JP2015203592A - Laser doppler measurement device and measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser Doppler measurement device and measurement method capable of measuring a long distance.SOLUTION: A laser Doppler measurement device according to an embodiment of the present invention comprises: a PBS for branch 16 which generates a reference laser beam and an irradiation laser beam irradiating a measurement target object 5 by branching a laser beam; a PBS 17 which is provided between the PBS for branch 16 and the measurement target object 5 and receives a reflection laser beam reflected by the measurement target object 5; a reflection type λ/4 plate 21 which reflects the irradiation laser beam and the reflection laser beam; an AOM 31 which shifts the frequency of the reference laser beam; a half mirror for synthesis 33 which synthesizes the reference laser beam and the reflection laser beam to generate a synthetic light beam; a detector 38 which detects the synthetic light beam; and a processing device 63 which calculates oscillation of the measurement target object on the basis of an output signal from the detector 38.

Description

  The present invention relates to a laser Doppler measuring apparatus and a measuring method.

  Visual and hammering inspections are widely used to detect damage to structures. However, visual inspection and hammering inspection have problems in work safety. For example, it becomes difficult to inspect a structure that cannot secure safety in a severe radiation environment or work place.

  In addition, a method using a laser Doppler velocimeter has been developed for damage detection of structures (Non-Patent Documents 1 and 2). By using a laser Doppler velocimeter, non-contact inspection is possible. Further, since damage to the structure can be detected by performing laser Doppler measurement, the laser Doppler velocimeter is a very effective means for detecting the degree of deterioration of the structure.

  Note that Patent Document 1 discloses a laser Doppler vibrometer that measures a vibration state of a measurement object using an S wave and a P wave. The laser beam is separated into a P wave and an S wave by a PBS (polarization beam splitter). Then, the P wave becomes reference laser light, and the S wave becomes irradiation laser light. The measurement target is irradiated with an irradiation laser beam that is an S wave.

  A λ / 4 plate is disposed between the PBS and the measurement target. Therefore, the reflected laser beam reflected by the measurement object becomes a P wave and is combined with the reference laser beam. Then, the combined light obtained by combining the reference laser beam and the reflected laser beam is detected.

Japanese Patent Laid-Open No. 11-73809

Detecting voids in concrete structures focusing on local vibration characteristics Kiyoyuki Kaido, Masato Abe, Yozo Fujino, Kazuhiro Kumasaka Journal of Japan Society of Civil Engineers 690 / V-53.121-132, November 2001 Construction of laser microtremor measurement method and application to structural damage detection Kiyoyuki Kaido, Masato Abe, Yozo Fujino, Kazuhiro Kumasaka JSCE Proceedings No. 689 / I-57.183-199, October 2001

  However, the current laser Doppler vibrometer (velocimeter) has a maximum measurement distance of about 100 m. When the measurement distance is short, it is necessary to install a laser Doppler vibrometer near the structure. When the measurement object is in a radiation environment, it is difficult to install a laser Doppler vibrometer. In addition, when the measurement object is a bridge or a large building, the measurement device needs to be installed at a high place. Therefore, there is a possibility that it cannot be measured safely.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a laser Doppler measuring device and a measuring method having a long measuring distance.

  A laser Doppler measurement apparatus according to an aspect of the present embodiment generates a reference laser beam and an irradiation laser beam irradiated on a measurement object by branching the laser beam from the laser beam source and the laser beam source. 1 polarization beam splitter, a second polarization beam splitter that receives the irradiation laser beam and receives a reflected laser beam reflected by the measurement object, the second polarization beam splitter, and the measurement object A reflective λ / 4 plate that reflects the irradiation laser light and the reflected laser light, a frequency shifter that shifts the frequency of the reflected laser light from the second polarizing beam splitter, The reflected laser beam frequency-shifted by a frequency shifter is combined with the reference laser beam to generate a combined beam, and the combined beam is detected. And output unit, based on the detection result in the detector, a processor for calculating the vibration of the measurement object, but with the. Thereby, since an optical noise can be reduced, a measurement distance can be lengthened.

  The laser Doppler measurement apparatus includes a convex mirror on which the irradiation laser light from the second polarization beam splitter is incident, and a concave mirror that reflects the irradiation laser light reflected by the convex mirror and collects the light on the measurement object. And may be further provided. Thereby, since an optical noise can be reduced, a measurement distance can be lengthened.

  The laser Doppler measurement apparatus may further include a driving unit that moves the convex mirror together with the reflective λ / 4 plate to adjust the focal position of the irradiation laser light. By doing so, the focal position can be adjusted.

  In the laser Doppler measurement apparatus, an adaptive optical element may be provided on the concave mirror. Thereby, optical aberration, that is, noise can be reduced, and the measurement distance can be lengthened.

  In the laser Doppler measurement apparatus, the irradiation laser light may have a wavelength of 1532 nm. Thereby, the loss due to the absorption of the laser beam of moisture in the atmosphere can be reduced, so that the measurement distance can be lengthened.

  The laser Doppler measurement apparatus may further include a visible laser light source that emits a visible laser beam that is irradiated on the measurement object coaxially with an infrared laser beam. By doing so, the optical system can be easily adjusted.

  The laser Doppler measurement apparatus may further include an optical scanner that has a reflective surface that reflects the laser light, and that scans the laser light by changing an angle of the reflective surface. By doing so, the laser beam can be easily scanned.

