A device and method for measuring velocity using a composite light dual-beam differential Doppler beam.

Abstract

This invention relates to a device and method for measuring velocity using a composite light dual-beam differential Doppler beam. The measuring device includes: a composite light output unit, a beam splitter, a phase retarder, a first convex lens, a first scattered light receiver, a second scattered light receiver, and a host computer. The composite light output unit outputs composite light, which contains two laser beams with different wavelengths. The beam splitter generates two parallel beams with equal optical path lengths. The first convex lens receives the parallel beams and focuses them onto the surface of the object under test at the measurement point. The phase retarder is positioned along the transmission path of either parallel beam. The first and second scattered light receivers receive the scattered light reflected from the surface of the object under test, generating electrical signals. The host computer acquires the signals output by the first and second scattered light receivers and calculates the magnitude and direction of motion of the object under test at the measurement point. This solution effectively improves the accuracy of velocity measurement.

Description

Technical Field

[0001] This invention relates to the field of velocity measurement technology, and in particular to a device and method for measuring velocity based on composite light dual-beam differential Doppler. Background Technology

[0002] Laser Doppler velocimetry, a key technology in modern measurement, plays a vital role in measuring the velocity of fluids, gases, and solid surfaces due to its non-contact measurement characteristics. With continuous improvements in productivity, this technology is experiencing rapid development in numerous fields, including industrial production, process control, and scientific research, demonstrating its immense application potential across various sectors.

[0003] In practical applications of laser Doppler velocimetry, optical frequency shifting is commonly used to accurately determine velocity direction. Looking back at the development of this technology over the past few decades, optical frequency shifting devices such as rotating gratings, electro-optic crystals, and Bragg cells have been introduced into the velocimetry optical path, undertaking the crucial task of achieving optical frequency shifting. However, while these devices have met the need for direction identification, they have also brought a series of challenging problems. On the one hand, they greatly increase the complexity of the optical path, making what was originally a relatively simple path intricate; on the other hand, the difficulty of adjusting the optical path increases significantly, placing higher demands on the professional knowledge and skills of the operators. More importantly, in practical applications, this complex optical path system is highly susceptible to interference from external factors, such as environmental vibrations, temperature changes, and stray light, which in turn affects the accuracy and stability of the measurement results, limiting the application of laser Doppler velocimetry in situations requiring extremely high precision and stability.

[0004] Regarding laser output, current methods for producing laser output at certain wavelengths rely on frequency doubling of another wavelength using a frequency doubling crystal. For example, the common 532nm laser is generated by frequency doubling a 1064nm laser using a frequency doubling crystal. However, due to the inherent physical limitations of the frequency doubling crystal, its frequency doubling efficiency cannot reach the ideal 100%. This results in the output of the frequency doubling crystal not being a single target wavelength laser, but rather a mixture of the frequency-doubled target wavelength laser and the original wavelength laser. To obtain a pure target wavelength laser that meets usage requirements, a filter is typically used to remove the original wavelength laser.

[0005] Therefore, if this hybrid laser output from the frequency-doubling crystal can be fully and effectively utilized and rationally applied to laser Doppler velocimetry systems, it is expected to provide a completely new solution to overcome the optical path complexity caused by traditional optical frequency shifting devices. This will not only simplify the optical path structure and reduce reliance on the operator's professional skills, but also improve the stability and accuracy of the measurement system, thereby propelling laser Doppler velocimetry technology to a new stage of development.

[0006] Therefore, although laser Doppler velocimetry has achieved remarkable success in many fields, existing methods for velocity direction determination suffer from numerous drawbacks due to the complexity of the optical path. The unique properties of laser output from frequency-doubled crystals offer a potentially effective solution to this problem. Thus, there is an urgent need to propose a new velocimetry scheme to overcome the shortcomings of existing technologies, meet the evolving needs of practical applications, further expand the application scope of laser Doppler velocimetry, and enhance its application efficiency. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a device and method for measuring differential Doppler velocity based on composite light dual beams.

