A concave mirror reflection focusing type laser vibrometer calibration device and method

Abstract

A calibration device and method for a concave mirror reflection focusing type laser vibrometer disclosed by the present invention belong to the technical field of optoelectronic measurement. The device of the present invention includes a laser vibrometer, a first λ / 2 wave plate, a second λ / 2 wave plate, a third λ / 2 wave plate, a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, a first concave mirror, a second concave mirror, a plane mirror, a first acousto-optic modulator, a second acousto-optic modulator, an FM signal source, a first sine signal source, and a second sine signal source. The present invention uses an acousto-optic modulator for optical frequency modulation excitation, and uses the spherical concave mirror focusing reflection method to solve the problems of beam divergence and fluttering movement generated by the acousto-optic modulator during the optical frequency modulation process. A sine waveform for simulating vibration is generated in an optical frequency modulation manner to excite a laser measurement signal, so as to provide an excitation source for the performance evaluation of the laser vibrometer and realize the calibration of the laser vibrometer. The present invention has a faster response time, a wider frequency range, and a larger amplitude range.

Description

Technical Field

[0001] The present invention relates to a calibration device and method for a concave mirror reflection focusing type laser vibrometer, belonging to the technical field of optoelectronic measurement. Background Art

[0002] A laser vibrometer is a general and fundamental vibration and shock measurement instrument, which is a measurement instrument with high precision, non-contact, and no additional interference and influence on the measured object. Its metrological calibration and performance evaluation have always been difficult problems in the industry. The main reasons are as follows: 1) Its excitation is the amount of motion (displacement, velocity, acceleration), and the measurement principle used is based on the laser Doppler effect. It is necessary to perceive physical motion through the change of optical frequency, and the output is given in the form of electrical signal data, involving different aspects such as mechanical motion, optical frequency control, and electronic measurement. 2) Since the frequency range and accuracy of optoelectronic measurement are much higher than those of mechanical motion quantity values, there has always been a lack of a suitable excitation source for its metrological calibration and performance evaluation, and it is very difficult to find a device and equipment that meet the requirements. 3) Usually, its metrological calibration is carried out by exciting with a "standard vibration table" and measuring the quantity value with a "standard laser vibrometer" to calibrate other laser vibrometers. Since the vibration table is a physical motion device of an electromechanical structure, limited by physical principles, mechanical principles, etc., and limitations such as materials and mechanical processing capabilities, compared with this optoelectronic measurement instrument of a laser vibrometer, its stability is not easy to reach a very high level, the frequency band is narrow, and the amplitude can reach a relatively large quantity value at low frequencies. In the case of high frequencies, the amplitude can only achieve a very small quantity value, and the accuracy is also low, and it is not easy to meet the technical requirements for metrological traceability of laser vibration measurement. Although a standard laser vibrometer is used for metrological calibration, the uncertainty caused by the characteristics of the vibration table and the limitations caused by its amplitude and frequency range are still the main problems existing in the metrological calibration of laser vibrometers. 4) On the other hand, when using a standard laser vibrometer to perform metrological traceability on other laser vibrometers itself, there is still a logical problem that the metrological calibration problem of the standard laser vibrometer itself still cannot be solved. Summary of the Invention

[0003] Aiming at the main problems existing in the metrological calibration and performance evaluation of laser vibrometers, that is, the technical parameters limited by mechanical movements such as vibration tables cannot fully cover the range of the vibrometer and the stability is inferior to that of the vibrometer, and the problem that the metrological traceability of the standard laser vibrometer cannot be fully solved, the main purpose of the present invention is to provide a concave mirror reflection focusing type laser vibrometer calibration device and method, which uses an acousto-optic modulator (AOM) for optical frequency modulation excitation, and uses the spherical concave mirror focusing reflection method to solve the problems of beam divergence and fluttering movement generated by the acousto-optic modulator during the optical frequency modulation process, generates a sine waveform excitation of the laser measurement signal by optical frequency modulation to simulate vibration, so as to solve the excitation source problem for the evaluation of the characteristics of the laser vibrometer, and further realize the calibration of the concave mirror reflection focusing type laser vibrometer.

