, in the laser interferometer 1 shown in FIG. 6, a decrease in the S / N ratio of the received signal due to the light quantity loss can be suppressed.

[0074] A half-wave plate 41 is disposed on the optical path P1 between the laser light source 2 and the optical splitter 4 shown in FIG. 6. The emitted light L1 emitted from the laser light source 2 is converted into linearly polarized light with an intensity ratio of S-polarized light and P-polarized light of, for example, 50:50 by passing through the half-wave plate 41.

[0075] A PBS 45 and a quarter-wave plate 42 are disposed on the optical path P1a between the optical splitter 4 and the optical modulator 12 shown in FIG. 6. The PBS 45 is a polarization beam splitter. The first split light L1a that is S-polarized and emitted from the optical splitter 4 is reflected by the PBS 45 and converted into circularly polarized light by the quarter-wave plate 42. This circularly polarized light is incident on the optical modulator 12 and becomes the reference light L2.

[0076] On the optical path P2 between the optical modulator 12 and the optical splitter 4 shown in Fig. 6, a quarter-wave plate 42, a PBS 45, a mirror 46, and an optical diameter expander 13 are arranged. The reference light L2 is converted into P-polarized light by the quarter-wave plate 42 and passes through the PBS 45. The reference light L2 that has passed through the PBS 45 is reflected by the mirror 46, and its optical diameter is expanded when it passes through the optical diameter expander 13. The reference light L2 with an expanded optical diameter passes through the optical splitter 4 and is mixed with the object light L3 in the optical path P4. At this time, a part of the reference light L2 may be reflected by the optical splitter 4 and head towards the laser light source 2 as the return light L5. If the return light L5 reaches the laser light source 2, the laser oscillation in the laser light source 2 may become unstable, and the quality of the emitted light L1 may deteriorate.

[0077] Therefore, it is preferable that the distance Δx between the center of the incident position 401 where the reference light L2 enters the optical splitter 4 and the center of the optical path P1 of the emitted light L1 (laser light) satisfies the following formula. (Φin + Φex) / 2 < Δx

[0078] In the above formula, Φin is the optical diameter of the emitted light L1, and Φex is the optical diameter of the reference light L2 after being expanded by the optical diameter expander 13. By making the distance Δx satisfy the above formula, even when the return light L5 is generated, the probability of the return light L5 reaching the laser light source 2 can be reduced. Thereby, the destabilization of the laser oscillation can be suppressed, and the decrease in the S / N ratio of the received signal due to the deterioration of the quality of the emitted light L1 can be suppressed.

[0079] On the optical path P1b between the optical splitter 4 and the object 14 shown in Fig. 6, a quarter-wave plate 43 is arranged. The second split light L1b, which is P-polarized light emitted from the optical splitter 4, is converted into circularly polarized light by the quarter-wave plate 43. This circularly polarized light is incident on the object 14 and becomes the object light L3.

[0080] On the optical path P3 between the object 14 shown in FIG. 6 and the optical splitter 4, a quarter-wave plate 43 and a mirror 47 are arranged. The object light L3 is converted into S-polarized light by the quarter-wave plate 43 and reflected once by the optical splitter 4. The object light L3 reflected by the optical splitter 4 is reflected by the mirror 47, enters the optical splitter 4 again and is reflected once more, and is mixed with the reference light L2 in the optical path P4. A half-wave plate 44 is arranged on the optical path P4. When the mixed light of the reference light L2 and the object light L3 passes through the half-wave plate 44, the polarization states are aligned. As a result, interference occurs between the reference light L2 and the object light L3, and the mixed light containing the interference signal enters the light-receiving element 10.

