A laser vibration measuring device suitable for 0.1 mHz~10 kHz

Abstract

The application provides a laser vibration measuring device suitable for 0.1mHz-10kHz, which comprises a laser light source, a first polarization beam splitter prism, a second polarization beam splitter prism, a quarter-wave plate, a beam splitter, a first mirror, a second mirror, a frequency modulation device, a charge coupled device camera and a photoelectric detector arranged along an optical path in sequence. The laser vibration measuring device suitable for 0.1mHz-10kHz of the application uses a high-precision charge coupled device camera to measure the vibration parameters of a low-frequency vibrating object by measuring the interference fringes of light and dark, uses a photoelectric detector to measure the Doppler frequency shift to obtain the vibration parameters of a high-frequency vibrating object, and no matter whether the obtained vibration parameters are displacement or velocity, the vibration frequency can be converted through a mathematical relationship to realize vibration measurement, can be applied to the vibration measurement of most vibrating objects under the premise of ensuring good measurement accuracy, and thus the range of vibration measurement is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of laser vibration measurement technology, specifically relating to a laser vibration measurement device suitable for 0.1mHz to 10kHz. Background Technology

[0002] Laser technology emerged in the 1960s and is one of the major inventions of the 20th century. Due to its characteristics such as good directionality, high brightness and good monochromaticity, lasers have developed rapidly since their inception. By penetrating existing mature disciplines, many emerging technology fields related to lasers have been created.

[0003] Vibration testing is a crucial method for measuring product quality in manufacturing, and product quality plays a vital role in generating economic benefits and increasing GDP. In the manufacturing industry, most vibrations can be detrimental. For example, vibration affects the performance of precision instruments; chatter during machining reduces the surface finish of workpieces, accelerates tool fatigue wear, and in severe cases, affects machine tool life. In engineering, vibration can cause wall cracks in buildings, threatening the overall structural safety of buildings and even causing collapse. In transportation, vibration in vehicles severely impacts passenger experience, and vibration of aircraft wings can potentially cause major flight accidents. Therefore, efficient, highly automated, and stable vibration testing equipment is indispensable. To understand and control vibration, vibration testing must be conducted first.

[0004] In non-contact vibration measurement methods, the Doppler effect using lasers is currently the main approach. The Doppler effect is effective for measuring the vibration velocity of high-frequency vibrating objects. However, when the vibration frequency of the object under test is low, the Doppler frequency shift effect is not very significant, which limits the development of laser vibration measurement technology. Summary of the Invention

[0005] The present invention provides a laser vibration measurement device suitable for 0.1mHz to 10kHz, which can realize a wide range of vibration measurement by using a high-precision charge-coupled device camera and photodetector.

[0006] Therefore, the above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0007] A laser vibration measurement device suitable for 0.1 mHz to 10 kHz, characterized in that: the laser vibration measurement device suitable for 0.1 mHz to 10 kHz includes a laser source, a first polarizing beam splitter, a second polarizing beam splitter, a quarter-wave plate, a beam splitter, a first reflector, a second reflector, a frequency modulation device, a charge-coupled device (CCD) camera, and a photodetector arranged sequentially along the optical path; the laser source is a stable narrow-linewidth single-frequency laser source; the first polarizing beam splitter splits the generated laser into two beams; the second polarizing beam splitter transmits one of the beams to the object under test and receives the measurement beam reflected back from the object under test; the quarter-wave plate is arranged in the first polarizing beam splitter, the second polarizing beam splitter transmits one of the beams to the object under test and receives the measurement beam reflected back from the object under test; the second polarizing beam splitter is arranged in the first polarizing beam splitter, the third polarizing beam splitter, the fourth polarizing beam splitter, the fifth polarizing beam splitter, the sixth polarizing beam splitter, the seventh polarizing beam splitter, the eighth polarizing beam splitter, the first polarizing beam splitter, the second polarizing beam splitter, the first reflector, the second reflector, the fourth reflector, the fifth reflector, the sixth reflector, the seventh reflector, the eighth reflector, the fifth reflector, the sixth reflector, the seventh reflector, the eighth reflector, the eighth reflector, the ninth ... In the transmission optical path of the dual-polarization beam splitter, the polarization direction of the measurement beam is changed. The beam splitter consists of multiple beam splitters to split and combine the reference beam and the measurement beam. The first and second reflectors are used to change the beam propagation direction. The frequency modulation device adjusts the frequency of the second reference beam. The charge-coupled device (CCD) camera is arranged in the output optical path of the third beam splitter. The first reference beam and the first measurement beam interfere on this surface to form alternating bright and dark fringes. When the object vibrates, the alternating bright and dark fringes will move. The CCD camera can detect the change in light intensity at a certain point to measure the number N of the movement of the bright and dark fringes. The vibration displacement of the object under test can be obtained by the following formula:

