Method for detecting ultrasonic cavitation by means of laser interferometry and device therefor

Abstract

The application relates to a method and device for detecting ultrasonic cavitation by laser interference, which receives interference light of first laser and second laser by an interference light receiver; the first laser generator, the second laser generator and the interference light receiver are fixedly installed on a platform; the interference light receiver is a photosensitive diode array and an oscilloscope or a CMOS array and an oscilloscope; only the first laser generator is turned on to make the first laser pass through a focusing area of an ultrasonic focusing transducer array; if the laser light intensity received by the photosensitive diode array light receiver changes compared with the interference light when the ultrasonic focusing transducer array is not started, it is determined that the first laser passes through a larger ultrasonic cavitation bubble; if the interference light received by the photosensitive diode array receiver does not change compared with the interference light when the ultrasonic focusing transducer array is not started, it is determined that the first laser does not have ultrasonic cavitation bubbles or generates smaller cavitation bubbles.

Description

Technical Field

[0001] This application relates to ultrasonic cavitation detection technology, and more particularly to a method and apparatus for detecting ultrasonic cavitation using laser interferometry. Background Technology

[0002] Focused ultrasound systems typically generate heating points and cavitation effects at the focal point based on their intensity. In water, this results in the continuous generation, explosion, and disintegration of bubbles. By adjusting the energy supply intensity, the size of the bubble cluster can be increased from a sphere with a diameter of 0.01 mm to a sphere with a diameter of 10 mm.

[0003] Current detection methods mostly involve directly detecting the vibrations generated by the explosion of cavitation bubbles, often using acoustic devices. However, for devices with a focal point close to the transducer, acoustic detection is affected by the transducer's own vibrations, leading to a significant decrease in detection accuracy.

[0004] Laser sensors are used in factories to detect leaks in equipment. This detection is based on laser attenuation. After the laser passes through the gas being tested via a reflection circuit, some of the light is absorbed by the leaking gas, causing the final detected laser light to attenuate, thus determining a gas leak. However, in ultrasonic cavitation, the laser attenuation is insufficient for detection at cavitation points that are only a few millimeters in size and experience a momentary vacuum. Summary of the Invention

[0005] In view of the above problems, this application proposes a method and apparatus for detecting ultrasonic cavitation using laser interferometry.

[0006] This application proposes a method for detecting ultrasonic cavitation using laser interferometry, comprising:

[0007] A first laser is generated using a first laser generator, and a second laser is generated using a second laser generator; the first and second lasers have the same frequency; a photodiode array receives the first laser and its scattered light; a CMOS interference light receiver receives the interference light between the first and second lasers; the first optical path traversed by the first laser and the second optical path traversed by the second laser are the same; the first laser generator, the second laser generator, and the CMOS interference light receiver are fixedly mounted on a platform, and the receiver can be interchanged with the photodiode array receiver; the CMOS interference light receiver and the photodiode array are respectively connected to their oscilloscopes.

[0008] The first laser is activated and passed through the focusing area of ​​the ultrasonic generator array. If the intensity of the laser light received by the photodiode array optical receiver changes compared to the interference light when the ultrasonic generator array is not activated, it is determined that the first laser has passed through a large ultrasonic cavitation bubble. If the interference light received by the photodiode array optical receiver does not change compared to the interference light when the ultrasonic generator array is not activated, it is determined that the first laser has no ultrasonic cavitation bubble or has generated a small cavitation bubble. Then, the photodiode array optical receiver is replaced with a CMOS array optical receiver, and the second laser is activated. If the interference light received by the CMOS array optical receiver changes compared to the interference light when the ultrasonic generator array is not activated, it is determined that the first laser has passed through a small ultrasonic cavitation bubble.

[0009] Preferably, the position and range of the ultrasonic cavitation bubbles are determined by translating or rotating the platform.

[0010] Preferably, the waveform of the CMOS array oscilloscope is W = W0cosθ + e + e0, where W0 is the rate of light path deformation caused by light refraction after bubble formation, θ is the initial position, e is the systematic error (since the semiconductor laser has an unstable state of 1-2 ns between startup and stabilization, this error cannot be avoided when the cavitation bubble appears less than 30 cm from the light source, and this distance should be left as much as possible when setting the light source), and e0 is the random error; waveforms W1, W2, W4, and W5 are obtained by translating or rotating the platform.