[0004] The purpose of the present invention is achieved by the following technical solutions:

[0005] The present invention is achieved by the following technical solutions.

[0006] A concave mirror reflection focusing type laser vibrometer calibration device disclosed by the present invention includes a laser vibrometer, a first λ / 2 wave plate, a second λ / 2 wave plate, a third λ / 2 wave plate, a first polarization beam splitter, a second polarization beam splitter, a third polarization beam splitter, a first concave mirror, a second concave mirror, a plane mirror, a first acousto-optic modulator, a second acousto-optic modulator, an FM signal source, a first sine signal source, and a second sine signal source.

[0007] The laser generated by the laser vibrometer passes through the first polarization beam splitter, the second polarization beam splitter, and the first λ / 2 wave plate and reaches the first acousto-optic modulator. The first sine signal source generates the required sine waveform modulation signal to control the first acousto-optic modulator, shift the frequency of the laser signal coming from the direction of the first λ / 2 wave plate, and generate the -1st order diffracted light, which is then reflected and focused by the first concave mirror, returns to the first acousto-optic modulator to continue frequency shifting, then passes through the first λ / 2 wave plate, is reflected by the second polarization beam splitter, and the reflection of the third polarization beam splitter, passes through the third λ / 2 wave plate, and reaches the second acousto-optic modulator. The second sine signal source generates the required sine waveform modulation signal to frequency modulate the FM signal source to generate the modulated FM signal. By controlling the second acousto-optic modulator, frequency shift modulation is performed on the laser transmitted by the third λ / 2 wave plate to generate the +1st order diffracted laser, which is reflected and focused by the second concave mirror, returns to the second acousto-optic modulator for frequency shift modulation again, passes through the third λ / 2 wave plate and the third polarization beam splitter in sequence, is reflected by the plane mirror, passes through the second λ / 2 wave plate, is reflected by the first polarization beam splitter, and returns to the laser vibrometer to be calibrated for measurement and processing, realizing the simulation process of vibrating the laser vibrometer with the sine waveform generated by the second sine signal source.

[0008] The excitation response characteristics of the laser vibrometer are obtained from the comparison between the waveform results measured by the laser vibrometer and the second sine signal source, and then the performance evaluation and calibration of the concave mirror reflection focusing type laser vibrometer are realized.

[0009] Preferably, the first acousto-optic modulator is used for frequency shifting, and the first concave mirror is used for reflection and focusing. The second acousto-optic modulator is used for laser frequency modulation, and the second concave mirror is used for reflection and focusing to overcome the problem of the spot of the diffraction-modulated laser fluttering and moving.

[0010] Preferably, both the first concave mirror and the second concave mirror used are spherical mirrors. The first acousto-optic modulator is placed at the center of the sphere of the first concave mirror, and the second acousto-optic modulator is placed at the center of the sphere of the second concave mirror.

[0011] Preferably, for the first acousto-optic modulator and the second acousto-optic modulator used, their frequency shifting and modulation can not only work on the ±1st diffraction order respectively, but also work on other arbitrary diffraction orders such as the ±2nd diffraction order and the ±3rd diffraction order.

[0012] Preferably, the measurement device completely uses the frequency-stabilized laser emitted by the laser vibrometer to be measured and does not require its own laser light source. Therefore, the cost can be reduced, and the uncertainty caused by the inconsistency between the laser light source parameters of the standard device and the laser parameters to be calibrated can be avoided.

[0013] A calibration method for a concave mirror reflection focusing type laser vibrometer disclosed by the present invention is realized based on the above-mentioned calibration device for a concave mirror reflection focusing type laser vibrometer.