[0008]

[0009] In the formula: S is the vibration displacement of the object under test, N is the number of fringe movements, and λ is the wavelength of the laser emitted by the laser source; the photodetector is arranged in the output optical path of the fourth beam splitter. When the optical signals of the second reference beam and the second measurement beam undergo frequency aliasing inside the photodetector, a Doppler frequency shift signal can be obtained. The vibration velocity of the object under test can then be obtained using the following formula:

[0010]

[0011] In the formula: Vf is the Doppler frequency shift value, f s Let ν be the frequency of the laser emitted by the laser source, ν be the vibration velocity of the object under test, and c be the speed of light. The vibration frequency f of the vibrating object can be obtained from the vibration velocity and vibration displacement through mathematical calculation. If the vibration values ​​obtained by the charge-coupled device (CCD) camera and the photodetector are both below 1 Hz, the measurement value of the CCD camera is selected as the final measurement result. If the vibration values ​​obtained by the CCD camera and the photodetector are both above 1 Hz, the measurement value of the photodetector is selected as the final measurement result. If the vibration values ​​obtained by the CCD camera and the photodetector are distributed around 1 Hz, the average value of the measurement values ​​of the CCD camera and the photodetector is selected as the final measurement result.

[0012] While adopting the above technical solutions, the present invention may also adopt or combine the following technical solutions:

[0013] As a preferred technical solution of the present invention: the first polarizing beam splitter polarizes the incident laser beam in the horizontal and vertical directions respectively, dividing it into two beams of light with horizontal polarization and vertical polarization.

[0014] As a preferred technical solution of the present invention: the second polarizing beam splitter directly transmits the incident beam in the horizontal polarization direction in its original direction, and changes the propagation direction of the reflected measurement beam in the vertical polarization direction by 90°.

[0015] As a preferred technical solution of the present invention, the beam splitter is composed of 4 beam splitting prisms.

[0016] As a preferred technical solution of the present invention, the frequency modulation device is an acousto-optic modulator based on the principle of Bragg diffraction.

[0017] As a preferred embodiment of the present invention: the charge-coupled device camera measures vibrating objects in the frequency band of 0.1mHz to 1Hz; the photodetector is an avalanche diode, which measures vibrating objects in the frequency band of 1Hz to 10kHz.

[0018] As a preferred technical solution of the present invention: both the charge-coupled device camera and the photodetector can output a current signal that varies with time. For the charge-coupled device camera, given the vibration displacement S of the object, the vibration velocity ν of the object can be obtained through the mathematical relationship ν=s′. For the photodetector, given the vibration velocity ν of the object, the vibration displacement S of the object can be obtained through the mathematical relationship s=∫νdt.

[0019] As a preferred technical solution of the present invention: after the charge-coupled device camera and photodetector obtain the vibration velocity ν and vibration displacement S of the vibrating object, the vibration frequency f of the vibrating object can be obtained by substituting them into the following equation system.