[0011] θ = arctan(W4 - W2) / (W1 - W5), where,

[0012] W1 = W0 cosθ + e + e0,

[0013] W2= W0 cos(θ+90°)+e+e0=-W0sin θ+e+e0,

[0014] W4= W0cos(θ+270°)+e+e0= W0sin θ+e+e0,

[0015] W5= W0 cos(θ+180°)+e+e0=-W0cos θ+e+e0;

[0016] W0 = (W4 - W2) / 2sinθ;

[0017] The θ of the interference light and the deformation rate W0 of the light path can be deduced from the oscilloscope waveforms at various angles. Since R is the bubble radius and λ is the speed of light in the bubble size parameter a = 2πR / λ, and the radius of the tiny bubble is on the order of 10μm-1mm, its scattered light is very weak. The change in optical path is mainly affected by the change in the refracted light path caused by the laser passing through the bubble. Based on the refractive index of the medium and the optical path deformation rate W0, and by measuring the time interval of the changing waveform and the phase change of the changing waveform when the ultrasonic focusing array is working, the size of the laser path within the bubble can be obtained. By comparing the time difference between the waveform change and the trigger signal, the distance between the bubble and the laser source can be determined.

[0018] Preferably, by comparing the difference in waveform W on the photodiode array oscilloscope when the first optical path passes through the ultrasonic cavitation bubble and when it does not, the laser will scatter after passing through a larger ultrasonic cavitation bubble. The waveform of the photodiode array switches to a position deviating from the laser optical path, and the scattered light signal is obtained:

[0019] I(θ',Ψ)=I0λ 2 (i1sin 2 Ψ+i2cos 2 Ψ) / (4π 2 r 2 )

[0020] Where Ψ is the angle between the incident photoelectric vector and the observation plane, and i1 and i2 are intensity distribution functions, which are fitted by fixing the angle θ' between the scattered light and the incident light and generating cavitation bubbles of the same size in the water medium with focused ultrasound of the same intensity. When in different media, the bubble size parameters remain unchanged, and their relationship with the refractive index also needs to be refitted.

[0021] When the cavitation bubble is small, the waveform obtained by interferometry between the first and second optical paths is compared with the waveform when no cavitation occurs. The waveform difference when the negative pressure peak of the cavitation region is 10 MPa is defined as the reference unit. The intensity of the ultrasonic cavitation bubble on the optical path can be determined by measuring the waveform difference under other conditions.

[0022] Preferably, a synchronous time trigger signal generator simultaneously transmits trigger signals to the ultrasonic excitation pulse generator and the laser pulse generator, records the waveforms of the optical receivers of the focused ultrasonic transducer array when it is activated and when it is not activated, finds the time when the waveform changes as the first time, and the difference between the first time and the adjacent trigger signal is the time when the ultrasonic cavitation bubble appears.

[0023] This application also proposes a device for detecting ultrasonic cavitation using laser interferometry, comprising:

[0024] The system comprises a first laser generator, a second laser generator, a CMOS array interference optical receiver and its oscilloscope, a photodiode array optical receiver and its oscilloscope, an ultrasonic generator array, a water tank, an optical path control box, and a reflector.

[0025] The first laser generator, the second laser generator, and the interference light receiver are mounted on the platform; this platform is a three-degree-of-freedom mobile platform.

[0026] A first laser generator generates a first laser beam, and a second laser generator generates a second laser beam. The first and second laser beams have the same frequency. A photodiode array optical receiver receives the laser beam from the first laser generator and its scattered light. A CMOS interference optical receiver receives the interference light between the first and second laser beams. The first optical path traversed by the first laser beam and the second optical path traversed by the second laser beam have the same path length. The first laser generator, the second laser generator, and the interference optical receiver are fixedly mounted on the platform. Each optical receiver is connected to its oscilloscope.

[0027] An ultrasonic generator array is installed in a water tank; a platform equipped with a first laser generator, a second laser generator, and an interference light receiver is located in the water tank, which contains experimental liquid; the platform can move and rotate relative to the water tank.