  A laser Doppler measurement method according to an aspect of the present embodiment, a step in which a laser light source emits laser light, and a first polarization beam splitter branches the laser light, so that the reference laser light and the measurement object are irradiated. Generating a laser beam to be irradiated, a step of making the laser beam incident on a second polarization beam splitter, and reflecting the laser beam irradiated from the second polarization beam splitter by a reflective λ / 4 plate Irradiating the measurement object with the irradiation laser light reflected by the reflection type λ / 4, and reflecting the reflection laser light reflected by the measurement object by the reflection type λ / 4, , Causing the reflected laser light reflected by the reflective λ / 4 plate to enter the second polarizing beam splitter, and the second polarizing beam sp. A step of shifting the frequency of the reflected laser light from the scatter, a synthesis step of synthesizing the frequency-shifted reflected laser light with the reference laser light to generate a synthesized light, and a step of detecting the synthesized light And calculating the vibration of the measurement object based on the detection result of the combined light.

  According to the present invention, it is an object to provide a laser Doppler measuring apparatus and a measuring method having a long measuring distance.

It is a figure which shows the whole structure of the measurement system using the laser Doppler vibrometer concerning this Embodiment. It is a figure which shows the optical system of the laser Doppler vibrometer concerning this Embodiment. It is a top view which shows the compensation optical element used for a laser Doppler vibrometer. It is side surface sectional drawing which shows the compensation optical element used for a laser Doppler vibrometer.

  Hereinafter, a specific configuration of the present embodiment will be described with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals indicate substantially the same contents.

Embodiment 1 FIG.
A laser Doppler vibrometer according to the present embodiment and a structure measurement method using the same will be described with reference to the drawings. FIG. 1 is a diagram illustrating an overall configuration of a measurement system for measuring a structure. In addition, as a structure used as the measuring object 5, a building, a building such as a hospital or a school, a bridge, an elevated road, a power plant, a plant, and the like are exemplified, but the structure is not particularly limited.

  The operator 6 moves to the periphery of the measurement object 5 by the automobile 4 equipped with the laser Doppler vibrometer 1 and the gas cylinder 3. Then, the operator 6 installs the laser Doppler vibrometer 1. The operator 6 may move to the position within the measurement distance from the measurement object 5 and install the laser Doppler vibrometer 1. Since the measurement distance of the laser Doppler vibrometer 1 is 1 km or more, measurement from a distant place is possible.

  Since the measurement distance of the laser Doppler vibrometer 1 is very long, it is easy to secure the installation location. Furthermore, even if the measurement object 5 is in a dangerous environment such as a radiation environment or a high temperature environment, the laser Doppler vibrometer 1 can be installed at a remote position. Even if the measurement object 5 is a large structure, the laser Doppler vibrometer 1 does not need to be installed at a high place, so that the operator 6 does not have to work in a dangerous environment. Thereby, it can measure more safely and efficiently. Furthermore, since the operator 6 can perform measurement while riding on the automobile 4, safety can be ensured. Measurements can be performed safely even in an environment where a nuclear accident has occurred.

  The gas cylinder 3 supplies the gas of the laser Doppler vibrometer 1 at the time of measurement. The gas in the gas cylinder 3 is nitrogen or air. By ejecting the gas from the gas cylinder 3 to the laser Doppler vibrometer 1, dust and dust can be prevented from entering the laser Doppler vibrometer 1.

  The power source of the laser Doppler vibrometer 1 can be taken from the battery 2 of the automobile 4. That is, the laser Doppler vibrometer 1 is operated by the DC power supplied from the battery 2. As the automobile 4, it is preferable to use an electric car having a large capacity of the battery 2, a plug-in hybrid car, a hybrid car, or the like. By doing so, measurement in a state where the engine of the automobile 4 is stopped becomes possible. For example, a lithium ion battery can be used as the battery 2. It is desirable to supply DC power directly from the battery 2. By using only the DC power supply without using the AC power supply, the influence of AC noise, switching noise, and the like can be reduced. Therefore, it can measure more correctly.

  Next, the configuration of the laser Doppler vibrometer 1 will be described with reference to FIG. FIG. 2 is a diagram showing an overall configuration of the laser Doppler vibrometer 1. The laser Doppler vibrometer 1 includes a main body 101 in which an optical system is disposed, an AOM driver 61, a demodulator 62, a processing device 63, a controller 64, and the like.

  The main body 101 is installed at a location sufficiently away from the measurement target. The main body 101 has a case that houses a light source, a detector, a lens, a mirror, a half mirror, a scanner, a polarization beam splitter (hereinafter, PBS), and the like. The operator 6 installs the main body 101 in the automobile 4.

  The main body 101 includes an infrared laser light source 11, a visible laser light source 71, and a laser range finder 91. The infrared laser light source 11 constitutes an optical heterodyne laser Doppler vibrometer. Infrared laser light from the infrared laser light source 11 is used in a laser Doppler vibrometer. Therefore, the infrared laser light from the infrared laser light source 11 is applied to the measurement object 5 via the optical system in the main body 101. In the main body 101, the signal light reflected by the measurement object 5 and the reference light are combined. Then, the vibration frequency of the measurement object 5 is detected by causing the reflected laser beam and the reference laser beam to overlap and interfere with each other.

