A microfluidic flow field velocimeter and method based on tunable lasers

Abstract

The application discloses a kind of micro flow field velocity measuring device and method based on tunable laser, wherein the velocity measuring device includes tunable laser: including pump light source, plane mirror M1-M4, gain medium layer, frequency doubling crystal, electric rotary displacement table;Micro flow field velocity measuring module: including exit guide pipe, micro flow field simulation glass, constant pressure injection pump, dichroic beam splitter, optical filter, high-power microscope, high-speed camera;Android terminal: including processor and the memory that a plurality of computer instructions are stored.Therein, the velocity measuring method uses the PIV algorithm based on statistical average method to carry out displacement analysis, and the similarity of the particle region in two images is calculated by image template matching, the region with the largest correlation coefficient is regarded as the region reached by particle after a certain time, the displacement of particle is solved, and the velocity distribution of flow field is obtained after the time interval of two images is divided.The device and method make the detection precision improve, and the application scene is more diversified.

Description

Technical Field

[0001] This invention relates to the field of microflow field velocity measurement technology, specifically to a microflow field velocity measurement device and method based on a tunable laser. Background Technology

[0002] Flow field measurement and analysis are widely used in engineering and academic research fields such as aerospace, nuclear thermal energy, chemical metallurgy, hydrogeology, and air pollution. Applications include aircraft shape design, multiphase flow in combustion chambers and reactors, pneumatic and hydraulic transport, and dust separation and collection. Current research on flow field velocimetry technology mainly relies on hydrodynamic and aerodynamic experiments. The main techniques used in these experiments include: the Pitot method, hot-wire hot-film velocimetry, ultrasonic / laser Doppler velocimetry, laser speckle full-field velocimetry, particle tracking velocimetry, and the particle image velocimetry (PIV) technology studied in this invention.

[0003] The main problems with traditional flow field measurement techniques are:

[0004] 1. Contact measurements significantly interfere with the flow field, directly impacting the measurement results. Ideally, velocity measurements should minimize the impact on the flow field. Where possible, experimental environments that allow for interference-free flow visualization should prioritize reproducing the internal flow field profile. Taking the Pitot method and hot-wire / hot-film flowmeters as examples, the probes of both methods affect the internal flow, and contact measurement techniques suffer from difficulties in probe fixation within the flow field, leading to numerous limitations and limited applicability.

[0005] 2. The measurement range is small, and most methods can only measure a single point or a few points. Pitot method and hot wire hot film velocity meter can only perform single-point measurement. Although ultrasonic Doppler velocimeters and laser Doppler velocimeters using ultrasonic waves and lasers can achieve non-contact measurement, they still obtain the velocity distribution of a single point or a few points in the flow field, which cannot meet the need to measure the overall flow field velocity distribution over a large area at the same time.

[0006] PIV technology can solve these problems better. Its basic principle is to disperse appropriate tracer particles in the flow field, illuminate the cross section of the area to be measured with a light source, acquire the exposed particle image through a camera, extract the target image from the obtained image set, and analyze the tracer particles in the image using image processing technology to obtain the particle displacement. After dividing by an extremely short exposure time, the instantaneous velocity inside the flow field within the measurement range can be approximately obtained, thereby realizing large-area, non-contact, instantaneous flow field measurement.

[0007] According to the classification of the International Organization for Fluid Dynamics, flows with characteristic scales between 1 μm and 1 mm are defined as micro-scale flows, and the PIV (Pilot-Induced Vibration) technique applied to micro-flow field measurement is called Micro-PIV (Micro-PIV) technology. Micro-PIV technology places higher demands on the tracer particles seeded in the flow field, requiring more stringent particle selection. On one hand, the particle size used in micro-flow field analysis is generally controlled to be several hundred nanometers. Since the scattered light intensity of ordinary particles of this size is insufficient for imaging requirements, planar laser-induced fluorescence (LAIV) technology is needed for display and measurement. The key to fluorescence tracer methods is selecting a suitable excitation source that matches the fluorescent tracer particles to generate a sufficiently strong fluorescence signal that can be received by the camera. On the other hand, the selection of tracer particles should adhere to basic principles such as not interfering with the flow field and not causing blockage of the flow channels. In current research, different materials of particles are needed as tracer particles for different application scenarios. However, due to the different physicochemical properties of the micro-flow fields being studied, the principles for particle selection also vary. Summary of the Invention