[0028] The first laser passes through the focusing area of ​​the ultrasonic generator array; if the interference light received by the interference light receiver changes compared to the interference light when the ultrasonic generator array is not activated, it is determined that the first laser has passed through the ultrasonic cavitation bubble; if the interference light received by the interference light receiver does not change compared to the interference light when the ultrasonic generator array is not activated, it is determined that the first laser has not passed through the ultrasonic cavitation bubble.

[0029] Preferably, the first optical path and the second optical path each include an optical fiber path length control box and a reflector, which are used to adjust the corresponding optical paths so that the first optical path and the second optical path have the same path length.

[0030] This application determines the presence of ultrasonic cavitation bubbles by using laser interference to detect the influence of ultrasonic cavitation bubbles, overcoming the influence of vibration on the ultrasonic generator array in traditional acoustic detection methods. In addition, the method and device of this application can also determine the location, range, occurrence time and intensity of ultrasonic cavitation bubbles. For the problem that small-diameter cavitation bubbles from 0.01 mm to 10 mm are difficult to detect by light intensity changes, a three-degree-of-freedom interferometric optical loop detection method is adopted, which provides corresponding data basis for the development of small short-focal-length ultrasonic focusing equipment. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the boundary of an ultrasonic cavitation bubble.

[0032] Figure 2 The location and extent of ultrasonic cavitation bubbles;

[0033] Figure 3 This is a flowchart of an embodiment of the method for detecting ultrasonic cavitation using laser interferometry according to this application;

[0034] Figure 4 This is a schematic diagram of the apparatus for detecting ultrasonic cavitation using laser interferometry in experimental optical path A, according to this application.

[0035] Figure 5 This is a schematic diagram of the apparatus for detecting ultrasonic cavitation using laser interferometry in experimental optical path B, according to this application.

[0036] Figure 6 This is a schematic diagram of the device for detecting ultrasonic cavitation using laser interferometry according to this application.

[0037] Figure 7 This is a schematic diagram of the device for detecting ultrasonic cavitation using laser interferometry according to this application. Detailed Implementation

[0038] The present application will now be described in detail with reference to the accompanying drawings.

[0039] This invention relates to a three-degree-of-freedom interferometer based on a three-coordinate moving platform and a ring-shaped short-focal-length ultrasonic focusing array. The three-degree-of-freedom interferometer consists of two 0.6mm semiconductor laser emitters, a positioning plate, a reflector, a CMOS interference optical path receiver, fiber optic coils, an oscilloscope, and a three-degree-of-freedom robotic arm. The structure ensures that the optical paths from the two laser emitters to the receiver have equal distances. When the measurement structure is too small, the amplification effect of the refracted optical path is increased. The ring-shaped short-focal-length ultrasonic focusing array consists of a power supply, an ultrasonic generator, a ring-shaped focal length fixing fixture, and 8-12 ultrasonic transducers. It can generate cavitation effects at equal time intervals based on the input signal for detection.

[0040] The measurement measures tiny cavitation bubbles generated by a controllable focal ultrasonic focusing transducer array. These bubbles range in size from 0.01 mm to 10 mm. The size of the cavitation bubbles can be changed by controlling the energy input to the transducer. The transducer can generate a self-feedback waveform. It is generally believed that the generation of cavitation bubbles is related to the working waveform in the self-feedback waveform. Within a certain frequency range, the higher the amplitude of the self-feedback waveform, the greater the energy, and the faster and larger the tiny bubbles are generated, resulting in a faster change in the refracted light path. This causes the waveform amplitude displayed by the interference receiver to increase. When the transducer is in the working waveform, its energy is transferred to the focal point to generate cavitation. The time involved is negligible due to the short focal length. Therefore, it is believed that the interference waveform and the self-feedback waveform are highly correlated, and the self-feedback waveform is used as the basis for adjusting the oscilloscope of the interference receiver.

[0041] The three-degree-of-freedom motion platform consists of three high-precision stepper motors and lead screws. It enables the interferometer to move and provides the spatial coordinates of the interferometer during measurement, thus quantifying the spatial position, range, and relative position of the cavitation bubble cluster with respect to the ultrasonic focusing transducer.

[0042] Two semiconductor lasers are used with an ultra-fine laser exciter. One detection laser emits light that passes through the detection point, while the other interference laser emits light that does not pass through the detection point. However, the two beams reach the same endpoint and form interference. The laser parameters of the two lasers can be kept consistent to facilitate measurement and calculation.