  The visible laser light source 71 is provided for confirming the alignment of the laser light and the irradiation position of the infrared laser light from the infrared laser light source 11. That is, the visible laser light from the visible laser light source 71 is coaxial with the infrared laser light from the infrared laser light source 11 by the optical system in the main body 101. Then, the visible laser light from the visible laser light source 71 irradiates the measurement object 5. The laser range finder 91 is provided to detect the approximate distance to the measurement object 5 and the measurement position. The wavefront sensor 93 is provided in order to correct the wavefront by an adaptive optics element 27 described later.

  First, the measurement optical system of the infrared laser light source 11 will be described. In the following description, the light emitted from the infrared laser light source 11 and irradiated on the measurement object 5 is referred to as irradiation laser light, and the light reflected by the measurement object 5 and incident on the detector 38 is reflected laser. Let it be light.

  The infrared laser light source 11 is a laser light source that emits coherent infrared laser light. Irradiation laser light from the infrared laser light source 11 passes through the fiber 12 and enters the lens 13. The lens 13 converts the irradiated laser light into a parallel light beam. The irradiated laser light that has become a parallel light beam by the lens 13 passes through the isolator 14 and enters the wavelength conversion means 18. The isolator 14 is provided so that the return light does not enter the infrared laser light source 11.

  The wavelength conversion means 18 is a tunable filter or the like, and sets the wavelength of the irradiation laser light to 1532 nm. By setting the irradiation laser beam to a wavelength of 1532 nm, loss due to absorption in the air can be reduced, and long-distance propagation is possible. The infrared laser light having a wavelength of 1532 nm by the wavelength conversion means 18 is incident on the Gran Thompson prism 15.

  The Grand Thompson prism 15 is a polarizing prism made of calcite and has a high extinction ratio. The Gran Thompson prism 15 has an extinction ratio of 1000000: 1, for example. The linearly polarized irradiation laser light that has passed through the Glan-Thompson prism 15 enters the branching PBS 16. The branching PBS 16 branches the irradiated laser light according to the polarization state. Therefore, the P-polarized component (hereinafter referred to as P wave) of the irradiation laser light passes through the branching PBS 16, and the S-polarized component (hereinafter referred to as S wave) is reflected by the branching PBS 16. The S wave becomes signal light irradiated on the measurement object 5, and the P wave becomes reference light not irradiated on the measurement object 5. As will be described later, the signal light and the reference light are combined and detected by the detector 38.

  First, the optical path of signal light will be described. The S wave reflected by the branching PBS 16 enters the PBS 17. The PBS 17 reflects or transmits light according to the polarization state. The PBS 17 reflects the S wave and transmits the P wave. Therefore, the S wave reflected by the PBS 17 travels in the direction of the reflective λ / 4 plate 21.

  The reflective λ / 4 plate 21 reflects the S wave from the PBS 17 in the direction of the convex mirror 22. Further, the reflective λ / 4 plate 21 gives a phase difference of ¼ wavelength between a component perpendicular to the optical axis and a component parallel to the optical axis. Therefore, the irradiation laser light reflected by the reflective λ / 4 plate 21 is converted into circularly polarized light. The circularly polarized irradiation laser light reflected by the reflective λ / 4 plate 21 is incident on the convex mirror 22.

  The convex mirror 22 reflects the irradiation laser light in the direction of the concave mirror 23. The irradiated laser light reflected by the convex mirror 22 travels toward the concave mirror 23 while spreading. The irradiated laser light reflected by the concave mirror 23 travels in the direction of the polygon mirror 24 while being narrowed down. The concave mirror 23 and the convex mirror 22 are disposed so that the reflecting surfaces thereof face each other. Therefore, only the light that has passed through the outside of the convex mirror 22 out of the irradiated laser light reflected by the concave mirror 23 enters the polygon mirror 24. That is, the light on the central axis of the concave mirror 23 is incident on the convex mirror 22 and therefore does not reach the polygon mirror 24.

  The polygon mirror 24 is a first optical scanner and scans the irradiation laser light in the first direction. That is, when the polygon mirror 24 rotates, the reflection direction of the irradiation laser light changes. Thereby, the irradiation position of the reflected laser beam on the measurement object 5 can be scanned. The irradiated laser light reflected by the polygon mirror 24 enters the galvanometer mirror 25. The galvanometer mirror 25 is a second optical scanner, and scans the irradiation laser light in the second direction. Then, the irradiation laser light reflected by the galvanometer mirror 25 passes through the opening 28 of the main body 101 and enters the measurement object 5.

  For example, the polygon mirror 24 scans the irradiation position of the irradiation laser beam on the measurement object 5 in the X direction, and the galvano mirror 25 scans the irradiation position in the Y direction orthogonal to the X direction. Thus, the laser Doppler vibrometer 1 uses the two optical scanners to scan the surface of the measurement object 5 two-dimensionally. Therefore, it is possible to measure vibrations in a certain region of the measurement object 5. The optical scanner is not limited to the polygon mirror 24 and the galvanometer mirror 25. Two galvanometer mirrors 25 may be used as the optical scanner. The optical scanner has a reflecting surface that reflects the laser beam, and scans the laser beam by changing the angle of the reflecting surface.