[0014] The acousto-optic modulator is used for frequency shifting to obtain the waveform of the laser frequency modulation signal of the optical frequency modulator. Then, in the control mode of the frequency modulation signal modulated by the acousto-optic modulator in a sine waveform, the optical frequency modulation signal is made to maintain the characteristic of the median frequency unchanged and returned to the laser vibrometer for measurement processing to obtain its response waveform during the sine waveform movement.

[0015] Aiming at the problems of the laser beam deviation and divergence caused by the diffraction effect during the modulation process of the acousto-optic modulator, and the problem of the laser beam fluttering and moving, a concave mirror with a spherical surface feature is used for reflection and convergence, and the acousto-optic modulator is placed at the center of the sphere of the concave mirror, so that the scattered and drifting light in any direction is finally reflected and converged to the center of the sphere to solve the problem of the laser beam fluttering and moving and obtain a stable and reliable returned laser.

[0016] Using an electrical signal to control an optical signal to generate a laser Doppler signal with a sinusoidal waveform motion characteristic, replacing the physical mechanical motion with optical frequency control variation to generate the Doppler frequency shift method, directly generating an optical frequency modulation signal with a moving Doppler characteristic, thereby avoiding the difficulty of generating a high-quality sinusoidal waveform motion signal by mechanical motion. Thus, calibrating or evaluating the response characteristics of the sinusoidal waveform motion of a laser vibrometer. Compared with excitations such as a vibration table, this embodiment has a faster response time, a wider frequency range, and a larger amplitude range.

[0017] In this embodiment, the magnitude of the linear motion signal (linear motion velocity, linear motion acceleration) is traced back to the frequency magnitude through frequency modulation and demodulation techniques. Therefore, in principle, it has higher measurement accuracy and stability than mechanical motion excitation. Because the frequency magnitude is a physical quantity with the highest measurement accuracy that people can achieve in today's metrology industry, far higher than any other physical quantity.

[0018] Beneficial effects:

[0019] 1. A concave mirror reflection focusing type laser vibrometer calibration device disclosed by the present invention uses an electrical signal to control an optical signal to generate a laser Doppler signal with a sinusoidal waveform motion characteristic, replacing the physical mechanical motion with optical frequency control variation to generate the Doppler frequency shift method, directly generating an optical frequency modulation signal with a moving Doppler characteristic, thereby avoiding the difficulty of generating a high-quality sinusoidal waveform motion signal by mechanical motion. Thus, calibrating or evaluating the response characteristics of the sinusoidal waveform motion of a laser vibrometer. Compared with excitations such as a vibration table, the present invention has a faster response time, a wider frequency range, and a larger amplitude range.

[0020] 2. A concave mirror reflection focusing type laser vibrometer calibration device disclosed by the present invention uses an acousto-optic modulator for frequency shifting to obtain the laser frequency modulation signal waveform of the acousto-optic modulator, and then uses the acousto-optic modulator in a frequency modulation signal control mode modulated by a sinusoidal waveform, so that the optical frequency modulation signal maintains the characteristic of constant median frequency and returns to the laser vibrometer for measurement processing to obtain its response waveform during sinusoidal waveform motion.

[0021] 3. A concave mirror reflection focusing type laser vibrometer calibration device disclosed by the present invention aims at the problems of laser beam offset divergence and laser beam fluttering movement during the modulation process of the acousto-optic modulator. The present invention uses a concave mirror with a spherical surface characteristic for reflection and convergence, places the acousto-optic modulator at the center of the concave mirror sphere, so that the scattered and drifting light in any direction is finally reflected and converged to the center of the sphere to solve this problem and obtain a stable and reliable return laser.

[0022] 4. A calibration device for a concave mirror reflection focusing type laser vibrometer disclosed by the present invention traces the magnitude of a linear motion signal (linear motion speed, linear motion acceleration) to a frequency magnitude through frequency modulation and demodulation techniques. Therefore, in principle, it has higher measurement accuracy and stability than mechanical motion excitation. Since the frequency magnitude is a physical quantity that can achieve the highest measurement accuracy in today's metrology industry, far higher than any other physical quantity. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 FIG. is a schematic structural diagram of a calibration device for a concave mirror reflection focusing type laser vibrometer disclosed by the present invention.