[0008] In view of this, the present invention provides a micro-flow field velocimetry device and method based on a tunable laser. The velocimetry method is executed in a micro-flow field velocimetry device based on a tunable laser, and uses a PIV algorithm based on a statistical averaging method for displacement analysis, including the following steps:

[0009] S1. Obtain particle images using a microflow field velocimetry device based on a tunable laser;

[0010] S2, in Take a point in the particle image at time ( x , y ), take the height and width around this point as follows: wh and ww query window F ( x , y );

[0011] S3, in t +Δ t Searching for particles in the particle image at time t. F ( x , y The most similar windows of the same size are identified as... In the time image, with ( x , y In the query window centered on ), most of the tracer particles have elapsed time. The place reached after moving; and in t +Δ t Points are taken from the time image ( x , y), take the height and width around this point as follows: N × wh and N × ww query window G ( x , y );

[0012] S4, will t Time query window F ( x , y )exist t +Δ t Search window for moments G ( x , y The window is obtained by translating point by point on the surface. G '( x + u , y + v ), u and v Points ( x , y ) in Δ t Horizontal and vertical displacements over time;

[0013] S5, Traversal The similarity of image matching is measured by a normalized correlation function for each pixel in the image at a given time.

[0014] S6. Based on the measured similarity results of image matching, when the correlation coefficient is lower than the set value, a feedback signal is sent to the excitation source of a microflow field velocimetry device based on a tunable laser to adjust the power of the excitation source.

[0015] Furthermore, the query window described in S2 F ( x , y The grayscale function of () is:

[0016]

[0017] The query window described in S3 G ( x , y The grayscale function of () is:

[0018]

[0019] In S4, the search window uses ( x + u , y + v Centered on ), the height and width are respectively wh and ww sub-search window The grayscale function is:

[0020]

[0021] in x , y , wh , ww , m , n , u , v All are non-negative integers.

[0022] Furthermore, F ( x , y )and G '( x + u , y + v The normalized correlation function of ) is:

[0023]

[0024] Furthermore, the PIV algorithm based on Fast Fourier Transform transforms the calculation of spatial domain correlation coefficients into a multiplication calculation formula in the frequency domain:

[0025]

[0026] in F For Fourier transform, F -1 For the inverse Fourier transform, ( ) * To obtain the conjugate, f express t The grayscale function of a query window in a time-lapse image. g express t +Δ t The grayscale function of a search window in a time-lapse image. F ( f )and F ( g ) represents the Fourier transform results of the two.

[0027] The speed measuring device includes: a tunable laser, a microflow field speed measuring module, and an Android terminal;

[0028] The tunable laser includes: a pump source, a plane mirror M1, a gain dielectric layer, a plane mirror M2, a plane mirror M3, a frequency doubling crystal, an electric rotary displacement stage, and a plane mirror M4.

[0029] The electric rotary displacement stage is placed below the frequency doubling crystal. The laser emitted by the pump light source passes sequentially through the plane mirror M1, the gain dielectric layer, the plane mirror M2, the plane mirror M3, the frequency doubling crystal, and the plane mirror M4 to obtain a continuously tunable laser output with a wavelength tuning accuracy of 1nm.

[0030] The microflow field velocity measurement module includes: an ejection conduit, a microflow field simulation slide, a constant pressure injection pump, a dichroic spectrometer, a filter, a high-power microscope, and a high-speed camera;

[0031] The Android terminal includes a processor and a memory storing a number of computer instructions, which, when executed by the processor, implement the steps of the above method.

[0032] The incident light generated by the tunable laser is obliquely incident on the dichroic beam splitter at a 45° angle. The dichroic beam splitter reflects the light at a 45° angle, vertically illuminating the microfluidic field region and exciting the tracer particles to produce a fluorescence reaction, emitting fluorescence of a specific wavelength. Part of the fluorescence is transmitted through the dichroic beam splitter and then passes through a fluorescence filter to filter out most of the non-fluorescent natural light, leaving a fluorescence signal with a narrower spectrum. This signal is then received by a high-speed camera through a microscope. After the high-speed camera records the video data of the flow field motion, the data is transmitted to an Android terminal via a USB data cable.

[0033] Furthermore, the pump source is a pulsed laser.

[0034] Furthermore, the plane mirror M1 is coated with an antireflection film and a high-reflection film on the side near the pump light source, and a gain dielectric layer is spin-coated on the other side to generate fundamental frequency light.