  The irradiation laser light applied to the measurement object 5 is reflected by the measurement object 5 and becomes reflected laser light. The frequency of the reflected laser light changes due to the Doppler shift. That is, the reflected laser beam has a frequency different from that of the irradiation laser beam due to the vibration component of the measurement object 5. For example, if the reference frequency corresponding to the irradiation laser light (λ = 1532 nm) of the infrared laser light source 11 is fs and the frequency of the vibration component is fd, the frequency of the reflected laser light is fs ± fd.

  The convex mirror 22 and the concave mirror 23 constitute an optical system similar to the Schmitt Newton telescope. The concave mirror 23 condenses the irradiation laser light on the measurement object 5. That is, the irradiation laser light reflected by the concave mirror 23 advances while being narrowed down so that the surface of the measurement object 5 becomes the condensing position of the irradiation laser light. Furthermore, in this embodiment, a linear drive device 50 is provided to adjust the focal position.

  The linear drive device 50 includes a servo motor 51, a linear guide 52, and a base 53. The reflective λ / 4 plate 21 and the convex mirror 22 are fixed to the base 53. The linear guide 52 supports the base 53 so as to be movable. As the servo motor 51 rotates, the base 53 moves linearly along the linear guide 52. Thus, the reflective λ / 4 plate 21 and the convex mirror 22 provided on the base 53 move in the direction of the arrow A.

  By the linear drive device 50, the convex mirror 22 and the concave mirror 23 approach or separate. As the distance between the convex mirror 22 and the concave mirror 23 changes, the focal position of the irradiation laser light changes along the optical axis. Thus, the focal position can be adjusted by moving the convex mirror 22 relative to the concave mirror 23. Therefore, the light can be condensed on the surface of the measurement object 5. Furthermore, since the convex mirror 22 and the reflective λ / 4 plate 21 are moved together, the focal position can be easily adjusted.

  An adaptive optical element 27 is provided on the back side of the concave mirror 23. The compensation optical element 27 is provided to correct the wavefront of the reflected laser light. The configuration of the compensation optical element 27 will be described later.

  An opening 28 for passing the irradiation laser light reflected by the galvanometer mirror 25 is provided in the main body 101 which is a case. And gas is supplied to the opening part 28 so that dust and dust may not enter from the opening part 28. That is, during the measurement, nitrogen gas is allowed to flow from the inside to the outside of the main body 101 that is the case. For example, the gas cylinder 3 shown in FIG. 1 supplies nitrogen gas. By doing so, it is possible to prevent dust and dirt from entering the main body 101 from the opening 28. Therefore, highly accurate measurement is possible.

  The signal light is reflected by the measurement object 5 and propagates through the optical system described above. That is, the reflected laser light propagates in the opposite direction to the irradiation laser light. The reflected laser light is descanned by the galvanometer mirror 25 and the polygon mirror 24. The reflected laser light reflected by the galvanometer mirror 25 and the polygon mirror 24 is reflected by the concave mirror 23 and the convex mirror 22. Then, the reflected laser light reflected by the concave mirror 23 and the convex mirror 22 enters the reflective λ / 4 plate 21.

  In the reflection type λ / 4 plate 21, the reflected laser beam which is circularly polarized light is reflected by the reflection type λ / 4 plate 21 to become a P wave. That is, since the infrared laser light is reflected by the reflection type λ / 4 plate 21 in two reciprocations, it is converted from S waves to P waves. The reflected laser light that has become the P wave passes through the PBS 17 and enters an AOM (Acoustic Optical Modulator) 31. Thus, the PBS 17 is arranged in the optical path from the branching PBS 16 to the reflective λ / 4 plate 21. The PBS 17 receives the irradiated laser light from the branching PBS 16 and receives the reflected laser light from the reflective λ / 4 plate 21.

  The AOM 31 modulates the frequency of the reflected laser beam. For example, the AOM 31 is driven at 80 MHz by the AOM driver 61. For example, if the reference frequency corresponding to the irradiation laser light (λ = 1532 nm) of the infrared laser light source 11 is fs, the frequency of the vibration component of the measurement object 5 is fd, and the modulation frequency of the AOM 31 is 80 MHz, the frequency from the AOM 31 The frequency of the reflected laser light is fs ± fd + 80 MHz. The AOM 31 functions as a frequency shifter. When the FM frequency becomes measurement noise, the modulation frequency of the AOM 31 can be set to 240 MHz.

  The reflected laser light frequency-modulated by the AOM 31 is reflected by the mirror 32 and is incident on the synthesizing half mirror 33. The synthesizing half mirror 33 transmits part of the incident light and reflects the rest. The half mirror reflects or transmits light at a predetermined rate regardless of the polarization state. The reflected laser light reflected by the combining half mirror 33 enters the first light receiving unit 36 of the detector 38. The reflected laser light transmitted through the combining half mirror 33 is reflected by the mirror 34 and is incident on the second light receiving unit 37 of the detector 38.

  Next, the optical path of the reference light will be described. The P-wave reference laser light that has passed through the branching PBS 16 is reflected by the mirror 41 and the mirror 42 and enters the band-pass filter 43. The band pass filter 43 is a filter having a pass band around a wavelength of 1532 nm. The reference laser light that has passed through the bandpass filter 43 enters the mirror 44.