[0008] To achieve the above-mentioned objectives, the present invention provides a composite light dual-beam differential Doppler velocity measurement device, comprising: a composite light output unit, a beam splitter, a phase delay plate, a first convex lens, a first scattered light receiver, a second scattered light receiver, and a host computer;

[0009] The composite light output unit is used to output composite light, wherein the composite light comprises two laser beams with different wavelengths;

[0010] The composite optical output unit includes: a single-mode laser, a frequency-doubled crystal, a second convex lens, a pinhole aperture, and a third convex lens;

[0011] The single-mode laser is used to output a laser beam, and after frequency doubling based on the frequency doubling crystal, it forms a laser beam containing two different wavelengths that are in the same path; and the two different wavelengths of the laser beam that are in the same path are collimated sequentially by the second convex lens, the pinhole aperture and the third convex lens to form the output composite light;

[0012] The beam splitter is used to receive the composite light and generate two parallel beams with equal optical path lengths.

[0013] The first convex lens is used to receive two parallel beams and focus them onto the surface of the object to be measured at the measurement point; wherein, the phase delay plate is disposed on the transmission path of either of the parallel beams;

[0014] The first and second scattered light receivers are used to receive scattered light reflected from the surface of the object under test and generate electrical signals, wherein the first and second scattered light receivers respectively receive scattered light from lasers of different wavelengths;

[0015] The host computer is used to collect the signals output by the first and second scattered light receivers and calculate the speed and direction of motion of the object under test at the measurement point.

[0016] According to one aspect of the invention, the wavelengths of the two laser beams included in the composite light are in an integer ratio.

[0017] According to one aspect of the invention, the phase delay plate is removable and replaceable, used to adjust the interference fringes focused onto the surface of the object under test, so as to control the phase difference between the electrical signals output by the first scattered light receiver and the second scattered light receiver.

[0018] According to one aspect of the present invention, the first scattered light receiver includes: a fourth convex lens, a first filter, and a first photodetector;

[0019] The scattered light reflected from the surface of the object under test passes through the fourth convex lens and the first filter in sequence and is then focused onto the photosensitive surface of the first photodetector.

[0020] The first filter is used to filter the scattered light to keep the scattered light input to the first photodetector a single wavelength.

[0021] According to one aspect of the present invention, the second scattered light receiver includes: a fifth convex lens, a second filter, and a second photodetector;

[0022] The scattered light reflected from the surface of the object under test passes through the fifth convex lens and the second filter in sequence and is then focused onto the photosensitive surface of the second photodetector.

[0023] The second filter is used to filter the scattered light to keep the scattered light input to the second photodetector a single wavelength;

[0024] The second filter filters out light of different wavelengths than the first filter.

[0025] According to one aspect of the invention, two parallel beams generated by the beam splitter are focused by the first convex lens onto the surface of the object to be measured at equal incident angles.

[0026] According to one aspect of the present invention, the velocity of the object to be measured calculated by the host computer is expressed as:

[0027] ;

[0028] in, The wavelength of the laser beam output by the single-mode laser in the composite optical output unit is given. The frequency of the electrical signal output by the first scattered light receiver is [value missing]. The wavelength of the frequency-doubled laser beam is... The frequency of the electrical signal output by the second scattered light receiver. The angle between two laser beams focused onto the surface of the object being tested.

[0029] To achieve the aforementioned objective, this invention provides a measurement method for the aforementioned composite light dual-beam differential Doppler velocity measurement device, comprising the following steps:

[0030] S1. Output composite light, wherein the composite light comprises two laser beams with different wavelengths;

[0031] S2. Receive the composite light and generate two parallel beams with equal optical path lengths;

[0032] S3. Receive two parallel beams and focus them onto the surface of the object to be measured at the measurement point; wherein, a phase delay plate is arranged on the transmission path of either parallel beam to adjust the interference fringes focused onto the surface of the object to be measured.

[0033] S4. Collect the scattered light of two different wavelengths of laser light reflected from the surface of the object under test and generate two different frequency electrical signals;

[0034] S5. Acquire two different frequency electrical signals to calculate the speed of the object under test and determine the direction of motion of the object under test based on the phase difference between the two different frequency electrical signals.

