Photon fluid flow velocity and sound velocity measurement method and system combining near-field and far-field measurement

Abstract

The application belongs to the field of optical measurement, and specifically discloses a kind of near far field joint measurement's photon fluid flow velocity and sound velocity measurement method and system, the measurement method includes the following steps: through laser emitting unit produces vortex light beam and irradiates to be measured sample and produces photon fluid, the light beam carrying photon fluid information is separated by light splitting device and is collected near field light spot image and far field point light spot image by first measuring unit and second measuring unit respectively, according to near field light spot image obtains local light intensity and calculates local sound velocity based on local light intensity, nonlinear coefficient and background refractive index, according to far field point light spot obtains centroid shift and determines transverse wave vector based on centroid shift, and then based on transverse wave vector, vortex light beam wavelength and Fourier transform lens focal length calculates two-dimensional flow velocity component.The application can realize single optical path system to the synchronous high-precision, non-interference measurement of photon fluid sound velocity and flow velocity.

Description

Technical Field

[0001] This application belongs to the field of optical measurement, and more specifically, relates to a method and system for measuring photonic fluid velocity and sound velocity through joint near-field and far-field measurement. Background Technology

[0002] Photonic fluids, as a novel type of quantum fluid system, have attracted widespread attention due to their potential applications in nonlinear optics, quantum simulation, and superfluid dynamics. In photonic fluid research, flow velocity and sound velocity are two key parameters that directly reflect the fluid's dynamic behavior and superfluid properties. Accurate measurement of the flow velocity and sound velocity of photonic fluids is crucial for understanding the excitation spectrum and dissipation mechanisms of quantum fluids, as well as for exploring novel optoelectronic devices.

[0003] Currently, common methods for measuring the sound velocity of photonic fluids mainly include time-of-flight methods, interferometry, and analysis methods based on density perturbation propagation. These methods typically require ultrafast detection technology or multi-frame image acquisition to extract sound velocity information by tracking the propagation distance and time of perturbation wave packets. Flow velocity measurements, on the other hand, often rely on Doppler frequency shift methods or particle tracing methods, obtaining flow velocity data by analyzing the frequency changes of a light beam or the trajectories of traced particles.

[0004] However, existing technologies have the following shortcomings: Firstly, the measurement of sound velocity and flow velocity often requires two independent optical path systems, leading to system complexity and cumbersome operation. Furthermore, the errors introduced between different systems are difficult to calibrate uniformly, limiting further improvements in measurement accuracy. Secondly, traditional methods have high requirements for the coherence and stability of the light source, making them susceptible to environmental vibrations and background noise interference, thus limiting measurement accuracy. In addition, some methods require the application of external probes or markers to the photonic fluid, which may interfere with the fluid's own state and affect the accuracy of the measurement results.

[0005] Therefore, how to achieve synchronous, high-precision, and interference-free measurement of the sound velocity and flow velocity of photonic fluids using a single optical path system is a problem that urgently needs to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this application is to provide a method and system for measuring the velocity and sound speed of photonic fluids in both near and far fields, which can achieve synchronous, high-precision, and interference-free measurement of the velocity and sound speed of photonic fluids using a single optical path system.

[0007] To achieve the above objectives, in a first aspect, this application provides a method for measuring photonic fluid velocity and sound velocity through joint near-field and far-field measurements, comprising the following steps: S10, a vortex beam is generated by the laser emitting unit to irradiate the sample to be tested. The vortex beam interacts with the sample to be tested to generate photonic fluid. The beam carrying the photonic fluid information is split into a first beam and a second beam by a beam splitter after passing through a 4f system. The near-field spot image of the first beam is acquired, and the far-field spot image of the second beam is acquired after being filtered through a pinhole and passed through a Fourier transform lens. S20, obtain the local light intensity based on the near-field light spot image, and calculate the local sound velocity of the photonic fluid based on the local light intensity, the nonlinear coefficient of the sample and the background refractive index. S30, obtain the centroid offset based on the far-field spot, determine the transverse wave vector based on the centroid offset, and calculate the two-dimensional velocity component of the photonic fluid based on the transverse wave vector, the wavelength of the vortex beam, and the focal length of the Fourier transform lens.

[0008] As a further preferred embodiment, the laser emitting unit includes a laser emitter, a collimator and beam expander, a reflector M1, a spatial light modulator, a reflector M2, a reflector M3, and a reflector M4; The laser emitter generates a fundamental Gaussian beam and emits it to the collimating beam expander; the collimating beam expander expands the fundamental Gaussian beam and emits the expanded beam to the reflector M1; the reflector M1 reflects the expanded beam to the spatial light modulator; the spatial light modulator loads a hologram to modulate the laser beam into the vortex beam; the reflector M2 reflects the vortex beam to the sample under test; the reflectors M3 and M4 are used to collimate the outgoing light path of the vortex beam.