  The mirror 44 has two reflecting surfaces inclined with respect to each other. The reference laser light reflected by one reflecting surface of the mirror 44 enters the half mirror 45. The half mirror 45 reflects half of the incident reference laser light and transmits the other half. The half mirror 45 reflects or transmits light at a predetermined ratio regardless of the polarization state. The reference laser beam reflected by the half mirror 45 is collected by the lens 46 and enters the fiber 48. The fiber 48 is a constant polarization plane fiber.

  The reference laser light emitted from the fiber 48 is incident on the reference mirror 55. The reference mirror 55 is provided to make the laser Doppler vibrometer 1 differential. That is, the reference mirror 55 is arranged so that the reference laser beam is reflected in the same vector direction as the vibration direction of the measurement object 5 to be measured. Thereby, the vibration component of the main body 101 is canceled, and only the vibration component of the measurement object 5 can be detected. The reference mirror 55 is installed in the fixed part 56 by a clamp or the like, for example. The fixed portion 56 is a ground, a support, or a structure provided outside the automobile 4.

  In the optical system of the laser Doppler vibrometer 1, only the reference mirror 55 is not fixed to the main body portion 101, and the reference mirror 55 is directly installed on the fixed portion 56. Therefore, even if the main body 101 vibrates due to the vibration of the measurement environment, the reference mirror 55 does not vibrate. The vibration received by the laser Doppler vibrometer 1 itself can be canceled. Thereby, the influence of the vibration by the engine of the motor vehicle 4 or the vibration generated when the worker 6 moves can be canceled. As described above, the reference mirror 55 is provided to cancel a noise component due to vibration of the measurement environment.

  The reference laser light reflected by the reference mirror 55 enters the half mirror 45 through the fiber 48 and the lens 46. The reference laser light reflected by the half mirror 45 is incident on the other reflecting surface of the mirror 49. Then, the reference laser light is reflected by the other reflecting surface of the mirror 44 and enters the combining half mirror 33.

  The synthesizing half mirror 33 transmits part of the reference laser light and reflects the rest. The reference laser light transmitted through the combining half mirror 33 is incident on the first light receiving unit 36 of the detector 38. The reference laser beam reflected by the combining half mirror 33 is reflected by the mirror 34 and enters the second light receiving unit 37 of the detector 38. As described above, the reference laser light propagates through the optical system in the main body 101 and enters the detector 38.

  The synthesizing half mirror 33 is a synthesizing unit that synthesizes the reference laser beam (reference beam) and the reflected laser beam (signal beam). That is, the reference laser beam and the reflected laser beam are superimposed on each other by the synthesizing half mirror 33 and propagated coaxially. The synthesizing half mirror 33 generates synthesized light in which the reference laser beam and the reflected laser beam are superimposed. The combined light is detected by the detector 38. Note that the reference laser beam and the reflected laser beam have different frequencies due to Doppler shift and FM modulation.

  The first light receiving unit 36 and the second light receiving unit 37 photoelectrically convert the detection light into an electric signal. The first light receiving unit 36 and the second light receiving unit 37 have, for example, InGaAs avalanche photodiodes having sensitivity at a wavelength of 1532 nm. The first light receiving unit 36 and the second light receiving unit 37 are not limited to photodiodes, and may be photomultiplier tubes, for example. The detector 38 performs A / D conversion on the electrical signals output from the first light receiving unit 36 and the second light receiving unit 37, respectively. Thereby, the detector 38 outputs a detection signal corresponding to the light amount of the combined light including the reference laser light and the reflected laser light.

  A detection signal from the detector 38 is input to the demodulator 62. The demodulator 62 demodulates the detection signal according to the modulation frequency in the AOM 31. Therefore, the demodulator 62 FM-demodulates the detection signal at 80 MHz. The detection signal demodulated by the demodulator 62 is output to the processing device 63.

  The processing device 63 is an information processing device such as a laptop workstation or a notebook computer. The processing device 63 performs predetermined processing on the detection signal from the demodulator 62. By doing so, only the vibration component of the measuring object 5 can be extracted. The processing device 63 calculates vibration from the detection result of the detector 38. For example, the processing device 63 obtains the spectral distribution of the vibration component by performing Fourier transform or the like. Then, the processing device 63 extracts a beat signal using a frequency filter. Thereby, the vibration signal according to the vibration of the measuring object 5 can be obtained. And the processing apparatus 63 can calculate | require the damage and the deterioration degree of the measuring object 5 by analyzing a vibration component.

  In this embodiment, the combined light transmitted through the combining half mirror 33 is detected by the first light receiving unit 36, and the combined light reflected by the combining half mirror 33 is detected by the second light receiving unit 37. That is, the detector 38 detects the two combined lights from the combining half mirror 33, respectively. The combined light incident on the first light receiving unit 36 and the combined light incident on the second light receiving unit 37 are out of phase, but the phases can be made uniform by processing in the processing device 63. By doing so, it is possible to obtain a signal strength that is substantially doubled, and to perform measurement with higher accuracy.

  Further, the processing device 63 is connected to the controller 64. The controller 60 includes a galvano controller 65, a polygon driver 66, a piezo controller 67, and a servo motor controller 68. The galvano controller 65 controls the galvanometer mirror 25. That is, when the galvano controller 65 drives the galvanometer mirror 25, the irradiation laser light is scanned. The polygon driver 66 controls the polygon mirror 24. That is, the polygon driver 66 scans the irradiation laser light by driving the motor of the polygon mirror 24. The galvano controller 65 and the polygon driver 66 drive the galvano mirror 25 and the polygon mirror 24 in synchronization. By doing so, the irradiation laser light is two-dimensionally scanned. Thereby, vibration can be measured for a predetermined region of the measuring object 5.