[0081] As described above, the light-receiving element 10 shown in FIG. 6 is composed of a differential amplification type light-receiving module. The light-receiving element 10 shown in FIG. 6 includes a first PD 101, a second PD 102, and a PBS 103. The first PD 101 and the second PD 102 are each a photodiode or the like. Also, a polarization beam splitter is preferably used for the PBS 103. The mixed light incident on the light-receiving element 10 is split into S-polarized light and P-polarized light by the PBS 103. The P-polarized light is received by the first PD 101, and the S-polarized light is received by the second PD 102. By using such a differential amplification type light-receiving module as the light-receiving element 10, the noise contained in the mixed light can be canceled or reduced, and the S / N ratio of the received signal can be particularly increased. Note that in the light-receiving element 10, each optical element does not have to be modularized. Also, from the viewpoint of making the optical path difference zero between the optical path on the first PD 101 side and the optical path on the second PD 102 side, the PBS 103 is preferably a cube type element. Also in the third embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0082] In addition, in this embodiment, a half-wave plate 41, 44, a quarter-wave plate 42, 43, a PBS 45, mirrors 46, 47, etc. are added to the interference optical system 50, and the incident angle and the emission angle of the laser light incident on the optical modulator 12 and the object 14 are equal. According to such a configuration, although the number of components of the interference optical system 50 increases, the attitude of the object 14 can be kept constant regardless of the working distance (the distance between the laser interferometer 1 and the object 14). Thereby, the usability of the laser interferometer 1 can be improved.

[0083] In addition, in this embodiment, the optical diameter expander 13 is arranged not in the second non-coaxial portion NC2 included in the optical path P3 but in the first non-coaxial portion NC1 included in the optical path P2. Since the optical path P2 is the optical path along which the reference light L2 travels, the optical path length is constant. Therefore, even when the beam of the reference light L2 spreads due to optical diffraction or the like, the optical diameter of the beam rarely increases unintentionally. Thus, in this embodiment, even if the return light L5 is generated, it is possible to suppress the optical diameter thereof from becoming extremely large, and it is possible to reduce the probability that the return light L5 reaches the laser light source 2.

[0084] In addition, in this embodiment, the differential amplification type light receiving module is not essential, and for example, the light receiving element 10 may be composed of one photodiode.

[0085] 4. Fourth Embodiment FIG. 7 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the fourth embodiment.

[0086] Hereinafter, the fourth embodiment will be described. In the following description, the differences from the third embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 7, the same components as those in the third embodiment are denoted by the same reference numerals.

[0087] The interference optical system 50 shown in FIG. 7 is the same as the interference optical system 50 shown in FIG. 6 except for the arrangement of the optical diameter expander 13.

[0088] On the optical path P1a between the optical splitter 4 and the optical modulator 12 shown in FIG. 7, a PBS 45 and a quarter-wave plate 42 are arranged. The first split light L1a emitted from the optical splitter 4 is reflected by the PBS 45, passes through the quarter-wave plate 42, and becomes the reference light L2 at the optical modulator 12. On the optical path P2 between the optical modulator 12 and the optical splitter 4 shown in FIG. 7, a quarter-wave plate 42, a PBS 45, and a mirror 46 are arranged. The reference light L2 passes through the quarter-wave plate 42 and the PBS 45, is reflected by the mirror 46, and then passes through the optical splitter 4 without passing through the optical path expander 13.

[0089] On the other hand, on the optical path P1b between the optical splitter 4 and the quarter-wave plate 43 shown in FIG. 7, a PBS 48 and a quarter-wave plate 43 are arranged. The PBS 48 is a polarization beam splitter. The second split light L1b emitted from the optical splitter 4 shown in FIG. 7 passes through the PBS 48 and the quarter-wave plate 43 and becomes the object light L3 at the object 14. On the optical path P3 between the object 14 and the optical splitter 4 shown in FIG. 7, a quarter-wave plate 43 and a PBS 48 are arranged. The object light L3 passes through the quarter-wave plate 43 and is reflected by the PBS 48.

[0090] Also, in FIG. 7, the arrangements of the optical path expander 13 and the mirror 47 are different from those in FIG. 6. A mirror 47 and an optical path expander 13 are arranged in a part (the second non-coaxial portion NC2) of the optical path P3 shown in FIG. 7. The object light L3 reflected by the PBS 48 is reflected by the mirror 47 and then enters the optical path expander 13, and its optical path is expanded. The object light L3 with an expanded optical path is reflected by the optical splitter 4 and mixed with the reference light L2 in the optical path P4.