[0035] According to one aspect of the present invention, this method can form two sets of misaligned high-frequency and low-frequency light interference fringes at the measurement point. When the object under test passes sequentially through the high-frequency and low-frequency interference fringes, it can disturb the different interference fringes, thereby enabling the reflected scattered light to carry corresponding velocity information. This allows the scattered light to be converted into a corresponding electrical signal to measure the velocity of the object under test. Furthermore, based on the phase difference between the different interference fringes, the generated electrical signal also maintains the same phase difference, thus enabling the determination of the direction of motion of the object under test. Therefore, this method combines the effects of velocity measurement and motion direction identification. Compared to existing technologies, this method more effectively improves the accuracy of velocity measurement.

[0036] According to one aspect of the present invention, the velocity can be accurately acquired based solely on the physical parameters of the generated laser and the incident angle, effectively avoiding the impact of adding a frequency shifting device on the velocity measurement accuracy, thus giving the present invention superior measurement accuracy.

[0037] According to one aspect of the present invention, this approach also fully realizes the effective utilization of optical energy, resulting in a higher utilization rate of laser energy in this approach. Attached Figure Description

[0038] Figure 1 This is a structural diagram of the composite light dual-beam differential Doppler velocity measurement device of the present invention;

[0039] Figure 2This is a schematic diagram of a set of alternating bright and dark interference fringes formed on the surface of the object to be measured by the composite light dual-beam differential Doppler velocity measurement device of the present invention.

[0040] Figure 3 This is a waveform diagram of the electrical signal obtained by the composite light dual-beam differential Doppler velocity measurement device of the present invention, wherein, Figure 3 (a) shows the electrical signal waveform when the object under test moves in one direction. Figure 3 (b) shows the electrical signal waveform when the object under test moves in the opposite direction.

[0041] In the figure, 1-composite light output unit, 2-beam splitter, 3-phase retarder, 4-first convex lens, 5-first scattered light receiver, 6-second scattered light receiver, 11-single-mode laser, 12-frequency doubling crystal, 13-second convex lens, 14-pinhole aperture, 15-third convex lens, 51-fourth convex lens, 52-first filter, 53-first photodetector, 61-fifth convex lens, 62-second filter, 63-second photodetector. Detailed Implementation

[0042] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the specific embodiments of the present solution will be described in detail below.

[0043] In describing embodiments of the present invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" express orientations or positional relationships based on the orientations or positional relationships shown in the relevant drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on the present invention.

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The embodiments cannot be described in detail here, but the embodiments of the present invention are not limited to the following embodiments.

[0045] like Figure 1As shown, according to one embodiment of the present invention, a composite light dual-beam differential Doppler velocity measurement device includes: a composite light output unit 1, a beam splitter 2, a phase retarder 3, a first convex lens 4, a first scattered light receiver 5, a second scattered light receiver 6, and a host computer. In this embodiment, the composite light output unit 1 is used to output composite light, wherein the composite light includes two laser beams with different wavelengths. Further, the beam splitter 2 is used to receive the composite light and generate two parallel beams with equal optical path lengths. In this embodiment, the first convex lens 4 is used to receive the two parallel beams and focus them onto the surface of the object to be measured at the measurement point. The phase retarder 3 is disposed on the transmission path of either parallel beam. Based on the disposed phase retarder 3, the two wavelength lasers focused on the surface of the object to be measured generate two sets of superimposed interference fringes with a certain misalignment in the bright parts at the measurement point. One set of alternating bright and dark interference fringes generated by one wavelength laser at the measurement point is shown in [reference needed]. Figure 2 As shown, the difference in wavelength between the two laser wavelengths results in a difference between the two sets of alternating bright and dark interference fringes. Furthermore, based on this method, the degree of misalignment between the two sets of interference fringes can be adjusted by replacing the phase delay plate 3, thereby adjusting the phase difference of the generated electrical signal. In this embodiment, the first scattered light receiver 5 and the second scattered light receiver 6 are used to receive scattered light reflected from the surface of the object under test and generate electrical signals. The first scattered light receiver 5 and the second scattered light receiver 6 respectively receive scattered light from lasers of different wavelengths. Based on the different wavelengths of the received lasers, the first scattered light receiver 5 and the second scattered light receiver 6 generate electrical signals with different frequencies, achieving differentiated generation of the two electrical signals. Furthermore, the host computer is used to acquire the signals output by the first scattered light receiver 5 and the second scattered light receiver 6 and calculate the speed and direction of motion of the object under test at the measurement point.