  The servo motor controller 68 controls the servo motor 51. That is, when the servo motor controller 68 drives the servo motor 51, the reflective λ / 4 plate 21 and the convex mirror 22 move in the direction of arrow A. Thereby, the focal position can be adjusted.

  In the laser Doppler vibrometer 1 according to the present embodiment, the measurement distance is about 1 km and the NA is small. The measurement depth (depth of field) is increased to about 100 m. Once focused, it can be scanned at once and the measurement can be terminated.

  In addition, when the surface of the measurement object 5 is uneven or when a high-rise building or the like is measured from the ground, there is a possibility that it cannot be performed at some points due to the shift of the focal position. In this case, an XY scan can be performed before measurement, and a focus condition with a high signal intensity at each point can be set in the processing device 63 in advance. That is, an appropriate focal position can be obtained at each point. For example, the focal position can be set based on the detection result of the detector 38 or the camera 81. By doing so, the number of measurement points at which no signal can be detected can be reduced. Further, a retry function may be provided to measure again a point where a signal cannot be detected. It is also possible to perform focusing using an optical system.

  The piezo controller 67 controls the adaptive optical element 27. The piezo controller 67 drives a piezo actuator provided in the adaptive optical element 27. By providing the compensation optical element 27, the concave mirror 23 becomes a deformable mirror. The configuration of the compensation optical element 27 will be described later.

  As described above, the reflective λ / 4 plate 21 is used as a λ / 4 plate that converts linearly polarized light into circularly polarized light. By doing so, noise can be reduced as compared with the case where a transmission type λ / 4 plate is used. When the transmission type λ / 4 plate is used, the irradiation laser beam and the reflected laser beam change to the polarization state when the transmission type λ / 4 plate passes through the transmission type λ / 4 plate. Therefore, the S-polarized component contained in the reflected laser light increases and optical noise is generated. On the other hand, in the present embodiment, since the reflection type λ / 4 plate 21 is used, the generation of optical noise can be prevented. Therefore, even when the measurement distance becomes long, it can be measured accurately.

  Further, since optical noise can be reduced, the laser light output need not be increased. Therefore, the safety class of the laser can be lowered. A small infrared laser light source 11 can be used, and the apparatus can be miniaturized. Furthermore, since the output of the infrared laser light source 11 is low, power consumption can be reduced.

  Further, in the present embodiment, the convex mirror 22 and the concave mirror 23 are arranged after the branching PBS 16 for separating the irradiation laser light into the S wave and the P wave, and the irradiation laser light is irradiated. The irradiation laser beam branched from the reference laser beam by the branching PBS 16 is condensed by the reflective optical element. By so doing, it is possible to reduce the change in polarization state that occurs when passing through the transmissive optical element. For example, it is possible to reduce changes in the polarization state caused by passing through an optical element such as a lens. Therefore, generation of optical noise can be reduced, and accurate measurement can be performed even when the measurement distance is long.

  According to the present embodiment, it is possible to measure the measurement object 5 at a distance of 1 km. Furthermore, if the conditions such as the atmosphere are met, it is possible to measure the measurement object 5 at a distance of 2 to 3 km. Therefore, even if the measurement object 5 is in a dangerous environment, the worker 6 can work in a safe environment. It can also be applied to seismic diagnosis of buildings such as hospitals and schools.

  Furthermore, the servo motor 51 moves the convex mirror 22 and the reflective λ / 4 plate 21 together, so that the focal position can be easily adjusted. By doing so, the condensing point of the irradiation laser light can be adjusted to the surface of the measuring object 5. Therefore, measurement can be performed easily.

  Next, the optical path of the visible laser light source 71 will be described. The visible laser light source 71 emits laser light having a wavelength of 532 nm, for example. Of course, the wavelength of the visible laser light source 71 is not particularly limited. In FIG. 2, the optical path of the visible laser light is arranged one step below the optical path of the infrared laser light. That is, the positions of the visible laser light source 71 and the infrared laser light source 11 are different in the direction perpendicular to the paper surface. Then, it is made coaxial with the infrared laser beam by a combining unit 79 described later.

  Visible laser light from the visible laser light source 71 becomes guide light for alignment. The visible laser light passes through the fiber 72 and enters the lens 73. The lens 73 makes visible laser light a parallel light beam. The visible laser beam converted into a parallel light beam by the lens 73 passes through the isolator 74 and enters the half mirror 75. The isolator 74 prevents the return light from entering the visible laser light source 71.

  The half mirrors 75 and 76 transmit part of the visible laser light and reflect the rest. The visible laser beam that has passed through the half mirror 75 enters the half mirror 76. The visible laser light that has passed through the half mirror 76 is reflected by the mirror 77 and the mirror 78 and enters the combining unit 79. The combining unit 79 includes a plurality of optical elements such as mirrors, for example, and combines the visible laser beam and the irradiation laser beam so as to be coaxial. For example, the combining unit 79 includes a perforated mirror and the like, and can make visible laser light coaxial with infrared laser light. Then, the visible laser beam from the synthesis unit 79 is irradiated on the convex mirror 22 along the same axis as the irradiation laser beam. Therefore, it is incident on the measuring object 5 in the same manner as the irradiation laser beam.