[0091] When the object light L3 is reflected by the optical splitter 4, a part of the object light L3 may pass through the optical splitter 4 and go toward the laser light source 2 as the return light L6. The incident position 402 where the object light L3 enters the optical splitter 4 is the same as the incident position 401 where the reference light L2 enters the optical splitter 4. Therefore, also in this embodiment, it is preferable that the distance Δx satisfies the following formula. (Φin + Φex) / 2 < Δx

[0092] By having the distance Δx satisfy the above formula, even when the return light L6 is generated, the probability of the return light L6 reaching the laser light source 2 can be reduced. Also in the fourth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0093] In this embodiment, among the emitted light L1 incident on the optical splitter 4, the S-polarized light reflected by the optical splitter 4 becomes the first split light L1a. In such a configuration, the reference light L2 becomes P-polarized light and returns to the optical splitter 4, passes through the optical splitter 4, and is incident on the light receiving element 10. At this time, when the optical splitter 4 is a plate-type element, the probability that the P-polarized light is reflected without passing through is higher than the probability that the S-polarized light is transmitted without being reflected. However, in this embodiment, since the P-polarized light is the reference light L2 generated by the optical modulator 12, the divergence angle of the beam is more limited than when the P-polarized light is the object light L3. Therefore, in this embodiment, as shown in FIG. 7, even when a part of the reference light L2 becomes the return light L5, the optical path diameter of the return light L5 can be sufficiently reduced, and thus the probability of the return light L5 reaching the laser light source 2 can be reduced.

[0094] Note that the distance Δx between the center of the incident position 401 where the reference light L2 is incident on the optical splitter 4 and the center of the optical path P1 of the emitted light L1 (laser light) preferably satisfies the following formula. Φin < Δx

[0095] In the above formula, Φin is the optical path diameter of the emitted light L1. By having the distance Δx satisfy the above formula, even when the return light L5 is generated, the probability of the return light L5 reaching the laser light source 2 can be reduced. Also, the range in which the distance Δx can be taken in the above formula is wider than the range in which the distance Δx can be taken in the formula defined in the third embodiment. Therefore, this embodiment is also useful in that the constraint on the distance Δx is relatively loose. When the constraint on the distance Δx is loose, the space saving of the interference optical system 50 can be achieved.

[0096] In this embodiment, the P-polarized light transmitted through the optical splitter 4 becomes the second split light L1b, and after passing through the object 14, it becomes S-polarized light and passes through the optical path expander 13. As described above, in the optical splitter 4, the probability that the S-polarized light is transmitted without being reflected is lower than the probability that the P-polarized light is reflected without being transmitted. Therefore, in this embodiment, as shown in FIG. 7, the probability that a part of the object light L3 becomes the return light L6 can be sufficiently reduced.

[0097] 5. Fifth Embodiment FIG. 8 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the fifth embodiment.

[0098] Hereinafter, the fifth embodiment will be described. In the following description, the differences from the third and fourth embodiments will be mainly described, and the description of the same matters will be omitted. In FIG. 8, the same components as those in the third and fourth embodiments are denoted by the same reference numerals.

[0099] The interference optical system 50 shown in FIG. 8 is the same as the interference optical system 50 shown in FIG. 7, except that the relative positions of the optical modulator 12 and the object 14 with respect to the optical splitter 4 are interchanged.

[0100] The second split light L1b emitted from the optical splitter 4 shown in FIG. 8 is reflected by the PBS 45, passes through the quarter-wave plate 42, and becomes the object light L3 at the object 14. The object light L3 passes through the quarter-wave plate 42 and the PBS 45, is reflected by the mirror 46, and then passes through the optical path expander 13 without passing through it, passes through the optical splitter 4, and is mixed with the reference light L2.