[0046] In this embodiment, the phase retarder 3 can be a planar lens. Based on its different refractive indices for different wavelengths of laser light, it can delay the phase of two wavelengths of laser light in the optical path, thereby generating misaligned interference fringes. Furthermore, in the process of adjusting the degree of misalignment of interference fringes by replacing the phase retarder 3, the function of replacing different phase retarders 3 is to adjust the difference between their refractive indices and those of air, thereby achieving flexible control over the degree of misalignment.

[0047] like Figure 1 As shown, according to one embodiment of the present invention, the wavelengths of the two laser beams included in the composite light are in an integer ratio. In this embodiment, the wavelengths of the two laser beams are in an integer ratio of 2, that is, the wavelength of one of the laser beams (i.e., a portion of the composite light) is consistent with the wavelength of the original incident laser beam, denoted as . λ1. The other laser beam (i.e., the other part of the composite light) is a frequency-doubled laser beam, whose wavelength becomes half the wavelength of the original incident laser beam, denoted as . λ 2, and λ 1=2 λ 2.

[0048] like Figure 1 As shown, according to one embodiment of the present invention, the composite light is formed based on the laser beam being frequency-doubled by a frequency-doubling crystal.

[0049] like Figure 1 As shown, according to one embodiment of the present invention, the composite light output unit 1 includes: a single-mode laser 11, a frequency doubling crystal 12, a second convex lens 13, a pinhole aperture 14, and a third convex lens 15; in this embodiment, the single-mode laser 11 is used to output a laser beam, and after being frequency doubled by the frequency doubling crystal 12, a laser beam containing two different wavelengths and sharing a common path is formed; and the two different wavelengths and sharing a common path laser beam are collimated sequentially by the second convex lens 13, the pinhole aperture 14, and the third convex lens 15 to form the output composite light.

[0050] In this embodiment, the frequency doubling crystal 12 can be in the form of a planar lens to ensure stable output of common-path composite light.

[0051] like Figure 1 As shown, according to one embodiment of the present invention, the phase delay plate 3 is detachable and replaceable, used to adjust the interference fringes focused on the surface of the object under test, thereby controlling the phase difference between the electrical signals output by the first scattered light receiver 5 and the second scattered light receiver 6. In this embodiment, by replacing different phase delay plates 3, different phase delay effects can be achieved for light of different frequencies, which can be used to change the degree of misalignment between interference fringes. Thus, based on the speed of the object under test during its movement, the scattered light reflected by it carries the corresponding speed information. Specifically, after converting the scattered light, the relevant speed information can be converted into the frequency of the electrical signal, realizing the corresponding speed measurement. Furthermore, based on the phase delay effect of the phase delay plate 3, a fixed phase difference can be generated between the converted electrical signals, thereby enabling accurate determination of the direction of motion during the speed measurement process based on the phase difference. This solution achieves the dual effects of speed measurement and direction determination.

[0052] like Figure 1 As shown, according to one embodiment of the present invention, two parallel beams generated by the beam splitter 2 are focused onto the surface of the object to be measured by the first convex lens 4 at equal incident angles, thereby ensuring that the two parallel beams are consistent in incident angles and realizing the accurate and reliable generation of subsequent electrical signals.

[0053] With the above settings, by illuminating the surface of the object under test with equal incident angles, the angle bisectors of the two incident beams can be made perpendicular to the surface of the object under test. This eliminates the need to introduce a scaling factor in the velocity calculation process, making the calculation process simpler. Of course, in different implementations, the angle bisectors of the two incident beams are tilted relative to the surface of the object under test. In this case, a scaling factor needs to be introduced in the velocity calculation process to calculate the velocity of the object from the projection component of the object's velocity in the direction perpendicular to the angle bisector.