[0024] Wherein: 1 - laser vibrometer, 2 - first polarization beam splitter, 3 - second polarization beam splitter, 4 - first λ / 2 wave plate, 5 - first acousto-optic modulator, 6 - first concave mirror, 7 - first sine signal source, 8 - second λ / 2 wave plate, 9 - plane mirror, 10 - third polarization beam splitter, 11 - third λ / 2 wave plate, 12 - second acousto-optic modulator, 13 - second concave mirror, 14 - FM signal source, 15 - second sine signal source. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In order to better illustrate the purpose and advantages of the present invention, the following further describes the content of the invention with reference to the drawings and examples.

[0026] Embodiment 1:

[0027] As Figure 1 shown, a calibration device for a concave mirror reflection focusing type laser vibrometer disclosed in this embodiment includes a laser vibrometer 1, a first λ / 2 wave plate 4, a second λ / 2 wave plate 8, a third λ / 2 wave plate 11, a first polarization beam splitter 2, a second polarization beam splitter 3, a third polarization beam splitter 10, a first concave mirror 6, a second concave mirror 13, a plane mirror 9, a first acousto-optic modulator 5, a second acousto-optic modulator 12, an FM signal source 14, a first sine signal source 7, a second sine signal source 15, etc.

[0028] The laser generated by the laser vibrometer 1 passes through the first polarization beam splitter 2, the second polarization beam splitter 3, and the first λ / 2 wave plate 4, and reaches the first acousto-optic modulator 5. The first sine signal source 7 generates the required sine waveform modulation signal to control the first acousto-optic modulator 5, shift the frequency of the laser signal coming from the direction of the first λ / 2 wave plate 4, and generate the -1st order diffracted light, which is then reflected and focused by the first concave mirror 6, returns to the first acousto-optic modulator 5 to continue frequency shifting, then passes through the first λ / 2 wave plate 4, is reflected by the second polarization beam splitter 3, and is reflected by the third polarization beam splitter 10, passes through the third λ / 2 wave plate 11, and reaches the second acousto-optic modulator 12. The second sine signal source 15 generates the required sine waveform modulation signal to frequency modulate the FM signal source 14 to generate the modulated FM signal. By controlling the second acousto-optic modulator 12, the laser coming from the third λ / 2 wave plate 11 is frequency shift modulated to generate the +1st order diffracted laser, which is reflected and focused by the second concave mirror 13, returns to the second acousto-optic modulator 12 for frequency shift modulation again, passes through the third λ / 2 wave plate 11 and the third polarization beam splitter 10 in sequence, is reflected by the plane mirror 9, passes through the second λ / 2 wave plate 8, is reflected by the first polarization beam splitter 2, and returns to the laser vibrometer 1 to be calibrated for measurement and processing, completing the simulation process of vibrating and exciting the laser vibrometer 1 with the sine waveform generated by the second sine signal source 15.

[0029] From the comparison between the waveform result measured by the laser vibrometer 1 and the second sine signal source 15, the excitation response characteristics of the laser vibrometer 1 can be obtained, and further the performance evaluation and calibration of the concave mirror reflection focusing type laser vibrometer can be realized.

[0030] In this embodiment, an acousto-optic modulator is used for frequency shifting to obtain the laser frequency modulation signal waveform of the optical frequency modulator, and then the acousto-optic modulator is used to control the frequency modulation signal in the way of sine waveform modulation, so that the optical frequency modulation signal maintains the characteristic of unchanged median frequency and returns to the laser vibrometer for measurement and processing to obtain its response waveform during sine waveform motion.

[0031] In this embodiment, aiming at the problems of laser beam offset divergence and laser beam fluttering during the modulation process of the acousto-optic modulator due to diffraction effects, a concave mirror with spherical characteristics is used for reflection and convergence. The acousto-optic modulator is placed at the center of the concave mirror sphere, so that the scattered and drifting light in any direction is finally reflected and converged to the center of the sphere to solve this problem and obtain a stable and reliable return laser.