[0009] As a further preferred embodiment, the sample to be tested is an azo-doped liquid crystal; the azo-doped liquid crystal interacts with the vortex beam to generate a thermo-optical nonlinear effect and a photoinduced isomerism effect, forming the photonic fluid.

[0010] As a further preferred embodiment, the 4f system includes two plano-convex lenses PCX1 and PCX2 with the same focal length; the 4f system is used to ensure that the light beam emitted from the sample under test arrives at the beam splitter in parallel.

[0011] As a further preferred embodiment, the near-field spot image of the first beam after imaging is acquired by the imaging device CCD1; the spot image of the second beam formed in the far field after being filtered through a pinhole and passed through a Fourier transform lens is acquired by: the pinhole isolating the local spot and guiding the local spot to the Fourier transform lens; the Fourier transform lens performs a Fourier transform on the local spot, forming the far-field spatial distribution of the local spot on the back focal plane of the Fourier transform lens; and then the spot image of the far-field spatial distribution is acquired by the imaging device CCD2.

[0012] As a further preferred embodiment, an electric three-dimensional displacement stage is used to control the pinhole to scan point by point along the -y direction, and the unidirectional displacement accuracy of the electric three-dimensional displacement stage is 3 micrometers; the far-field spot images of the pinhole collected at each scanning position are obtained by recording video and extracting key frames.

[0013] As a further preferred embodiment, the local light intensity is obtained through the following steps: converting the near-field spot image into a grayscale image, and integrating the grayscale image to obtain the total grayscale value. ; Calculate the gray-level integral of a local region on the image. The size of the localized area is the same as the area of ​​the imaging region of the pinhole in the image, and the localized grayscale ratio is... The total power of the near-field spot was measured using a power meter under the same optical path. The power of the local light spot is The local light intensity is , This represents the effective area for pinhole screening.

[0014] As a further preferred embodiment, the formula for calculating the local sound speed is:

[0015] in, c The speed of light; The nonlinear coefficient of the sample under test; The local light intensity; The background refractive index is given.

[0016] As a further preferred embodiment, the formula for calculating the transverse wave vector is:

[0017] Where, Δ x and Δ y These are the components of the centroid offset in the x-axis and y-axis directions, respectively. λ The wavelength of the vortex beam; f Let be the focal length of the Fourier transform lens; The formula for calculating the two-dimensional velocity component is:

[0018] in, ; c The speed of light; The background refractive index is given.

[0019] Secondly, this application provides a photonic fluid velocity and sound velocity measurement system for joint near-field and far-field measurements, used to perform the method as described in any one of the above statements, comprising: A laser emitting unit is used to generate a vortex beam and emit the vortex beam toward the sample to be tested; The sample to be tested is used to interact with the vortex beam to generate a photonic fluid; The 4f system is set in the output light path of the sample to be tested, and is used to make the light beam emitted from the sample to be tested reach the beam splitter in parallel. A beam splitter is disposed on the output optical path of the 4f system to split the beam into a first beam and a second beam. The first measurement unit is set on the first outgoing optical path of the beam splitter and is used to acquire the near-field spot image after the first beam is imaged. The second measurement unit is set on the second outgoing light path of the beam splitter and includes a pinhole, a Fourier transform lens and an imaging device, used to acquire the spot image formed in the far field after the second beam is filtered through the pinhole and passed through the Fourier transform lens. The computing unit is connected to the first measurement unit and the second measurement unit respectively, and is used to calculate the local sound velocity of the photonic fluid based on the near-field spot image, and to calculate the two-dimensional velocity component of the photonic fluid based on the far-field spot image.