[0035] Furthermore, the plane mirror M2 is a linear polarizer used to convert the fundamental frequency light into linearly polarized light, so that the polarization direction is perpendicular to the incident surface of the frequency doubling crystal.

[0036] Furthermore, the plane mirror M3 is a second harmonic mirror, with an anti-reflection coating and a high-reflection coating on the left side and an anti-reflection coating on the right side.

[0037] Furthermore, the plane mirror M4 is an output mirror, with a high-reflection film and an anti-reflection film coated on the side closest to the crystal, and an anti-reflection film coated on the other side.

[0038] The beneficial effects of the technical solution provided by this invention are:

[0039] (1) In general optical devices, the outgoing and incoming light paths are structurally separate, and the target to be detected can only be located at the intersection of the two light paths. This not only limits the detection range, but also reduces the detection accuracy because the incident and outgoing light surfaces of the flow field are not on the same plane. This device uses a dichroic beam splitter as the core optical device to realize the coaxial multiplexing of the excitation light outgoing light path and the fluorescence incident light path. The excitation light incident light path of the tunable laser and the excitation fluorescence incident light path of the tracer particles in the flow field are independent of each other. The excitation light outgoing light path after reflection by the dichroic beam splitter and the fluorescence outgoing light path after transmission by the dichroic beam splitter are multiplexed into a coaxial light path due to the reflection and transmission of the dichroic beam splitter. This coaxial light path allows the target to be located at any point on the coaxial light path outside the device, and the distance between the target and the device can be varied within a certain range. This makes the application scenarios more flexible, reduces the operation difficulty and complexity of the device, and improves the detection accuracy.

[0040] (2) This device uses a tunable light source at the transmitting end to emit laser light of a specific wavelength, which can emit laser light of multiple wavelengths within a certain band. The excitation light of the corresponding wavelength can be selected according to the fluorescence characteristics of different tracer particles in different flow fields. The receiving end uses a fluorescent filter to filter out fluorescence of a specific wavelength. Different types of fluorescent tracer particles have different excitation wavelengths. By using a tunable laser based on the principle of optical frequency doubling, this device can be widely used in various scenarios that require the use of fluorescent tracers, so that high-speed cameras can record accurate fluorescence signals.

[0041] (3) The analysis software on the Android device is written in the high-performance C++ language to implement the PIV algorithm based on FFT. The processed results are then displayed by a Java program that is well-adapted to the Android device. This leverages the advantages of both languages, resulting in a significant increase in data processing speed and overall software performance. By using the Android terminal to process video data captured by the camera, the traditional computer required for PIV processing devices is eliminated, reducing the overall complexity of the analysis device. It is highly portable, and the device features closed-loop feedback, making the PIV speed measurement device more integrated and applicable to a wider range of scenarios. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the structure of a microflow field velocimetry device based on a tunable laser according to the present invention;

[0043] Figure 2 This invention relates to a tunable laser optical path structure in a microflow field velocimetry device based on a tunable laser. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0045] This invention provides a micro-flow field velocimetry device and method based on a tunable laser. The velocimetry method is executed within a micro-flow field velocimetry device based on a tunable laser. Because the velocity magnitude and direction of each tracer particle in the flow field have significant randomness, and the particles are very small, a large number of tracer particles are needed to accurately reflect the flow field motion. Therefore, it is difficult to find the specific trajectory of a particular particle in the flow field. Traditional displacement calculation methods cannot handle cases where the trajectory is unknown. Therefore, this velocimetry method uses the PIV algorithm based on statistical averaging for displacement analysis. It calculates the similarity of particle regions in two images through image template matching, and considers the region with the highest correlation coefficient as the region reached by the particle after a certain time, thus calculating the particle's displacement. Dividing this displacement by the time interval between the two images yields the velocity distribution of the flow field. The method includes the following steps:

[0046] S1. Obtain particle images using a microflow field velocimetry device based on a tunable laser;

[0047] S2, in Take a point in the particle image at time ( x , y ), take the height and width around this point as follows: wh and ww query window F ( x , y ), query window F ( x , y The grayscale function of () is:

[0048]

[0049] S3, at this point it is necessary to... t +Δ t Searching for particles in the particle image at time t. F ( x , y The most similar windows of the same size are identified as... In the time image, with ( x , y In the query window centered on ) most of the tracer particles have elapsed for time Δ t The place reached after moving. Also in... t +Δ t Points are taken from the time image ( x , y ), take the height and width around this point as follows: N ×wh and N × ww query window G ( x , y ), query window G ( x , y The grayscale function of () is:

[0050]

[0051] S4, will t Time query window F ( x , y )exist t +Δ t Search window for moments G ( x , y The window is obtained by translating point by point on the surface. G '( x + u , y + v ), u and v Points ( x , y ) in Δ t Horizontal and vertical displacement within a time period, in the search window ( x + u , y + v Centered on ), the height and width are respectively wh and ww sub-search window The grayscale function is:

[0052]

[0053] in x , y , wh , ww , m , n , u , v All are non-negative integers.