[0043] The interference light receiver uses a photosensitive material array to convert the received interference light into an electrical signal and output it to an oscilloscope. Alternatively, a CMOS sensor array can be used to detect the interference result.

[0044] The interferometer is equipped with an orifice plate and a detachable high-precision circular slide rail, which are mainly used to ensure that the two optical paths are of the same length during experimental measurement, thus ensuring the effectiveness of the interference.

[0045] The adjustable fiber optic path module consists of a fiber coil and a blocking shield. It is mainly used to adjust the optical path distance between the two laser beams during measurement. The size of the cavitation bubble will change, which will cause the interference optical path distance required for the interference light to change. At this time, the length of the access fiber is adjusted to control the total optical path length within the required range.

[0046] The numerical conversion software provides control of the three-coordinate moving platform, as well as the storage and mapping of its coordinates, and automatically calculates the relative cavitation intensity of each cavitation bubble cluster according to the above calculation method, for testing and adjustment of the ultrasonic focusing transducer array.

[0047] A ring-shaped short-focal-length ultrasonic focusing array is fixed in a water tank, with its working focus fixed within the detection range. The cavitation point is generally considered to be an ellipsoid. A three-degree-of-freedom interferometer is adjusted, and interference waveforms are detected using loop A along the focal line of the ring-shaped short-focal-length ultrasonic focusing array. If a cavitation point appears, it must be on this focal line. Interference waveforms are obtained when the ring-shaped short-focal-length ultrasonic focusing array is working and when it is not working. The interference waveform is W = W0cosθ + e + e0, where W0 is the rate of light path deformation caused by light refraction after bubble formation, θ is the initial position, e is the systematic error, and e0 is the random error. The output efficiency of the interference receiver decreases as the optical path length increases. The optical path length attenuation must be controlled within 20%; otherwise, excessive error will render the data unusable when adjusting the transducer. During detection, the two optical paths must be adjusted to the same length, X1 = X2. Errors in path length will significantly affect the accuracy of the obtained data.

[0048] If small cavitation bubbles are generated, the laser light will be refracted after passing through, causing a change in the optical path and resulting in interference with another optical path. By observing the changes in the interference waveform when the annular short focal length ultrasonic focusing array is working and not working, the time of cavitation generation and the threshold of the cavitation waveform can be obtained.

[0049] Based on this threshold, by using a three-coordinate moving platform to move the interferometer, the coordinates of the cavitation effect on the ZY plane, as well as the maximum circular area and shape of the ellipse of the focal line of the annular short focal length ultrasonic focusing array, can be obtained on the basis of loop A.

[0050] After measuring the ZY plane, use a three-coordinate moving platform to adjust the interferometer to loop B, so that the optical path is perpendicular to the focal line of the annular short focal length ultrasonic focusing array for detection. To measure the position of the cavitation point on the XY plane, the focal distance needs to be estimated from the transducer parameters first. Then, from the estimated position, use the three-coordinate moving platform to move along the focal line of the annular short focal length ultrasonic focusing array to find the point with the largest waveform change, which is the cavitation center. Measure other waveform change points in sequence, and then the position and range of the cavitation point in the XY plane can be plotted using software.

[0051] Since cavitation efficiency is reflected in the generation efficiency and size of cavitation bubbles, it directly affects the refraction of laser light in the bubbles. The shorter the existence time of each bubble, the more complex the laser refraction circuit, and the greater the deviation of the laser interference waveform from when it is not working. Therefore, this device can also detect the intensity of cavitation, providing data support for adjusting various electronic parameters and operating parameters of the small annular short focal length ultrasonic focusing array.

[0052] If it is necessary to eliminate experimental errors, the experimental circuit AB can be rotated around its measurement direction, and the value of W can be corrected by inverse kinematics.

[0053] The specific steps of the method in this application are as follows:

[0054] Step 1: Set up the ultrasonic focusing array and use a self-feedback oscilloscope to confirm the operation of the ultrasonic transducer.

[0055] Step 2: Set up experimental circuit A using an interferometric ultrasonic detector and measure the waveforms of the interferometric receiving instrument when the transducer is working and when it is not working.