[0032] In this embodiment, an electrical signal is used to control an optical signal to generate a laser Doppler signal with a sinusoidal waveform motion characteristic. By using optical frequency control variation to replace the physical mechanical motion to generate the Doppler frequency shift method, an optical frequency modulation signal with a motion Doppler characteristic is directly generated, thereby avoiding the difficulty of generating a high-quality sinusoidal waveform motion signal by mechanical motion. Thus, the response characteristics of the sinusoidal waveform motion of a laser vibrometer are measured and calibrated or evaluated. Compared with excitations such as vibration tables, this embodiment has a faster response time, a wider frequency range, and a larger amplitude range.

[0033] In this embodiment, the magnitude values of the linear motion signals (linear motion velocity, linear motion acceleration) are traced back to the frequency magnitude through frequency modulation and demodulation techniques. Therefore, in principle, it has higher measurement accuracy and stability than mechanical motion excitation. Because the frequency magnitude is a physical quantity with the highest measurement accuracy that people can achieve in today's metrology industry, far higher than any other physical quantity.

[0034] The above specific description further details the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above is only a specific embodiment of the present invention and is not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A calibration device for a concave mirror reflection focusing type laser vibrometer, characterized in that: it includes a laser vibrometer (1), a first λ / 2 wave plate (4), a second λ / 2 wave plate (8), a third λ / 2 wave plate (11), a first polarization beam splitter (2), a second polarization beam splitter (3), a third polarization beam splitter (10), a first concave mirror (6), a second concave mirror (13), a plane mirror (9), a first acousto-optic modulator (5), a second acousto-optic modulator (12), an FM signal source (14), a first sine signal source (7), and a second sine signal source (15); The laser generated by the laser vibrometer (1) passes through the first polarization beam splitter (2), the second polarization beam splitter (3), and the first λ / 2 wave plate (4) and reaches the first acousto-optic modulator (5). The first sine signal source (7) generates the required sine waveform modulation signal to control the first acousto-optic modulator (5) to shift the frequency of the laser signal coming from the direction of the first λ / 2 wave plate and generate -1 order diffracted light, which is then reflected and focused by the first concave mirror (6), returns to the first acousto-optic modulator (5) to continue frequency shifting, then passes through the first λ / 2 wave plate (4), is reflected by the second polarization beam splitter (3), and is reflected by the third polarization beam splitter (10), passes through the third λ / 2 wave plate (11), and reaches the second acousto-optic modulator (12). The second sine signal source (15) generates the required sine waveform modulation signal to frequency modulate the FM signal source (14) to generate a modulated FM signal. By controlling the second acousto-optic modulator (12), the laser coming from the third λ / 2 wave plate is frequency shift modulated to generate +1 order diffracted laser, which is reflected and focused by the second concave mirror (13), returns to the second acousto-optic modulator (12) for frequency shift modulation again, passes through the third λ / 2 wave plate (11) and the third polarization beam splitter (10) in sequence, is reflected by the plane mirror (9), passes through the second λ / 2 wave plate (8), is reflected by the first polarization beam splitter (2), and returns to the laser vibrometer (1) to be calibrated for measurement and processing, realizing the simulation process of vibrating the laser vibrometer (1) with the sine waveform generated by the second sine signal source (15); From the comparison between the waveform result measured by the laser vibrometer (1) and the second sine signal source (15), the excitation response characteristics of the laser vibrometer (1) are obtained, and further the performance evaluation and calibration of the concave mirror reflection focusing type laser vibrometer are realized.

2. A calibration device for a concave mirror reflection focusing type laser vibrometer according to claim 1, characterized in that: an electrical signal is used to control an optical signal to generate a laser Doppler signal with a sine waveform motion characteristic, and the Doppler frequency shift mode is generated by using the optical frequency control change to replace the physical mechanical motion, directly generating an optical frequency modulation signal with a moving Doppler characteristic, thereby generating a high-quality sine waveform motion signal.