[0054] S5, Traversal The similarity of image matching is measured by a normalized correlation function for each pixel in the image at a given time. F ( x , y )and G '( x + u , y + v The normalized correlation function of ) is:

[0055]

[0056] When the correlation coefficient R ( u , v When taking the maximum value, consider G '( x + u, y + v ) window is F ( x , y ) After time Δ t The place reached after displacement u and v Points ( x, y )exist Δt The horizontal and vertical displacements within a time interval. From this, we can obtain... t The displacement vector at a certain position in the time-lapse image, traversing t By performing similarity checks on the pixels in the time-lapse image, the displacement vector of the entire observation area can be obtained, thus allowing the calculation of... Δt The velocity field distribution within, when Δt When the velocity field is sufficiently small, it can be considered as a microfluidic field. t The instantaneous velocity distribution at any given moment.

[0057] The PIV algorithm offers high accuracy in displacement calculation and a wide measurable velocity range, but it requires significant computation and is time-consuming when processing large-area, high-resolution images. This velocity measurement method employs the PIV algorithm based on the Fast Fourier Transform (FFT) to transform the calculation of spatial domain correlation coefficients into frequency domain multiplication.

[0058] R = F -1 ( F ( f )×( F ( g )) * )

[0059] in F For Fourier transform, F -1 For the inverse Fourier transform, ( ) * To obtain the conjugate, f express t The grayscale function of a query window in a time-lapse image. g express t + Δt The grayscale function of a search window in a time-lapse image. F ( f) and F ( gThe results are the Fourier transforms of the two. The FFT-based PIV algorithm significantly reduces the computational load required to calculate particle displacement, shortens the time required for PIV software to analyze and process images, and improves the efficiency of the device.

[0060] S6. Based on the measured similarity results of image matching, when the correlation coefficient is lower than the set value, send a feedback signal to the excitation light source to adjust the power of the excitation light source.

[0061] Please refer to Figure 1 , Figure 1 This is a schematic diagram of the structure of a microflow field velocity measurement device based on a tunable laser according to the present invention.

[0062] The speed measuring devices include: a tunable laser, a microflow field speed measuring module, and an Android terminal.

[0063] Please refer to Figure 2 , Figure 2 This invention relates to a tunable laser optical path structure in a microflow field velocimetry device based on a tunable laser.

[0064] The tunable laser includes: a pump source, a plane mirror M1, a gain dielectric layer, a plane mirror M2, a plane mirror M3, a frequency doubling crystal, an electric rotary displacement stage, and a plane mirror M4.

[0065] This device uses a pulsed laser as the pump source and is based on the principle of optical frequency doubling. It selects laser dye as the gain medium of the tunable laser and uses an optical frequency doubling crystal as the laser frequency doubling module. After the pulsed laser emits laser light, it passes through the optical path built by the device to obtain a continuous tunable laser output with a certain wavelength range and a tuning accuracy of 1nm, providing a stable and tunable excitation source for tracer particles in microfluidic fields.

[0066] Plane mirror M1 has an anti-reflection and high-reflection coating on the side closest to the pump source, and a gain medium layer spin-coated on the other side to generate fundamental frequency light. Plane mirror M2 is a linear polarizer used to convert the fundamental frequency light into linearly polarized light, making the polarization direction perpendicular to the incident surface of the frequency doubling crystal. Plane mirror M3 is a second harmonic generation mirror, with an anti-reflection and high-reflection coating on the left side and an anti-reflection coating on the right side. Plane mirror M4 is an output mirror, with a high-reflection and anti-reflection coating on the side closest to the crystal, and an anti-reflection coating on the other side. The high reflectivity of plane mirrors M1 and M4 for the fundamental frequency light allows the fundamental frequency light to repeatedly pass through the frequency doubling crystal, significantly improving the frequency doubling conversion efficiency and fundamental frequency light power density. In addition, the high reflectivity of plane mirror M3 for laser light isolates the frequency-doubled light generated by the frequency doubling crystal from the gain medium, reducing the damage of laser radiation to the gain medium and improving the lifespan of the gain medium layer. Meanwhile, to improve the crystal frequency doubling efficiency, this device employs phase matching technology. It uses an electric rotary displacement stage with a resolution of 0.01° to fine-tune the angle between the crystal optical axis and the linearly polarized light, thereby satisfying the phase matching condition and maximizing the crystal frequency doubling efficiency.