  The visible laser beam reflected by the measurement object 5 propagates through the same optical path as the reflected laser beam. That is, the visible laser beam reflected by the measurement object 5 is incident on the PBS 17 through the galvano mirror 25, the polygon mirror 24, the concave mirror 23, the convex mirror 22, and the reflective λ / 4 plate 21. The PBS 17 reflects a part of the visible laser light in the direction of the branching PBS 16. The visible laser light reflected by the PBS 17 passes through the branching PBS 16 and the half mirror 76 and enters the imaging lens 80. The imaging lens 80 collects visible laser light on the camera 81. That is, the imaging lens 80 forms an image of the measuring object 5 on the camera 81.

  The camera 81 is a two-dimensional array photodetector such as a CMOS (Complementary Metal Oxide Semiconductor) camera or a CCD (Charge Coupled Device) camera. The camera 81 images the measurement object 5 illuminated with a visible light laser. An image captured by the camera 81 is output to the processing device 63 and displayed on the monitor of the processing device 63. Thereby, the operator 6 can confirm where in the measuring object 5 coincides with the optical axis. That is, the operator 6 can visually recognize the irradiation positions of the irradiation laser light and the visible laser light on the measurement object 5 by the image acquired by the camera 81. The position of the irradiation laser beam can be adjusted easily and appropriately. By aligning the optical system while the operator 6 looks at the irradiation position of the visible laser beam, the irradiation laser beam can be irradiated to a desired position of the measurement object 5. Therefore, the optical system can be easily adjusted.

  In this way, the infrared irradiation laser beam and the visible laser beam are combined so as to be coaxial, and the measurement object 5 is irradiated. In this way, alignment of infrared irradiation laser light can be easily performed.

  Next, the optical path of the laser range finder 91 will be described. The laser beam from the laser range finder 91 is reflected by the mirror 92 and enters the half mirror 75. The laser light reflected by the half mirror 75 propagates through the same optical path as the visible laser light. The laser light from the laser range finder 91 is coaxial with the laser light from the visible laser light source 71 and enters the measurement object 5. Then, the return light from the measurement object 5 enters the laser range finder 91. Thereby, the approximate distance to the measurement object 5 and the irradiation position can be measured.

The mirror used in the laser Doppler vibrometer 1 is preferably a mirror having a high reflectance at a wavelength of 300 nm to 2000 nm, for example, an Al mirror overcoated with MgF ₂ or a dielectric multilayer mirror.

  DC power from the battery 2 shown in FIG. 1 is supplied to electrical devices such as the detector 38, the demodulator 62, the AOM driver 61, the processing device 63, and the controller 64. By measuring without using an AC power supply, the influence of AC noise can be reduced. Thereby, a measurement distance can be lengthened.

  The wavefront sensor 93 includes, for example, a Shack-Hartmann sensor or a curvature sensor. The Shack-Hartmann sensor measures image shift by a fine lens array. The curvature sensor captures changes in light intensity by moving the sensor body, and captures the state of the wavefront due to wave interference. A sensor signal from the wavefront sensor 93 is input to the processing device 63.

  The processing device 63 includes a phase control computer that performs phase control calculation based on the sensor signal. Then, the processing device 63 generates a control signal for controlling the concave mirror 23 that is a deformable mirror. The processing device 63 outputs a control signal to the piezo controller 67. Then, the piezo controller 67 controls the adaptive optical element 27.

  The wavefront sensor 83 is not particularly limited. For example, a telephoto lens and a CMOS camera may be used for the wavefront sensor 93. And the processing apparatus 63. Pattern matching between the image acquired by the CMOS camera of the wavefront sensor 93 and the image acquired by the camera 81 may be performed. The processing device 63 may generate a control signal based on the result of pattern matching.

  Next, the configurations of the compensation optical element 27 and the concave mirror 23 will be described with reference to FIGS. 3 and 4. FIG. 3 is a front view of the concave mirror 23, and FIG. 4 is a side sectional view of the concave mirror 23 and the compensation optical element 27. The compensation optical element 27 is provided to compensate the wavefront of the reflected laser light.

  As shown in FIG. 3, the concave mirror 23 is divided into a plurality of regions 23b by slits 23a. Here, it is divided into four concentric circles and eight radially. That is, the concave mirror 23 is divided into 32 regions 23b.

  The compensation optical element 27 has a plurality of piezo actuators 27a. As shown in FIG. 4, the piezo actuator 27 a is disposed on the back surface of the concave mirror 23. A piezo actuator 27 a is provided for each region 23 b of the concave mirror 23. Therefore, the compensation optical element 27 has 32 piezo actuators 27a.

  The plurality of piezo actuators 27 a are connected to the piezo controller 67. The piezo controller 67 drives a plurality of piezo actuators 27a independently. In other words, the piezo actuator 27a expands and contracts back and forth by the drive signal from the piezo controller 67. By doing so, the region 23b of the concave mirror 23 moves in the direction of the arrow in FIG.