[0020] v=2πfD Equation (3)

[0021] In the formula: ν is the vibration velocity, and D is the amplitude of the vibrating object, that is, the maximum value of the vibration displacement S.

[0022] Compared with existing technologies, the laser vibration measurement device provided by this invention, applicable to 0.1 mHz to 10 kHz, utilizes a high-precision charge-coupled device (CCD) camera to measure alternating bright and dark interference fringes to obtain vibration parameters of low-frequency vibrating objects, and uses a photodetector to measure Doppler frequency shifts to obtain vibration parameters of high-frequency vibrating objects. In the low-frequency range, the laser interferometry method produces clear fringes and demonstrates significant results; in the high-frequency range, the Doppler effect is pronounced and the frequency aliasing method is mature. Furthermore, regardless of whether the obtained vibration parameters are displacement or velocity, they can be mathematically converted into vibration frequencies for vibration measurement. The proposed technology can be widely used for measuring various military targets and precision applications. In civilian measurements, for the minute vibrations of stationary objects such as buildings and engineering facilities at millihertz frequencies, laser ranging requires long-term detection and complex dynamic data analysis to output vibration parameters. The laser interferometry method used in this invention offers advantages such as non-contact measurement, high resolution, and fast measurement speed. For high-speed moving objects such as continuously running machines and engines during startup, laser Doppler measurement offers advantages such as mature technology, high measurement accuracy, and simple data processing. This invention combines laser interferometry and laser Doppler measurement into a single system through optical path design, achieving a balance between measurement range and accuracy. The laser vibration measurement device provided by this invention, applicable to 0.1 mHz to 10 kHz, has the following beneficial effects:

[0023] (1) For vibrating objects with a vibration frequency below 1 Hz, on the one hand, the Doppler effect is not obvious, and the vibration velocity of the object cannot be directly obtained by laser Doppler measurement. On the other hand, the vibrating object at this time often corresponds to a large amplitude and low velocity, and the interference of Doppler frequency shift on the displacement measurement result is small. Therefore, laser interferometry is used to form alternating bright and dark interference fringes, and a high-precision charge-coupled device (CCD) camera is proposed to detect the interference fringes, which can realize high-precision displacement measurement in the low-frequency band. This method makes up for the shortcomings of the Doppler frequency shift vibration measurement method in the low-frequency band, such as insignificant effect, large noise, and low accuracy. For vibrating objects with a vibration frequency above 1 Hz, the signal-to-noise ratio is low when the CCD camera measures the laser interference fringes, and the Doppler frequency shift has a large interference on the displacement measurement of the vibrating object. Therefore, the measured displacement error is large. At this time, the Doppler effect is obvious, and the vibration velocity of the object can be directly obtained by using the frequency aliasing method of photoelectric detector using the Doppler effect, which can realize high-precision velocity measurement in the high-frequency band.

[0024] (2) The device adopts mature optical path and common detection method. The system structure is simple and the components are convenient and intuitive.

[0025] (3) The vibration parameters of the low-frequency band are measured by using laser interferometry combined with charge-coupled device camera, and the vibration parameters of the high-frequency band are measured by using laser Doppler method combined with photodetector. The advantages of each method are fully utilized. Through optical path diagram design, the vibration parameters of the vibrating object can be measured in a wide range of 0.1mHz to 10kHz using only one laser and several common optical devices and detectors, saving costs and space. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the optical path structure of the laser vibration measurement device suitable for 0.1mHz to 10kHz provided by the present invention.