3. A calibration device for a concave mirror reflection focusing type laser vibrometer according to claim 2, characterized in that: Use an acousto-optic modulator for frequency shifting to obtain the laser frequency modulation signal waveform of the optical frequency modulator. Then, use the acousto-optic modulator to control the frequency modulation signal modulated in a sine waveform, so that the optical frequency modulation signal returns to the laser vibrometer for measurement processing while maintaining the characteristic of the median frequency unchanged, and obtain its response waveform to the sine waveform motion.

4. A concave mirror reflection focusing type laser vibrometer calibration device as described in claim 3, characterized in that: Use a concave mirror with a spherical surface feature for reflection and convergence. Place the acousto-optic modulator at the center of the sphere of the concave mirror, so that the scattered and drifting light in any direction is reflected and converged to the center of the sphere to obtain a stable and reliable return laser.

5. A concave mirror reflection focusing type laser vibrometer calibration device as described in claim 1, characterized in that: Use the first acousto-optic modulator (5) for frequency shifting, reflect and focus with the first concave mirror (6), use the second acousto-optic modulator (12) for laser frequency modulation, and reflect and focus with the second concave mirror (13) to overcome the problem of the laser spot fluttering and moving due to diffraction modulation.

6. A concave mirror reflection focusing type laser vibrometer calibration device as described in claim 1, characterized in that: The first concave mirror (6) and the second concave mirror (13) used are both spherical mirrors. The first acousto-optic modulator (5) is placed at the center of the sphere of the first concave mirror (6), and the second acousto-optic modulator (12) is placed at the center of the sphere of the second concave mirror (13).

7. A concave mirror reflection focusing type laser vibrometer calibration device as described in claim 1, characterized in that: For the first acousto-optic modulator (5) and the second acousto-optic modulator (12) used, their frequency shifting and modulation can not only work on the ±1 diffraction orders respectively, but also work on other arbitrary diffraction orders such as ±2 diffraction orders and ±3 diffraction orders.

8. A concave mirror reflection focusing type laser vibrometer calibration device as described in claim 1, characterized in that: The measurement device completely uses the frequency-stabilized laser emitted by the laser vibrometer to be measured and does not require its own laser light source. Therefore, it can reduce costs and avoid the uncertainty caused by the inconsistency between the laser light source parameters of the standard device and the laser parameters to be calibrated.

9. A concave mirror reflection focusing type laser vibrometer calibration method, implemented based on a concave mirror reflection focusing type laser vibrometer calibration device as described in claim 1, characterized in that: Use an acousto-optic modulator for frequency shifting to obtain the laser frequency modulation signal waveform of the optical frequency modulator. Then, use the acousto-optic modulator to control the frequency modulation signal modulated in a sine waveform, so that the optical frequency modulation signal returns to the laser vibrometer for measurement processing while maintaining the characteristic of the median frequency unchanged, and obtain its response waveform to the sine waveform motion; Aiming at the problems of the divergence and deviation of the laser beam caused by the diffraction effect during the modulation process of the acousto-optic modulator, as well as the fluttering movement of the laser beam, a concave mirror with a spherical feature is used for reflection and convergence. The acousto-optic modulator is placed at the center of the sphere of the concave mirror, so that the scattered and drifting light in any direction is finally reflected and converged to the center of the sphere, to solve the problem of the fluttering movement of the laser beam and obtain a stable and reliable return laser; An electrical signal is used to control the optical signal to generate a laser Doppler signal with the motion characteristics of a sine wave. By using the optical frequency control variation to replace the physical mechanical motion to generate the Doppler frequency shift method, an optical frequency modulation signal with the motion Doppler characteristics is directly generated; The linear motion signal quantity is traced back to the frequency quantity through frequency modulation and demodulation techniques to realize the calibration of the laser vibrometer.

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