[0056] Step 3: Move the three-degree-of-freedom platform and use experimental optical path A to move it on the ZOY plane. Compare the waveform with the waveform when the transducer was not working. If the waveforms are different, it means that the detection point is still within the cavitation point. Based on the moving coordinates, draw the maximum interface of the cavitation bubble cluster on the ZOY plane. This involves two experimental optical path designs, specifically:

[0057] Experimental optical path A: consists of two semiconductor lasers, two fiber optic path control boxes, a reflector, an ultrasonic focusing transducer array, an interferometric receiver, and its oscilloscope. One of the lasers is placed along the focal line of the ultrasonic focusing transducer array, because cavitation must occur along this focal line. Since the optical path length affects the conversion rate of the interferometric receiver, the equipment is first adjusted to a suitable optical path length using a three-degree-of-freedom platform, and then its position on the ZOY plane is adjusted to measure the boundary of the cavitation range.

[0058] Experimental optical path B: It is modified from experimental optical path A. The probe beam is perpendicular to the focal line of the ultrasonic focusing transducer array. After adjusting the length of the optical path, it moves in the XOY plane to detect the position and range of cavitation bubble clusters in the XOY plane.

[0059] Step 4: Adjust the interferometer and move experimental loop B on the ZOX plane. Compare the waveform with the waveform when the transducer was not working. If the waveforms are different, it means the probe point is still within the cavitation point. Based on the moving coordinates, draw the maximum interface of the cavitation bubble cluster on the ZOY plane. Combine the two interfaces to generate the position and range of the cavitation bubble cluster, specifically:

[0060] 1) Compare the working states to obtain the bubble cluster boundaries on the two planes, and generate their boundary maps, such as... Figure 1 As shown;

[0061] 2) Based on the coordinates of the three-degree-of-freedom moving platform, plot the position and range of the bubble cluster relative to the ultrasound focusing alignment, such as... Figure 2 As shown;

[0062] Step 5: Process the oscilloscope data, extract a segment of the waveform whose appearance time is similar to the ultrasonic excitation pulse emission time. By comparing the time difference between the two, the time difference from pulse emission to response can be obtained. The waveform when not in operation can be used as a reference to calculate the cavitation intensity. The specific calculation is as follows:

[0063] 1) The oscilloscope waveform W = W0cosθ + e + e0, where W0 is the rate of light path deformation caused by light refraction after bubble formation, θ is the initial position, e is the systematic error, and e0 is the random error.

[0064] 2) The output of the interference light receiver is P = P0(1 + cosΔØR), where ΔØR is the phase difference introduced by the fiber optic path control box.

[0065] 3) The output of the interference light receiver is affected by the length of the optical path. Among them, the fiber wound in the fiber optic control box has the most significant impact on the length of the optical path. ΔØR = 2LΠD / (λc), where λ is the wavelength in vacuum, L is the length of the optical path, and D is the diameter of the fiber coil.

[0066] 4) Modulate the receiver output with a square wave: ΔP(ΔØR, Øb) = 2P0sin ØbsinΔØR. The sensitivity reaches its maximum when Øb = Π / 2, at which point I′ = I0[1 + cos(ΔØR + Øb)].

[0067] 5) Calculation of the initial angle θ: The highest point of the cavitation bubble cluster amplitude is generally located at the center of the sphere at the beginning of the cavitation jet range. This part of the cavitation bubble can be approximated as a sphere. A three-coordinate moving platform is used to perform multiple measurements around this sphere, typically at 0°, 90°, 180°, and 270°.

[0068] W1 = W0 cosθ + e + e0,

[0069] W2= W0 cos(θ+90°)+e+e0=-W0sin θ+e+e0,

[0070] W4= W0cos(θ+270°)+e+e0= W0sin θ+e+e0,

[0071] W5= W0 cos(θ+180°)+e+e0=-W0cos θ+e+e0;

[0072] Therefore, tan θ = (W4 - W2) / (W1 - W5).

[0073] Therefore, θ = arctan(W4 - W2) / (W1 - W5)

[0074] Then use θ to solve for W0 = (W4 - W2) / 2sinθ

[0075] Unless otherwise defined, all technical and / or scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this invention relates. The materials, methods, and embodiments mentioned in this application are illustrative only and not restrictive.