[0027] Among them: 1. Laser source; 2-1 First polarizing beam splitter; 2-2 Second polarizing beam splitter; 3. Quarter-wave plate; 4-1 First beam splitter; 4-2 Second beam splitter; 4-3 Third beam splitter; 4-4 Fourth beam splitter; 5-1 First reflector; 5-2 Second reflector; 6. Frequency modulation device; 7. Charge-coupled device camera; 8. Photodetector. Detailed Implementation

[0028] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0029] Reference Figure 1A laser vibration measurement device suitable for 0.1mHz to 10kHz includes a laser source 1, a first polarizing beam splitter 2-1, a second polarizing beam splitter 2-2, a quarter-wave plate 3, a beam splitter 4, a first reflector 5-1, a second reflector 5-2, a frequency modulation device 6, a charge-coupled device camera 7, and a photodetector 8. Along the optical path, the following components are arranged sequentially: laser source 1, first polarizing beam splitter 2-1, second polarizing beam splitter 2-2, quarter-wave plate 3, beam splitter 4, first reflector 5-1, second reflector 5-2, frequency modulation device 6, charge-coupled device camera 7, and photodetector 8. The second polarizing beam splitter 2-2 is placed on the transmission path of the first polarizing beam splitter 2-1. The quarter-wave plate 3 is placed on the transmission path of the second polarizing beam splitter 2-2. The beam splitter 4 consists of four beam splitters, with the first beam splitter 4-1 placed on the reflection path of the first polarizing beam splitter 2-1, and the second beam splitter 4-2 placed on the reflection path of the second polarizing beam splitter 2-1. In the reflected light path of beam 2, the third polarizing beam splitter 4-3 is placed in the reflected light path of the first beam splitter 4-1 and the transmitted light path of the second beam splitter 4-2; the fourth beam splitter 4-4 is placed in the reflected light path of the first mirror 5-1 and the second mirror 5-2; the first mirror 5-1 is placed in the transmitted light path of the first beam splitter 4-1; the second mirror 5-2 is placed in the reflected light path of the second beam splitter 4-2; the frequency modulation device 6 is placed in the reflected light path of the first beam splitter 5-1; the charge-coupled device camera 7 is placed in the emitted light path of the third beam splitter 4-3; and the photodetector 8 is placed in the emitted light path of the fourth beam splitter 4-4.

[0030] First, the laser emitted from the laser source is split into two polarized beams, one horizontal and one vertical, by the first polarizing beam splitter 2-1. The horizontally polarized beam, as the incident beam of the second polarizing beam splitter 2-2, is transmitted directly in its original direction and passes through the quarter-wave plate 3 to the object under test. The second polarizing beam splitter 2-2 then receives the measurement beam reflected back from the object and reflects the measurement beam. The vertically polarized beam, as the incident beam of the first beam splitter 4-1, is split into a reflected beam (the first reference beam) and a transmitted beam (the second reference beam) by the first beam splitter 4-1. The second beam splitter 4-2 then... The reflected beam to be measured is divided into a transmitted beam, i.e., the first measurement beam, and a reflected beam, i.e., the second measurement beam. The first reference beam and the first measurement beam are combined in the third beam splitter prism 4-3 and then emitted to the charge-coupled device camera 7, where they interfere to form alternating bright and dark fringes. The second reference beam is reflected by the first mirror 5-1 and then passes through the frequency modulation device 6 to become the frequency-modulated second reference beam. The second measurement beam is reflected by the second mirror 5-2 and then combined with the frequency-modulated second reference beam in the fourth beam splitter prism 4-4 before being emitted to the photodetector 8, where frequency aliasing occurs.

[0031] like Figure 1 As shown, laser source 1 is a stable narrow-linewidth single-frequency laser source. The first polarizing beam splitter 2-1 polarizes and splits the incident laser beam in the horizontal and vertical directions respectively. The second polarizing beam splitter 2-2 directly transmits the incident beam in the horizontal polarization direction in its original direction and changes the propagation direction of the reflected vertical polarization measurement beam by 90°. The beam splitter 4 consists of four beam splitters. The frequency modulation device 6 is an acousto-optic modulator based on the Bragg diffraction principle. The charge-coupled device camera 7 is used to measure the vibration of objects in the 0.1mHz to 1Hz frequency band. The photodetector 8 is an avalanche diode, which is used to measure the vibration of objects in the 1Hz to 10kHz frequency band.