[0020] This application offers the following advantages: Using the same optical path system, a beam carrying photonic fluid information, after the vortex beam interacts with the sample, is split into a first beam and a second beam using a beam splitter. Near-field and far-field spot images are acquired separately, allowing the near-field information required for sound velocity measurement and the far-field information required for flow velocity measurement to be acquired simultaneously within the same optical path architecture, eliminating the need for two independent optical path systems. Specifically, the near-field spot image is used to extract local light intensity and calculate the local sound velocity, while the far-field spot image is used to obtain the centroid offset, determine the transverse wave vector, and calculate the two-dimensional flow velocity components. This method achieves joint near-field and far-field measurements through the same optical path system, simultaneously obtaining the sound velocity and two-dimensional flow velocity of the photonic fluid. The method simplifies the system structure and avoids the problem of inconsistent calibration of errors between different systems, thus improving measurement accuracy. Furthermore, by using the image of the emitted light spot after the vortex beam passes through the sample as an information carrier, it directly analyzes the sound velocity and flow velocity information from the light spot image. This eliminates the need to rely on the coherence and stability of the light source to ensure measurement accuracy. Instead, it calculates the required physical quantities by acquiring the light spot image and extracting its intensity distribution and centroid position information, thereby reducing sensitivity to environmental vibrations and background noise and achieving high-precision measurement. Moreover, it eliminates the need for external probes or markers on the photonic fluid, avoiding interference from external probes on the fluid state and ensuring the authenticity of the measurement results. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the photonic fluid velocity and sound velocity measurement system provided in the embodiments of this application; Figure 2 This is a near-field spot image acquired according to an embodiment of this application; Figure 3 These are curves showing the radial velocity, total velocity, and sound velocity of the photonic fluid as a function of radius, provided in the embodiments of this application. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] To address the technical problems of existing technologies where flow velocity and sound velocity measurements require time-sharing or separate system operations, are cumbersome, are susceptible to environmental interference in measurement accuracy, and where external probes may affect the true state of the fluid, this application proposes a method that simultaneously acquires near-field and far-field images of the interaction between a vortex beam and the sample under test (such as azo-doped liquid crystal) using the same optical path system. Sound velocity and flow velocity information are then extracted separately, enabling rapid, non-contact, and high-precision synchronous measurement. This simplifies the system structure and improves the accuracy and reliability of the measurement. Traditional samples to be measured include materials with thermo-optical nonlinear properties, such as azo-doped liquid crystals and mixtures of nanoscale graphene powder and graphene.

[0024] This application employs a strategy of joint measurement of near-field spot and far-field spot. The local light intensity is extracted using the intensity distribution of the near-field spot, and the local sound velocity of the photonic fluid is calculated. The two-dimensional component of the transverse wave vector is extracted using the centroid offset of the far-field spot, thereby obtaining the two-dimensional velocity distribution of the photonic fluid (including radial and tangential components).

[0025] This application proposes a two-dimensional photonic fluid velocity and sound velocity measurement system based on near-field and far-field joint measurement, comprising: a laser emitting unit, a sample to be measured, a 4f system, a beam splitting device, a first measurement unit, a second measurement unit, and a calculation unit; A laser emitting unit is used to generate a vortex beam and emit the vortex beam toward the sample to be tested. The sample under test is used to interact with the vortex beam to generate nonlinear optical effects and photoinduced isomerism, forming a photonic fluid. The 4f system is used to ensure that the beam emitted from the sample arrives at the beam splitter in parallel. The beam splitter is used to split the vortex beam into two beams, which are then guided to the first measurement unit and the second measurement unit, respectively. The first measurement unit is used to acquire the near-field light spot intensity distribution after nonlinear evolution in real time, and to measure the sound velocity of the photonic fluid accordingly. The second measurement unit is used to acquire far-field spot light and measure the two-dimensional velocity components of the photonic fluid accordingly. The computing unit is connected to the first measurement unit and the second measurement unit respectively, and is used to calculate the local sound velocity of the photonic fluid based on the near-field spot image, and to calculate the two-dimensional velocity component of the photonic fluid based on the far-field spot image.

[0026] Optionally, the laser emitting unit includes a laser emitter, a collimator and beam expander, a reflector M1, a spatial light modulator, and a reflector M2.

[0027] A laser emitter is used to generate a fundamental Gaussian beam and emit the fundamental Gaussian beam to a collimating beam expander; A collimating beam expander is used to expand the fundamental mode Gaussian beam and then emit the expanded fundamental mode Gaussian beam to the first reflecting mirror. Mirror M1 is used to reflect the expanded fundamental mode Gaussian beam to the spatial light modulator; Spatial light modulators are used to load holograms of a specific phase to modulate laser beams into desired vortex beams. The reflector M2 is used to reflect the vortex beam onto the sample to be tested.

[0028] Optionally, the laser emitting unit also includes reflector M3 and reflector M4; Reflectors M3 and M4 are used to straighten the outgoing optical path of the collimated vortex beam.

[0029] Optionally, the incident angle of the expanded fundamental Gaussian beam onto the spatial light modulator is less than 15 degrees.

[0030] Optionally, the sample to be tested is an azo-doped liquid crystal. Azo-doped liquid crystals are used to interact with vortex beams to generate photonic fluids.

[0031] Optionally, the 4f system includes two plano-convex lenses PCX1 and PCX2 with the same focal length, which are used to make the beam emitted from the sample arrive at the beam splitter in parallel. Optionally, the first measurement unit includes an imaging device CCD1. The imaging device CCD1 is used to acquire near-field spot images of the vortex beam.

[0032] Optionally, the second measuring unit includes a pinhole, a lens PCX3, and an imaging device CCD2.