  Thus, the piezoelectric actuator 27a is provided in the area | region 23b of the concave mirror 23, respectively. Accordingly, the position of the reflecting surface of the concave mirror 23 can be adjusted by independently driving the piezo actuator 27a. Thereby, the distortion of the wavefront of the reflected laser light can be corrected. Therefore, optical aberration, that is, noise can be reduced.

  The piezo controller 67 controls the piezo actuator 27 a based on the detection result of the wavefront sensor 93. By so doing, wavefront distortion due to air fluctuations and the like can be corrected. Therefore, even when the measurement distance becomes long, it can be measured more accurately.

  In addition, when the 1st light-receiving part 36 and the 2nd light-receiving part 37 have a detection sensitivity in wavelength 532nm, visible laser beam will turn into white noise. Therefore, it is desirable that the first light receiving unit 36 and the second light receiving unit 37 be photodiodes having no detection sensitivity at a wavelength of 532 nm. Alternatively, one or more filters such as a band-pass filter and a long-pass filter that shield light of wavelength 532 may be disposed in front of the first light-receiving unit 36 and the second light-receiving unit 37.

  As mentioned above, although embodiment of this invention was described, this invention contains the appropriate deformation | transformation which does not impair the objective and advantage, Furthermore, it does not receive the restriction | limiting by said embodiment.

DESCRIPTION OF SYMBOLS 1 Laser Doppler vibrometer 2 Battery 3 Gas cylinder 4 Automobile 5 Measurement object 6 Worker 101 Main part 11 Infrared laser light source 12 Fiber 13 Lens 14 Isolator 15 Gran Thompson prism 16 Branching PBS
17 PBS
18 Wavelength converting means 21 Reflective λ / 4 plate 22 Convex mirror 23 Concave mirror 23a Slit 24 Polygon mirror 25 Galvano mirror 27 Compensating optical element 27a Piezo actuator 28 Window 31 AOM
32 mirror 33 half mirror for synthesis 34 mirror 36 first light receiving unit 37 second light receiving unit 38 detector 41 mirror 42 mirror 43 band pass filter 44 mirror 45 half mirror 46 lens 48 fiber 49 mirror 55 reference mirror 56 reference mirror 50 linear drive Device 51 Servo motor 52 Linear guide 53 Base 61 AOM driver 62 Demodulator 63 Processing device 64 Controller 65 Galvano controller 66 Polygon driver 67 Piezo controller 68 Servo motor controller 71 Visible laser light source 72 Fiber 73 Lens 74 Isolator 75 Half mirror 76 Half mirror 77 Mirror 78 Mirror 79 Synthesizer 80 Imaging lens 81 Camera 91 Laser range finder 92 Mirror 93 Wavefront sensor

Claims (8)

A laser light source;
A first polarization beam splitter that generates a reference laser beam and an irradiation laser beam irradiated to a measurement object by branching the laser beam from the laser light source;
A second polarization beam splitter that receives the irradiation laser light and receives the reflected laser light reflected by the measurement object;
A reflective λ / 4 plate that is disposed between the second polarizing beam splitter and the measurement object and reflects the irradiation laser light and the reflected laser light;
A frequency shifter for shifting the frequency of the reflected laser light from the second polarizing beam splitter;
Combining the reflected laser light frequency-shifted by the frequency shifter with the reference laser light to generate combined light;
A detector for detecting the combined light;
A laser Doppler measurement device comprising: a processing device that calculates vibration of a measurement object based on an output signal from the detector. A convex mirror on which the irradiation laser light from the second polarizing beam splitter is incident;
The laser Doppler measurement apparatus according to claim 1, further comprising: a concave mirror that reflects the irradiation laser light reflected by the convex mirror and focuses the light on the measurement target.   The laser Doppler measurement apparatus according to claim 2, further comprising a driving unit that moves the convex mirror together with the reflective λ / 4 plate to adjust a focal position of the irradiation laser light.   The laser Doppler measurement apparatus according to claim 2, wherein an adaptive optical element is provided on the concave mirror.   The laser Doppler measurement apparatus according to claim 1, wherein the irradiation laser light has a wavelength of 1532 nm.   The laser Doppler measurement apparatus according to claim 5, further comprising a visible laser light source that emits a visible laser beam that irradiates the measurement object coaxially with an infrared laser beam.   The laser Doppler measurement apparatus according to claim 1, further comprising an optical scanner that includes a reflection surface that reflects the laser light, and that scans the laser light by changing an angle of the reflection surface. . A laser light source emitting laser light;
A step of generating a reference laser beam and an irradiation laser beam irradiated on the measurement object by the first polarization beam splitter branching the laser beam;
Incident the irradiated laser light on a second polarizing beam splitter;
Reflecting the irradiated laser light from the second polarizing beam splitter by a reflective λ / 4 plate;
Irradiating the object to be measured with the irradiation laser beam reflected by the reflection type λ / 4;
Reflecting the reflected laser beam reflected by the measurement object by the reflection type λ / 4;
Making the reflected laser light reflected by the reflective λ / 4 plate incident on the second polarizing beam splitter;
Shifting the frequency of the reflected laser light from the second polarizing beam splitter;
A combining step of combining the reflected laser beam having the frequency shifted with the reference laser beam to generate a combined beam;
Detecting the combined light;
Calculating a vibration of the measurement object based on the detection result of the combined light, and a laser Doppler measurement method.

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