[0032] For the light beam emitted to the charge-coupled device camera 7, interference will occur on this surface, forming alternating bright and dark fringes. When the object vibrates, the alternating bright and dark fringes will move. The charge-coupled device camera 7 can detect the change in light intensity passing through a certain point to measure the number of bright and dark fringe movements N. The vibration displacement of the object under test can be obtained by the following formula:

[0033]

[0034] In the formula: S is the vibration displacement of the object under test, N is the number of fringe shifts, and λ is the wavelength of the laser emitted by laser source 1; for the beam emitted to photodetector 8, the beam will undergo frequency aliasing within it to obtain a Doppler frequency shift signal, and the vibration velocity of the object under test can be obtained by the following formula:

[0035]

[0036] In the formula: Vf is the Doppler frequency shift value, f s Let ν be the frequency of the laser emitted by the laser source 1, ν be the vibration velocity of the object under test, and c be the speed of light. After obtaining parameters such as vibration displacement and vibration velocity through the charge-coupled device camera 7 and photodetector 8, the vibration frequency f of the vibrating object can be obtained by substituting them into the following equation system.

[0037] v=2πfD Equation (3)

[0038] In the formula: ν is the vibration velocity, and D is the amplitude of the vibrating object, i.e., the maximum value of the vibration displacement S. If the vibration values ​​obtained by both are below 1Hz, the measurement value of the charge-coupled device camera 7 is selected as the final measurement result; if the vibration values ​​obtained by both are above 1Hz, the measurement value of the photodetector 8 is selected as the final measurement result; if there is an extremely special case where the vibration values ​​obtained by both are distributed around 1Hz, the measurement can be repeated multiple times or the average value of the measurement values ​​of the charge-coupled device camera 7 and the photodetector 8 can be taken as the final measurement result.

[0039] In the field of low-frequency vibration, on the one hand, low frequency often corresponds to large amplitude and low velocity. On the other hand, in addition to measuring vibration velocity, it is also possible to measure the vibration displacement and vibration acceleration of an object. Furthermore, according to the mathematical relationships a=ν′=s″, s=∫νdt, and ν=∫at, these three can be converted into each other. Therefore, the two can be combined, and laser technology can be used to measure the vibration displacement and vibration velocity of the vibrating object respectively. Then, the vibration parameters of the object can be obtained by converting them into vibration frequency through mathematical relationships, thereby realizing large-scale vibration measurement.

[0040] Specifically, this is implemented through the following embodiments:

[0041] Reference Figure 1The laser source, a helium-neon laser, emits a 10mW laser beam with a wavelength of 633nm. This laser beam is first split into two polarized beams by a first polarizing beam splitter 2-1: one with a horizontal power of 8mW and the other with a vertical power of 2mW. The horizontally polarized beam, with a working wavelength of 633nm and a power of 8mW, serves as the incident beam for the second polarizing beam splitter 2-2. It is transmitted directly in its original direction and passes through a quarter-wave plate 3, which has a working wavelength of 633nm and a diameter of 25.4mm, before being projected onto the object under test. The second polarizing beam splitter 2-2 then receives the beam from the object under test. The measuring beam reflected back from the object also reflects the beam to be measured. At this time, due to losses, the power of the beam to be measured is reduced to 2mW. The second beam splitter 4-2 splits the reflected beam to be measured into a transmitted beam, i.e., the first measuring beam (power 1mW), and a reflected beam, i.e., the second measuring beam (power 1mW). The beam splitter operates at a wavelength of 400nm-700nm and has a splitting ratio of 1:1. Vertically polarized light with a power of 2mW is used as the incident light of the first beam splitter 4-1 and is split into a reflected beam, i.e., the first reference beam (power 1mW), and a transmitted beam, i.e., the second reference beam (power 1mW). Then, the first reference beam and the first measurement beam are combined in the third beam splitter prism 4-3 and emitted to the charge-coupled device camera 7 to detect the number of interference fringes. Substituting the number of fringes into equation (1) for calculation, the vibration displacement S of the object under test can be obtained. The vibration velocity ν of the object can be obtained through the mathematical relationship ν = s′. Substituting ν and S into equation (3) for calculation, the vibration frequency f can be obtained. After the second reference beam is frequency-modulated by the frequency-modulating device 6, it is combined with the second measurement beam in the fourth beam splitter prism 4-4 and emitted to the photodetector 8 to detect the frequency shift signal. Substituting the frequency shift value into (2) can obtain the vibration velocity ν of the object under test. The vibration displacement S of the object can be obtained through the mathematical relationship s=∫νdt. After substituting ν and S into equation (3), the vibration frequency f can be obtained. Although two values ​​will be obtained, for the low frequency band below 1Hz, the Doppler effect is not obvious and the result obtained by the laser interferometry method is less affected by the Doppler effect. The high precision of the interference fringes measured by the high-precision charge-coupled device camera is high. Therefore, the result of the laser interferometry method is more accurate as the final result. For the high frequency band above 1Hz, the vibration displacement is difficult to monitor and the Doppler frequency shift effect is more obvious. Therefore, the result of the laser Doppler frequency shift method is more accurate as the final result. Therefore, if the vibration values ​​obtained by both are below 1Hz, the measurement value of the charge-coupled device camera 7 is selected as the final measurement result. If the vibration values ​​obtained by both are above 1Hz, the measurement value of the photodetector 8 is selected as the final measurement result. If there is an extremely special case where the vibration values ​​obtained by both are distributed on both sides of 1Hz, the measurement can be repeated multiple times or the average value of the measurement values ​​of the charge-coupled device camera 7 and the photodetector 8 can be taken as the final measurement result.

[0042] It is evident that this laser vibration measurement device, applicable to 0.1mHz to 1Hz, has a mature optical path, a simple structure, and can increase the range of vibration measurement of the system.

[0043] The present invention provides a laser vibration measurement device applicable to 0.1 mHz to 10 kHz. This device uses a high-precision charge-coupled device (CCD) camera to measure the interference fringes of alternating bright and dark areas to obtain the vibration parameters of low-frequency vibrating objects. It uses a photodetector to measure the Doppler frequency shift to obtain the vibration parameters of high-frequency vibrating objects. Furthermore, regardless of whether the obtained vibration parameters are displacement or velocity, they can be converted into vibration frequency through mathematical relationships to achieve vibration measurement. Therefore, the laser vibration measurement device applicable to 0.1 mHz to 10 kHz of the present invention, using a high-precision CCD camera, can be applied to the vibration measurement of most vibrating objects while ensuring good measurement accuracy, and can significantly improve the range of vibration measurement.

[0044] As will be apparent from the foregoing description, certain aspects of the invention are not limited to the specific details of the examples shown herein, and thus, those skilled in the art will contemplate other modifications and applications or equivalents thereof. The terms “having,” “comprising,” and “including,” and similar terms as used in the foregoing description, are interpreted as “optional” or “may include” rather than “essential.” However, many changes, modifications, variations, and other uses and applications of the invention will be apparent to those skilled in the art upon consideration of the specification and drawings. All such changes, modifications, variations, and other uses and applications that do not depart from the scope and spirit of the invention are considered to be covered by the invention. It should be understood that the examples disclosed herein include any combination and all instances of the features described in any dependent claims.