[0067] The microflow field velocity measurement module includes: an ejection conduit, a microflow field simulation slide, a constant pressure injection pump, a dichroic spectrometer, a filter, a high-power microscope, and a high-speed camera.

[0068] An Android terminal includes a processor and a memory storing several computer instructions. When the computer instructions are executed by the processor, they implement the steps of a microflow field velocimetry method based on a tunable laser.

[0069] The incident light generated by the tunable laser is incident at a 45° angle onto a dichroic beam splitter, which reflects the light at the same angle, perpendicularly illuminating the microflow field region. This excites the tracer particles to produce a fluorescence reaction, emitting fluorescence of a specific wavelength. Some of the fluorescence is transmitted through the dichroic beam splitter and then passes through a fluorescence filter, which filters out most of the non-fluorescent natural light, leaving a narrower spectral fluorescence signal. This signal is then captured by a high-speed camera through a microscope. After recording video data of the flow field motion, the high-speed camera transmits the data to an Android terminal via a USB cable. The Android terminal is equipped with self-developed PIV analysis software. After receiving the video data, the software saves it to the terminal's memory. The software can analyze the video image information and, based on the image evaluation results, decide whether to send a feedback signal to the excitation source to adjust its power, thereby improving the quality of the recorded flow field images and enhancing the clarity of the raw flow field analysis data.

[0070] The dichroic beam splitter used is the core component of the coaxial optical path. This device exhibits reflective characteristics in the excitation light band and transmittance characteristics in the fluorescence band generated by the tracer particles. In this embodiment, both the reflectivity and refractive index are above 95%.

[0071] This device employs a coaxial optical path for both transmission and reception, multiplexing the incident and emitted light paths of the tunable laser onto the coaxial optical path. Inside, a glass slide used to simulate the microflow field is positioned at the most suitable observation point within the coaxial optical path. Tracer particles in the flow field are excited by the incident laser, emitting fluorescence. The fluorescence signal is captured by a high-speed camera through the coaxial optical path, thus recording the flow field motion information.

[0072] The velocity measuring device of this invention uses a dichroic beam splitter as its core optical component to achieve coaxial multiplexing of the excitation light output path and the fluorescence incident path, allowing the distance between the target and the device to vary within a certain range. At the transmitting end, a tunable light source emits laser light of a specific wavelength, while at the receiving end, a fluorescence filter filters out fluorescence of a specific wavelength. Different types of fluorescent tracer particles have different excitation wavelengths. By using a tunable laser based on optical frequency doubling, this system can be widely applied to various scenarios requiring fluorescence tracing. The velocity measuring method of this invention innovatively uses an Android terminal as the analysis software platform, ensuring high-performance data processing while enabling faster and more convenient detection of the flow field under test.

[0073] The present invention has been described above with reference to the accompanying drawings. However, the present invention is not superior to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these modifications are within the protection scope of the present invention.

Claims

1. A microflow field velocimetry method based on a tunable laser, implemented in a microflow field velocimetry device based on a tunable laser, employing a PIV algorithm based on statistical averaging for displacement analysis, characterized in that... Includes the following steps: S1. Obtain particle images using a microflow field velocimetry device based on a tunable laser; S2, in t Take a point in the particle image at time ( x , y ), take the height and width around this point as follows: wh and ww query window F ( x , y ); S3, in t +Δ t Searching for particles in the particle image at time t. F ( x , y The most similar windows of the same size are identified as... t In the time image, with ( x , y In the query window centered on ) most of the tracer particles have elapsed for time Δ t The place the vehicle arrived at after moving; And in t +Δ t Points are taken from the time image ( x , y ), take the height and width around this point as follows: N × wh and N × ww query window G ( x , y ); S4, will t Time query window F ( x , y )exist t +Δ t Search window for moments G ( x , y The window is obtained by translating point by point on the surface. G '( x+u , y+v ), u and v Points ( x , y ) in Δ t Horizontal and vertical displacements over time; S5, Traversal t The similarity of image matching is measured by a normalized correlation function for the pixels in the image at each time point. S6. Based on the measured similarity results of image matching, when the correlation coefficient is lower than the set value, a feedback signal is sent to the laser of a microflow field velocimetry device based on a tunable laser to adjust the power of the excitation source.