[0076] Although the present invention has been described in conjunction with specific embodiments, those skilled in the art can make appropriate substitutions, modifications and changes within the inventive spirit of this application, and such substitutions, modifications and changes still fall within the protection scope of this application.

Claims

1. A method for detecting ultrasonic cavitation using laser interferometry, comprising: A first laser is generated using a first laser generator, and a second laser is generated using a second laser generator; the first and second lasers have the same frequency; an interference light receiver receives the interference light from the first and second lasers; the first optical path traversed by the first laser and the second optical path traversed by the second laser have the same path length; the first laser generator, the second laser generator, and the interference light receiver are fixedly mounted on a platform; the interference light receiver is a CMOS array and an oscilloscope; the intensity of the first laser and its scattered light is received using a photodiode array and an oscilloscope. Only the first laser is turned on, and the first laser is passed through the focusing area of ​​the ultrasonic focusing transducer array. If the laser intensity received by the photodiode array changes compared to the laser intensity when the ultrasonic focusing transducer array is not turned on, it is determined that the first laser has passed through a large ultrasonic cavitation bubble. If the laser intensity received by the photodiode array does not change compared to the laser intensity when the ultrasonic focusing transducer array is not turned on, it is determined that the first laser has not passed through the ultrasonic cavitation bubble or has passed through a small ultrasonic cavitation bubble. At this time, the photodiode array and oscilloscope are replaced with a CMOS array and oscilloscope, and the second laser is turned on. If the interference light received by the CMOS array changes compared to the interference light when the ultrasonic focusing transducer array is not turned on, it is determined that the first laser has passed through a small ultrasonic cavitation bubble. The location and extent of ultrasonic cavitation bubbles are determined by translating or rotating the platform.

2. The method for detecting ultrasonic cavitation using laser interferometry according to claim 1, characterized in that: The waveform of the CMOS array oscilloscope is W = W0cosθ + e + e0, where W0 is the rate of light path deformation caused by light refraction after bubble formation, θ is the initial position, e is the systematic error; since the semiconductor laser has an unstable state of 1-2 ns between startup and stabilization, this error is unavoidable when the cavitation bubble appears less than 30 cm from the light source, and this distance should be left as much as possible when setting the light source; e0 is the random error; waveforms W1, W2, W4, and W5 are obtained by translating or rotating the platform; θ = arctan(W4 - W2) / (W1 - W5), where, W1 = W0cosθ + e + e0, W2=W0cos(θ+90°)+e+e0=-W0sin θ+e+e0, W4=W0cos(θ+270°)+e+e0= W0sin θ+e+e0, W5= W0cos(θ+180°)+e+e0=-W0cos θ+e+e0; W0 = (W4 - W2) / 2sinθ; The θ of the interference light and the deformation rate W0 of the light path can be deduced from the oscilloscope waveforms at various angles. Since R is the bubble radius and λ is the light wavelength in the bubble size parameter a=2πR / λ, and the radius of the tiny bubble is on the order of 10μm-1mm, its scattered light is very weak. The change in optical path is mainly affected by the change in the refracted light path caused by the laser passing through the bubble. Based on the refractive index of the medium and the optical path deformation rate W0, and by measuring the time interval of the changing waveform and the phase change of the changing waveform when the ultrasonic focusing array is working, the size of the laser path in the bubble can be obtained. By comparing the time difference between the waveform change and the trigger signal, the distance between the bubble and the laser source can be obtained.

3. The method for detecting ultrasonic cavitation using laser interferometry according to claim 2, characterized in that: By comparing the difference in waveform W on the photodiode array oscilloscope when the first optical path passes through and does not pass through the ultrasonic cavitation bubble, it can be seen that the laser beam is scattered after passing through a larger ultrasonic cavitation bubble. The waveform of the photodiode array switches to a position deviating from the laser beam path, and the scattered light signal is observed. I(θ',Ψ)=I0λ 2 (i1sin 2 Ψ+i2cos 2 Ψ) / (4π 2 r 2 ); Where Ψ is the angle between the incident photoelectric vector and the observation plane, and i1 and i2 are intensity distribution functions, which are fitted by fixing the angle θ' between the scattered light and the incident light and generating cavitation bubbles of the same size in the water medium with focused ultrasound of the same intensity. When in different media, the bubble size parameters remain unchanged, and their relationship with the refractive index also needs to be refitted. When the cavitation bubble is small, the interference measurement of the first and second optical paths is used. The waveforms W1, W2, W4, and W5 obtained are compared with the waveforms when no cavitation is generated. The waveform difference when the negative pressure peak of the cavitation region is 10 MPa is defined as the reference unit. The intensity of the ultrasonic cavitation bubble on the optical path can be determined by measuring the waveform difference under other conditions.