Claims

1. A laser vibrometer suitable for frequencies from 0.1 mHz to 10 kHz, characterized in that: The system includes a laser source, a first polarizing beam splitter, a second polarizing beam splitter, a quarter-wave plate, a beam splitter, a first reflector, a second reflector, a frequency modulation device, a charge-coupled device (CCD) camera, and a photodetector, arranged sequentially along the optical path. The laser source is a stable, narrow-linewidth, single-frequency laser. The first polarizing beam splitter splits the laser beam into two beams. The second polarizing beam splitter transmits one of these beams to the object under test and receives the measurement beam reflected back from the object. The quarter-wave plate is arranged in the transmission path of the second polarizing beam splitter to change the polarization direction of the measurement beam. The beam splitter, composed of multiple beam splitters, is used to split and combine the reference beam and the measurement beam. The first and second reflectors are used to change the beam propagation direction. The frequency modulation device adds a 40° angle to the second reference beam. The frequency shift is MHz; the charge-coupled device (CCD) camera is arranged on the output optical path of the third beam splitter. The first reference beam and the first measurement beam interfere on this surface to form alternating bright and dark fringes. When the object vibrates, the alternating bright and dark fringes will move. The CCCD camera can detect the change in light intensity passing through a certain point to measure the number of shifts in the bright and dark fringes. The vibration displacement of the object under test can be obtained by the following formula: Equation (1) In the formula: The vibration displacement of the object under test. The number of stripe movements, The wavelength of the laser emitted by the laser source is specified. The photodetector is arranged in the output optical path of the fourth beam splitter. When the optical signals of the second reference beam and the second measurement beam undergo frequency aliasing inside the photodetector, a Doppler frequency shift signal can be obtained. The vibration velocity of the object under test can then be obtained using the following formula: Equation (2) In the formula: This is the Doppler frequency shift value. The frequency at which the laser light source emits laser light. The vibration velocity of the object to be measured. The speed of light is used; the vibration frequency of the vibrating object is obtained by measuring the vibration velocity and vibration displacement. If the vibration values ​​obtained by the charge-coupled device (CCD) camera and the photodetector are both below 1 Hz, the measurement value of the CCD camera is selected as the final measurement result; if the vibration values ​​obtained by the CCD camera and the photodetector are both above 1 Hz, the measurement value of the photodetector is selected as the final measurement result; if the vibration values ​​obtained by the CCD camera and the photodetector are distributed around 1 Hz, the average value of the measurement values ​​of the CCD camera and the photodetector is selected as the final measurement result.

2. The laser vibrometer device suitable for frequencies from 0.1 mHz to 10 kHz according to claim 1, characterized in that: The first polarizing beam splitter polarizes the incident laser beam in the horizontal and vertical directions, respectively, splitting it into two beams: one horizontally polarized and the other vertically polarized.

3. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 1, characterized in that: The second polarizing beam splitter transmits the incident beam in the horizontal polarization direction directly in its original direction, and changes the propagation direction of the reflected measurement beam in the vertical polarization direction by 90°.

4. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 1, characterized in that: The beam splitter consists of four beam splitting prisms.

5. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 1, characterized in that: The frequency modulation device is an acousto-optic modulator (AOM) based on the principle of Bragg diffraction.

6. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 1, characterized in that: The charge-coupled device camera measures vibrating objects in the 0.1 mHz to 1 Hz frequency band; the photodetector is an avalanche diode, which measures vibrating objects in the 1 Hz to 10 kHz frequency band.

7. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 1, characterized in that: Both the charge-coupled device (CCD) camera and the photodetector can output time-varying current signals. For the CCD camera, the displacement of the vibrating object is known. Through mathematical relationships The vibration velocity of the object can be obtained. ; For a photodetector, the vibration velocity of the object is known. Through mathematical relationships The vibration displacement of the object can be obtained. .

8. The laser vibrometer device suitable for 0.1 mHz to 10 kHz according to claim 7, characterized in that: The charge-coupled device (CCD) camera and photodetector obtain the vibration velocity of the vibrating object. and vibration displacement Then, by substituting the following equations and solving the system of equations, the vibration frequency of the vibrating object can be obtained. , Equation (3) In the formula: For vibration velocity, The amplitude of the vibrating object, i.e., the vibration displacement. The maximum value.

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