2. The microflow field velocimetry method based on a tunable laser according to claim 1, characterized in that, The query window described in S2 F ( x , y The grayscale function of () is: The query window described in S3 G ( x , y The grayscale function of () is: In S4, the search window uses ( x+u , y+v Centered on ), the height and width are respectively wh and ww sub-search window G The grayscale function is: in x , y , wh , ww , m , n , u , v All are non-negative integers.

3. The microflow field velocimetry method based on a tunable laser according to claim 1, characterized in that, F ( x , y )and G '( x+u , y+v The normalized correlation function of ) is: 。 4. The microflow field velocimetry method based on a tunable laser according to claim 1, characterized in that, The PIV algorithm based on Fast Fourier Transform transforms the calculation of spatial domain correlation coefficients into a multiplication calculation formula in the frequency domain: in F For Fourier transform, F -1 For the inverse Fourier transform, ( ) * To obtain the conjugate, f express t The grayscale function of a query window in a time-lapse image. g express t +Δ t The grayscale function of a search window in a time-lapse image. F ( f )and F ( g ) represents the Fourier transform results of the two.

5. A microflow field velocimetry device based on a tunable laser, characterized in that, include: Tunable laser, microflow field velocity measurement module, Android terminal; The tunable laser includes: a pump source, a plane mirror M1, a gain dielectric layer, a plane mirror M2, a plane mirror M3, a frequency doubling crystal, an electric rotary displacement stage, and a plane mirror M4. The electric rotary displacement stage is placed below the frequency doubling crystal. The laser emitted by the pump light source passes sequentially through the plane mirror M1, the gain dielectric layer, the plane mirror M2, the plane mirror M3, the frequency doubling crystal, and the plane mirror M4 to obtain a continuously tunable laser output with a wavelength tuning accuracy of 1nm. The microflow field velocity measurement module includes: an ejection guide tube, a microflow field simulation slide, a constant pressure injection pump, a dichroic spectrometer, a filter, a high-power microscope, and a high-speed camera; The Android terminal includes a processor and a memory storing a plurality of computer instructions, which, when executed by the processor, implement the steps of the method according to any one of claims 1 to 4; The incident light generated by the tunable laser is obliquely incident on the dichroic beam splitter at a 45° angle. The dichroic beam splitter reflects the light at a 45° angle, vertically illuminating the microfluidic field region and exciting the tracer particles to produce a fluorescence reaction, emitting fluorescence of a specific wavelength. Part of the fluorescence is transmitted through the dichroic beam splitter and then passes through a fluorescence filter to filter out most of the non-fluorescent natural light, leaving a fluorescence signal with a narrower spectrum. This signal is then received by a high-speed camera through a microscope. After the high-speed camera records the video data of the flow field motion, the data is transmitted to an Android terminal via a USB data cable.

6. The microflow field velocimetry device based on a tunable laser according to claim 5, characterized in that, The pump source is a pulsed laser.

7. A microflow field velocimetry device based on a tunable laser according to claim 6, characterized in that, The plane mirror M1 is coated with an antireflection film and a high-reflection film on one side near the pump light source, and a gain dielectric layer is spin-coated on the other side to generate fundamental frequency light.

8. A microflow field velocimetry device based on a tunable laser according to claim 7, characterized in that, The plane mirror M2 is a linear polarizer used to convert the fundamental frequency light into linearly polarized light, so that the polarization direction is perpendicular to the incident surface of the frequency doubling crystal.

9. A microflow field velocimetry device based on a tunable laser according to claim 8, characterized in that, The plane mirror M3 is a second harmonic mirror, with an anti-reflection coating and a high-reflection coating on the left side and an anti-reflection coating on the right side.

10. A microflow field velocimetry device based on a tunable laser according to claim 9, characterized in that, The plane mirror M4 is an output mirror, with a high-reflection coating and an anti-reflection coating on the side closest to the crystal, and an anti-reflection coating on the other side.

Images