4. The method for detecting ultrasonic cavitation using laser interferometry according to claim 1, characterized in that: A synchronous time-triggered signal generator simultaneously sends trigger signals to the ultrasonic excitation pulse generator and the laser pulse generator. The waveforms of the interference light receiver of the ultrasonic focusing transducer array when it is activated and when it is not activated are recorded. The time when the waveform changes is taken as the first time. The difference between the first time and the adjacent trigger signal is the time when the ultrasonic cavitation bubble appears.

5. The method for detecting ultrasonic cavitation using laser interferometry according to claim 2, characterized in that: The starting and ending points of the laser beam path when passing through the cavitation bubble are calculated. By changing the position and direction of the laser path's emission point, several sets of points in various directions on the cavitation bubble can be measured. Connecting these points yields the shape of the intersection of the plane parallel to the optical path platform with the cavitation bubble. Rotating the optical path platform then yields the outlines of the planes intersecting the cavitation bubble. Connecting these outlines yields the shape and size of the cavitation bubble.

6. A device for detecting ultrasonic cavitation using laser interferometry, comprising: The system comprises a first laser generator, a second laser generator, a CMOS array and its oscilloscope, a photodiode array and its oscilloscope, an ultrasonic focusing transducer array, a water tank, a light path control box, and a reflector. The first laser generator and the second laser generator are mounted on the platform; this platform is a three-degree-of-freedom moving platform; the CMOS array and its oscilloscope are mounted on the platform; A first laser generator is used to generate a first laser, and a second laser generator is used to generate a second laser. The first laser and the second laser have the same frequency. A photodiode array is used to receive the laser light from the first laser generator and its scattered light. A CMOS array is used to receive the interference light of the first laser and the second laser. The first optical path traversed by the first laser and the second optical path traversed by the second laser have the same path length. The first laser generator, the second laser generator, the CMOS array, and the oscilloscope are fixedly mounted on the platform. An ultrasonic focusing transducer array is installed in a water tank; a platform equipped with a first laser generator, a second laser generator, a CMOS array, and an oscilloscope is located in the water tank, which contains experimental liquid; the platform can move and rotate relative to the water tank. The first laser is used to pass through the focusing area of ​​the ultrasonic focusing transducer array. If the laser intensity received by the photodiode array changes compared to the laser intensity when the ultrasonic focusing transducer array is not activated, it is determined that the first laser has passed through the ultrasonic cavitation bubble. If the laser intensity received by the photodiode array does not change compared to the laser intensity when the ultrasonic focusing transducer array is not activated, it is determined that the first laser has not passed through or has passed through a small ultrasonic cavitation bubble. At this time, the photodiode array and oscilloscope are replaced with a CMOS array and oscilloscope, and the second laser is turned on. If the interference light received by the CMOS array changes compared to the interference light when the ultrasonic focusing transducer array is not activated, it is determined that the first laser has passed through a small ultrasonic cavitation bubble. The location and extent of ultrasonic cavitation bubbles are determined by translating or rotating the platform.

7. The apparatus for detecting ultrasonic cavitation using laser interferometry according to claim 6, characterized in that: The first optical path and the second optical path each include an optical fiber path length control box, which is used to adjust the corresponding optical path so that the first optical path and the second optical path have the same path length.

8. The apparatus for detecting ultrasonic cavitation using laser interferometry according to claim 7, characterized in that: A synchronous time trigger signal generator simultaneously sends trigger signals to the ultrasonic excitation pulse generator and the laser pulse generator. The waveforms of the CMOS array of the ultrasonic focusing transducer array are recorded when the array is activated and when it is not activated. The time when the waveform changes is taken as the first time. The difference between the first time and the adjacent trigger signal is the time when the ultrasonic cavitation bubble appears.

Images