[0054] like Figure 1 As shown, according to one embodiment of the present invention, the first scattered light receiver 5 includes: a fourth convex lens 51, a first filter 52, and a first photodetector 53; in this embodiment, the scattered light reflected from the surface of the object to be measured passes through the fourth convex lens 51 and the first filter 52 in sequence and is focused onto the photosensitive surface of the first photodetector 53; wherein, the first filter 52 is used to filter the scattered light so as to keep the scattered light input to the first photodetector 53 as a single wavelength.

[0055] In this embodiment, the first photodetector 53 is located on the focal plane of the fourth convex lens 51 to achieve clear imaging of the beam converged by the fourth convex lens 51.

[0056] like Figure 1 As shown, according to one embodiment of the present invention, the second scattered light receiver 6 includes: a fifth convex lens 61, a second filter 62, and a second photodetector 63. In this embodiment, the scattered light reflected from the surface of the object under test passes sequentially through the fifth convex lens 61 and the second filter 62 before being focused onto the photosensitive surface of the second photodetector 63. The second filter 62 is used to filter the scattered light to maintain the scattered light input to the second photodetector 63 as a single wavelength. In this embodiment, the wavelengths of the light filtered by the second filter 62 and the first filter 52 are different. For example, the wavelength of the light filtered by the first filter 52 is... λ 2. The wavelength of the light filtered out by the second filter 62 is . λ 1.

[0057] In this embodiment, the second photodetector 63 is located on the focal plane of the fifth convex lens 61 to achieve clear imaging of the beam converged by the fifth convex lens 61.

[0058] According to one embodiment of the present invention, the velocity of the object to be measured calculated by the host computer is expressed as:

[0059] ;

[0060] in, The wavelength of the laser beam output by the single-mode laser 11 in the composite optical output unit 1 is given. The frequency of the electrical signal output by the first scattered light receiver 5 is... The wavelength of the frequency-doubled laser beam is... The frequency of the electrical signal output by the second scattered light receiver 6 is... The angle between two laser beams focused onto the surface of the object being tested.

[0061] With the above settings, this solution can achieve accurate velocity acquisition based solely on the physical parameters of the generated laser and the incident angle, effectively avoiding the influence of external environmental variables on the velocity measurement accuracy, thus giving this solution superior measurement accuracy.

[0062] According to one embodiment of the present invention, a measurement method using the aforementioned composite light dual-beam differential Doppler velocity measurement device includes the following steps:

[0063] S1. Output composite light, wherein the composite light contains two laser beams with different wavelengths;

[0064] S2. Receives the composite light and generates two parallel beams with equal optical path lengths;

[0065] S3. Receive two parallel beams and focus them onto the surface of the object to be measured at the measurement point; wherein, a phase delay plate 3 is arranged on the transmission path of either parallel beam to adjust the interference fringes focused onto the surface of the object to be measured.

[0066] S4. Collect the scattered light of two different wavelengths of laser light reflected from the surface of the object under test and generate two different frequency electrical signals;

[0067] S5. Acquire two different frequency electrical signals to calculate the speed of the object under test and determine the direction of motion of the object under test based on the phase difference between the two different frequency electrical signals.

[0068] like Figure 1 As shown, according to one embodiment of the present invention, in step S1, the composite light is generated based on the composite light output unit 1, wherein the wavelengths of the two laser beams included in the composite light are in an integer ratio. In this embodiment, the wavelengths of the two laser beams are in an integer ratio of 2.

[0069] like Figure 1 As shown, according to one embodiment of the present invention, in step S2, two parallel beams with equal optical path are generated based on beam splitter 2.