[0101] On the other hand, the first split light L1a emitted from the optical splitter 4 shown in FIG. 8 passes through the PBS 48 and the quarter-wave plate 43 and becomes the reference light L2 at the optical modulator 12. The reference light L2 passes through the quarter-wave plate 43 and is reflected by the PBS 48. The reference light L2 reflected by the PBS 48 is reflected by the mirror 47, then enters the optical path expander 13, and the optical path is expanded. The reference light L2 with the expanded optical path is reflected by the optical splitter 4 and mixed with the object light L3.

[0102] Also in the fifth embodiment as described above, the same effects as those of the third embodiment can be obtained. Specifically, the incident angle and the emission angle of the laser light incident on the optical modulator 12 and the object 14 are equal. Thereby, the usability of the laser interferometer 1 can be improved.

[0103] Further, in the present embodiment, the reference light L2 is configured to be incident on the optical path expander 13. Therefore, since the optical path length of the optical path P2 of the reference light L2 incident on the optical path expander 13 is constant, there is no possibility of unintentional spreading. Thus, in the present embodiment, it is easy to suppress a decrease in the S / N ratio of the received signal due to the expansion of the optical path of the reference light L2 incident on the optical path expander 13.

[0104] 6. Effects of the Embodiment As described above, the laser interferometer 1 according to the embodiment includes a laser light source 2, an optical splitter 4, an optical modulator 12, a light receiving element 10, and an optical path expander 13. The laser light source 2 emits emitted light L1 (laser light). The optical splitter 4 splits the emitted light L1 into a first split light L1a and a second split light L1b. The optical modulator 12 modulates the frequency of the first split light L1a to generate the reference light L2. The light receiving element 10 receives the object light L3 generated by reflecting the second split light L1b from the object 14 and the reference light L2. The optical path expander 13 expands the optical path of the incident light. Further, the laser interferometer 1 according to the embodiment is configured such that the optical path P2 of the reference light L2 includes a first non-coaxial portion NC1 that is displaced from the optical path P1a of the first split light L1a, or the optical path P3 of the object light L3 includes a second non-coaxial portion NC2 that is displaced from the optical path P1b of the second split light L1b. And the optical path expander 13 is disposed in the first non-coaxial portion NC1 or the second non-coaxial portion NC2.

[0105] According to such a configuration, since the optical path of either the reference light L2 or the object light L3 is extended, it becomes easier to secure an area where both overlap and interfere, and the interference state is likely to be maintained even when disturbances such as vibration and shock are applied. Therefore, the signal-to-noise ratio of the received light signal is less likely to decrease. In addition, the optical path expander 13 is sufficiently small and lightweight, and a feedback mechanism for detecting disturbances and reflecting them in the measurement is unnecessary. Therefore, according to the above configuration, miniaturization is easy, the measurement accuracy is less likely to decrease even when disturbances are applied, and the laser interferometer 1 with excellent usability can be realized.

[0106] Further, the laser interferometer 1 according to the above embodiment includes an optical intensity distribution adjuster 15. The optical intensity distribution adjuster 15 adjusts the intensity distribution in the cross section of the incident light.

[0107] According to such a configuration, for example, when the optical path expander 13 is arranged in the first non-coaxial portion NC1, the reference light L2 having the target optical intensity distribution can be obtained. By interfering such reference light L2 with the object light L3, a laser interferometer 1 with higher disturbance resistance can be realized.

[0108] Further, in the laser interferometer 1 according to the above embodiment, the optical intensity distribution adjuster 15 is arranged at the subsequent stage of the optical path expander 13.

[0109] According to such a configuration, for example, when the optical path expander 13 is arranged in the first non-coaxial portion NC1, the optical intensity distribution of the reference light L2 with an extended optical path can be optimized. Thereby, when the reference light L2 and the object light L3 are interfered, the disturbance resistance against displacement can be particularly enhanced.

[0110] Further, in the laser interferometer 1 according to the above embodiment, the optical intensity distribution adjuster 15 has a function of flattening the intensity distribution of the emitted light compared to the intensity distribution of the incident light.