[0070] like Figure 1As shown, according to one embodiment of the present invention, in step S3, the first convex lens 4 receives two parallel beams and focuses them onto the surface of the object to be measured at the measurement point. The phase delay plate 3 is disposed on the transmission path of either parallel beam. Based on the disposed phase delay plate 3, the two wavelength lasers focused on the surface of the object to be measured generate two sets of superimposed interference fringes at the measurement point, with a certain degree of misalignment in the bright part. Furthermore, based on this method, the degree of misalignment of the interference fringes can be adjusted by replacing the phase delay plate 3, thereby achieving subsequent adjustment of the phase difference of the generated electrical signal.

[0071] In this embodiment, each set of interference fringes is formed by the interference of two laser beams with a single wavelength and a phase difference. The two wavelengths of laser light formed by the frequency doubling crystal 12 can form two sets of interference fringes based on the same principle. In this embodiment, the two sets of interference fringes are superimposed on the surface of the object under test at the measurement point, but due to the phase difference, the bright areas between the two sets of interference fringes also exhibit a certain degree of misalignment.

[0072] In this embodiment, the density of each set of interference fringes is determined by the incident angle and wavelength of the two laser beams of the same wavelength that form the interference. The two wavelengths are multiplied by a factor of 2, ensuring that the fringe densities of the two sets of interference fringes are equal to or close to a factor of 2. Furthermore, the introduction of the phase retardation plate 3 allows the two sets of interference fringes to exhibit a certain degree of misalignment when superimposed at the measurement point, enabling the determination of direction during velocity measurement.

[0073] like Figure 1 As shown, according to one embodiment of the present invention, in step S4, the first scattered light receiver 5 and the second scattered light receiver 6 are used to receive the scattered light reflected by the surface of the object to be tested and generate an electrical signal. The first scattered light receiver 5 and the second scattered light receiver 6 respectively receive scattered light from lasers of different wavelengths. The first scattered light receiver 5 and the second scattered light receiver 6 generate electrical signals with different frequencies based on the different wavelengths of the lasers they receive, thereby realizing the differentiated generation of two electrical signals.

[0074] like Figure 1 As shown, according to one embodiment of the present invention, in step S5, the velocity of the object to be measured at the measurement point is calculated based on the signals output by the first scattered light receiver 5 and the second scattered light receiver 6 collected by the host computer; wherein, the velocity of the object to be measured calculated by the host computer is expressed as:

[0075] ;

[0076] in, The wavelength of the laser beam output by the single-mode laser 11 in the composite optical output unit 1 is given. The frequency of the electrical signal output by the first scattered light receiver 5 is... The wavelength of the frequency-doubled laser beam is... The frequency of the electrical signal output by the second scattered light receiver 6 is... The angle between two laser beams focused onto the surface of the object being tested.

[0077] like Figure 3 As shown, when the object under test moves in one direction, there is a phase difference between the high-frequency electrical signal generated by the short-wavelength optical signal and the low-frequency electrical signal generated by the long-wavelength optical signal. The output electrical signal is as follows: Figure 3 As shown in (a), when the object under test moves in another direction, the output electrical signal is as follows: Figure 3 As shown in (b), in comparison Figure 3 (a) and Figure 3 As shown in (b), due to the existence of phase difference, the amplitude of the high-frequency electrical signal and the low-frequency electrical signal of the object under test in different directions exhibits the "leading" characteristic in different directions. Therefore, the direction of motion of the object under test can be determined based on the order of appearance of the amplitudes of the two electrical signals.

[0078] The above description is merely an example of a specific solution of the present invention. For any devices and structures not described in detail herein, it should be understood that they are implemented using common devices and methods already available in the art.

[0079] The above description is merely one embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite light dual-beam differential Doppler velocity measurement device, characterized in that, include: Composite optical output unit (1), beam splitter (2), phase delay plate (3), first convex lens (4), first scattered light receiver (5), second scattered light receiver (6) and host computer; The composite light output unit (1) is used to output composite light, wherein the composite light contains two laser beams with different wavelengths; The composite optical output unit (1) includes: a single-mode laser (11), a frequency doubling crystal (12), a second convex lens (13), a pinhole aperture (14), and a third convex lens (15). The single-mode laser (11) is used to output a laser beam, and after frequency doubling based on the frequency doubling crystal (12), a laser beam containing two different wavelengths and in the same path is formed; and the two different wavelengths and in the same path are collimated by the second convex lens (13), the pinhole aperture (14) and the third convex lens (15) in sequence to form the output composite light; The beam splitter (2) is used to receive the composite light and generate two parallel beams with equal optical path lengths; The first convex lens (4) is used to receive two parallel beams and focus them onto the surface of the object to be measured at the measurement point; wherein, the phase delay plate (3) is disposed on the transmission path of either of the parallel beams; The first scattered light receiver (5) and the second scattered light receiver (6) are used to receive the scattered light reflected by the surface of the object to be tested and generate an electrical signal. The first scattered light receiver (5) and the second scattered light receiver (6) respectively receive scattered light from lasers of different wavelengths. The host computer is used to collect the signals output by the first scattered light receiver (5) and the second scattered light receiver (6) and calculate the speed of the object to be measured and the direction of motion of the object to be measured at the measurement point.

2. The composite light dual-beam differential Doppler velocity measurement device according to claim 1, characterized in that, The wavelengths of the two laser beams contained in the composite light are in an integer ratio.

3. The composite light dual-beam differential Doppler velocity measurement device according to claim 1, characterized in that, The phase delay plate (3) is detachable and replaceable, used to adjust the interference fringes focused on the surface of the object under test, so as to control the phase difference between the electrical signals output by the first scattered light receiver (5) and the second scattered light receiver (6).

4. The composite light dual-beam differential Doppler velocity measurement device according to claim 3, characterized in that, The first scattered light receiver (5) includes: a fourth convex lens (51), a first filter (52) and a first photodetector (53); The scattered light reflected from the surface of the object under test passes through the fourth convex lens (51) and the first filter (52) in sequence and is then focused onto the photosensitive surface of the first photodetector (53); The first filter (52) is used to filter the scattered light so as to keep the scattered light input to the first photodetector (53) a single wavelength.

5. The composite light dual-beam differential Doppler velocity measurement device according to claim 4, characterized in that, The second scattered light receiver (6) includes: a fifth convex lens (61), a second filter (62), and a second photodetector (63); The scattered light reflected from the surface of the object under test passes through the fifth convex lens (61) and the second filter (62) in sequence and is then focused onto the photosensitive surface of the second photodetector (63); The second filter (62) is used to filter the scattered light to keep the scattered light input to the second photodetector (63) a single wavelength; The second filter (62) filters out light with different wavelengths than the first filter (52).

6. The composite light dual-beam differential Doppler velocity measurement device according to claim 1, characterized in that, The two parallel beams generated by the beam splitter (2) are focused onto the surface of the object to be measured by the first convex lens (4) at equal incident angles.

7. The composite light dual-beam differential Doppler velocity measurement device according to claim 1, characterized in that, The velocity of the object to be measured, calculated by the host computer, is expressed as: in, The wavelength of the laser beam output by the single-mode laser (11) in the composite optical output unit (1) is given by the wavelength of the laser beam. The frequency of the electrical signal output by the first scattered light receiver (5) is... The wavelength of the frequency-doubled laser beam is... The frequency of the electrical signal output by the second scattered light receiver (6) is... The angle between two laser beams focused onto the surface of the object being tested.

8. A measurement method using the composite light dual-beam differential Doppler velocity measuring device according to any one of claims 1 to 7, characterized in that, Including the following steps: S1. Output composite light, wherein the composite light comprises two laser beams with different wavelengths; S2. Receive the composite light and generate two parallel beams with equal optical path lengths; S3. Receive two parallel beams and focus them onto the surface of the object to be measured at the measurement point; wherein, a phase delay plate (3) is arranged on the transmission path of either parallel beam to adjust the interference fringes focused onto the surface of the object to be measured. S4. Collect the scattered light of two different wavelengths of laser light reflected from the surface of the object under test and generate two different frequency electrical signals; S5. Acquire two different frequency electrical signals to calculate the speed of the object under test and determine the direction of motion of the object under test based on the phase difference between the two different frequency electrical signals.

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