[0111] According to such a configuration, the influence of the misalignment of the optical path is hardly reflected in the signal-to-noise ratio of the received light signal. Therefore, it is possible to realize the laser interferometer 1 with particularly enhanced disturbance resistance against misalignment.

[0112] Further, in the laser interferometer 1 according to the above embodiment, of the reference light L2 and the object light L3, one of the lights passes through the optical path expander 13 and the optical path is expanded, and the other light is configured such that the optical path is not expanded. Then, when the optical path of the emitted light L1 (laser light) is Φin, and the distance between the center of the incident position where the other light enters the optical splitter 4 and the center of the optical path P1 of the emitted light L1 is Δx, Φin < Δx is satisfied.

[0113] According to such a configuration, even when the other light becomes the return light L5, the probability that the return light L5 reaches the laser light source 2 can be reduced.

[0114] Further, in the laser interferometer 1 according to the above embodiment, of the reference light L2 and the object light L3, one of the lights passes through the optical path expander 13 and the optical path is expanded, and the other light is configured such that the optical path is not expanded. Then, when the optical path of the emitted light L1 (laser light) is Φin, the optical path of one of the lights after being expanded by the optical path expander 13 is Φex, and the distance between the center of the incident position where one of the lights enters the optical splitter 4 and the center of the optical path P1 of the emitted light L1 is Δx, (Φin + Φex) / 2 < Δx is satisfied.

[0115] According to such a configuration, even when one of the lights becomes the return light L6, the probability that the return light L6 reaches the laser light source 2 can be reduced.

[0116] Further, in the laser interferometer 1 according to the above embodiment, the optical splitter 4 has a function of splitting the emitted light L1 (laser light) by transmission and reflection. And the light transmitted through the optical splitter 4 is configured to pass through the optical path expander 13 via the optical modulator 12 or the object 14.

[0117] According to such a configuration, since the probability that the light passing through the optical path expander 13 is transmitted through the optical splitter 4 without being reflected is low, the probability of generating the return light L6 can be sufficiently reduced.

[0118] Also, in the laser interferometer 1 according to the above embodiment, the optical splitter 4 is a polarization beam splitter.

[0119] According to such a configuration, it is easy to suppress the light quantity loss when splitting the emitted light L1 (laser light) into two. Therefore, a decrease in the S / N ratio of the received signal due to the light quantity loss can be suppressed.

[0120] As described above, the laser interferometer of the present invention has been described based on the illustrated embodiment. However, the laser interferometer of the present invention is not limited to the above embodiment, and the configuration of each part can be replaced with any configuration having the same function. Further, any other arbitrary components may be added to the laser interferometer according to the above embodiment.

[0121] Also, the laser interferometer of the present invention may have a configuration in which two or more of the above embodiments are combined. For example, an optical intensity distribution adjuster may be added to the third to fifth embodiments.

[0122] Furthermore, the laser interferometer of the present invention is applicable not only to the displacement meter and speed meter described above, but also to, for example, a vibration meter, an inclinometer, a distance meter (length measuring instrument), etc. Also, as applications of the laser interferometer of the present invention, there are optical communication interference measurement techniques that enable distance measurement, 3D imaging, spectroscopy, etc., an optical fiber gyro that realizes an angular velocity sensor, an angular acceleration sensor, etc., and a Fourier spectrometer equipped with a moving mirror device such as a Fourier spectroscopic analyzer and a shape measuring device.

[0123] Among these, the Fourier spectroscopic analyzer can be applied to, for example, FT-IR (Fourier transform infrared spectroscopy) devices, FT-NIR (Fourier transform near-infrared spectroscopy) devices, FT-VIS (Fourier transform visible spectroscopy) devices, FT-UV (Fourier transform ultraviolet spectroscopy) devices, FT-THz (Fourier transform terahertz spectroscopy) devices, etc.

[0124] In addition, the shape measurement device can be applied to, for example, white light interference shape measurement devices, optical coherence tomography (OCT) imaging devices, etc.

[0125] Also, two or more of the laser light source, the optical modulator, and the light receiving element may be mounted on the same substrate. Thereby, miniaturization and weight reduction of the interference optical system can be easily achieved, and the ease of assembly can be enhanced.

[0126] Moreover, although the above-described embodiment has a so-called Michelson-type interference optical system, the laser interferometer of the present invention can also be applied to those having other types of interference optical systems, for example, Mach-Zehnder-type interference optical systems.

Description of Reference Numerals

[0127] 1... Laser interferometer, 2... Laser light source, 4... Optical splitter, 10... Light receiving element, 12... Optical modulator, 13... Optical path expander, 14... Object, 15... Light intensity distribution adjuster, 30... Vibration element, 41... 1 / 2 wavelength plate, 42... 1 / 4 wavelength plate, 43... 1 / 4 wavelength plate, 44... 1 / 2 wavelength plate, 45... PBS, 46... Mirror, 47... Mirror, 48... PBS, 50... Interference optical system, 51... Sensor head unit, 52... Demodulation arithmetic unit, 53... Pretreatment unit, 54... Demodulation processing unit, 55... Demodulated signal output unit, 59... Main body unit, 60... Signal generation unit, 61... Oscillation circuit, 101... First PD, 102... Second PD, 103... PBS, 131... First lens, 132... Second lens, 151... Aspherical lens, 401... Incident position, 402... Incident position, IF... Interference region, L1... Emitted light, L1a... First split light, L1b... Second split light, L2... Reference light, L3... Object light, L5... Return light, L6... Return light, NC1... First non-coaxial part, NC2... Second non-coaxial part, P1... Optical path, P1a... Optical path, P1b... Optical path, P2... Optical path, P3... Optical path, P4... Optical path, Δx... Distance, Φin... Optical path, Φex... Optical path

Claims

1. A laser light source that emits laser light, An optical splitter that splits the laser light into a first split light and a second split light, An optical modulator that modulates the frequency of the first split light to generate a reference light, A light receiving element that receives the object light generated by reflecting the second split light from an object and the reference light, An optical path expander that expands the optical path of the incident light, Comprising, The optical path of the reference light is configured to include a first non-coaxial portion that is displaced from the optical path of the first split light, or the optical path of the object light is configured to include a second non-coaxial portion that is displaced from the optical path of the second split light, The laser interferometer, wherein the optical path expander is disposed in the first non-coaxial portion or the second non-coaxial portion.

2. The laser interferometer according to claim 1, further comprising an optical intensity distribution adjuster that adjusts the intensity distribution in the cross section of the incident light.

3. The laser interferometer according to claim 2, wherein the optical intensity distribution adjuster is disposed downstream of the optical path expander.

4. The laser interferometer according to claim 3, wherein the optical intensity distribution adjuster has a function of flattening the intensity distribution of the emitted light more than the intensity distribution of the incident light.

5. Of the reference light and the object light, one light is configured to pass through the optical path expander and have its optical path expanded, and the other light is configured not to have its optical path expanded, Let the optical path of the laser light be Φin, When the distance between the center of the incident position where the other light enters the optical splitter and the center of the optical path of the laser light is Δx, The laser interferometer according to claim 1, satisfying Φin < Δx.

6. Of the reference light and the object light, one light is configured to pass through the optical path expander and have its optical path expanded, and the other light is configured not to have its optical path expanded, Let the optical path of the laser light be Φin, Let the optical path of the one light after being expanded by the optical path expander be Φex, When the distance between the center of the incident position where the one light enters the optical splitter and the center of the optical path of the laser light is Δx, The laser interferometer according to claim 1, satisfying (Φin + Φex) / 2 < Δx.

7. The optical splitter has a function of splitting the laser light by transmission and reflection, The laser interferometer according to claim 1, wherein the light transmitted through the optical splitter is configured to pass through the optical path expander via the optical modulator or the object.

8. The laser interferometer according to claim 1, wherein the optical splitter is a polarization beam splitter.

Images