[0033] The pinhole is used to isolate the local light spot and emit the local light spot to the lens PCX3; The PCX3 lens is used to perform Fourier transform on the local spot to form the far-field spatial distribution of the local spot on its back focal plane. The imaging device CCD2 is used to acquire images of light spots distributed in the far field.

[0034] Optionally, the computing unit includes a computer with data processing, network communication, and program execution functions. The computer is connected to imaging devices CCD1 and CCD2 respectively, and is used to calculate the local sound velocity of the photonic fluid based on the near-field spot image, and to calculate the two-dimensional velocity components of the photonic fluid based on the far-field spot image.

[0035] Furthermore, to achieve the above objectives, this application also proposes a two-dimensional photonic fluid velocity and sound velocity measurement method based on near-field and far-field joint measurement. This method is applied to the aforementioned photonic fluid velocity and sound velocity measurement system, and includes: Construct the measurement optical path; Acquire images of the near-field and far-field spot of the vortex beam in the measurement optical path; The two-dimensional velocity components and sound speed of the photonic fluid are calculated based on the collected light spot images.

[0036] This application modulates the fundamental mode Gaussian beam into a vortex beam using a laser emission unit and emits the vortex beam to the sample to be tested. After passing through a 4f system, the beam reaches a beam splitter and is then split into two beams, which are guided to the first measurement unit and the second measurement unit, respectively.

[0037] In one embodiment, the technical solution to achieve the above objective can be as follows: This embodiment provides a two-dimensional photonic fluid velocity and sound velocity measurement system based on near-field and far-field joint measurement, the structure of which is as follows. Figure 1 As shown, the photonic fluid velocity and sound velocity measurement system includes: a laser emitting unit, a sample to be measured, a 4f system, a spectrometer, a first measurement unit, a second measurement unit, and a calculation unit.

[0038] The laser emitting unit generates a vortex beam and emits it onto the sample under test. The laser emitting unit includes a laser emitter, a collimating beam expander, a reflector M1, a spatial light modulator, and a reflector M2. The laser emitter generates a fundamental Gaussian beam and emits it to the collimating beam expander. After expansion, the fundamental Gaussian beam passes through reflector M1 and is incident on the spatial light modulator. The spatial light modulator loads a hologram with a specific phase, modulating the laser beam into the desired vortex beam. The vortex beam is reflected by reflector M2 onto the sample under test. Reflectors M3 and M4 are also placed between reflector M2 and the sample under test to better collimate the outgoing light path of the vortex beam. To improve the modulation efficiency of the spatial light modulator, the incident angle of the fundamental Gaussian beam onto the spatial light modulator should be less than 15 degrees.

[0039] The sample to be tested is an azo-doped liquid crystal, which has thermo-optical nonlinearity and photo-induced isomerism, and generates photonic fluid after interacting with a vortex beam.

[0040] The 4f system includes two plano-convex lenses PCX1 and PCX2 with the same focal length, used to ensure that the beam emitted from the sample arrives at the beam splitter in parallel.

[0041] The beam splitter is a beam splitter prism BS, which is used to split the vortex beam into two beams, which are then guided to the first measurement unit and the second measurement unit, respectively.

[0042] The first measurement unit is used to acquire the near-field beam intensity distribution after nonlinear evolution in real time, and to measure the sound velocity of the photonic fluid accordingly. The first measurement unit is an imaging device CCD1, used to acquire near-field beam images of the vortex beam, such as... Figure 2 As shown.

[0043] The second measurement unit is used to acquire a far-field spot and measure the velocity of the photon fluid accordingly. The second measurement unit includes a pinhole, a lens PCX3, and an imaging device CCD2. The pinhole isolates a localized spot and guides it to the lens PCX3. The lens PCX3 performs a Fourier transform on the localized spot to obtain its far-field spatial distribution on its back focal plane. The imaging device CCD2 acquires an image of the far-field spot of the vortex beam.

[0044] The computing unit is connected to imaging devices CCD1 and CCD2 respectively, and is used to calculate the local sound velocity of the photonic fluid based on the near-field spot image, and to calculate the two-dimensional velocity component of the photonic fluid based on the far-field spot image.

[0045] This embodiment also provides a method for measuring photonic fluid velocity and sound velocity based on near-field and far-field joint measurement, including: To construct the measurement optical path, this method also requires a vortex beam velocity and sound velocity measurement device with data processing, network communication, and program execution functions.

[0046] The system acquires near-field and far-field spot images of the vortex beam in the measurement optical path. The acquisition process for the far-field spot is as follows: first, a local spot is isolated through a pinhole, then Fourier transform is performed through the lens PCX3 to form the far-field spatial distribution of the local spot on the back focal plane, and finally, it is acquired by the imaging device CCD2.

[0047] The velocity of the photonic fluid and the speed of sound are calculated based on the collected light spot images.

[0048] (1) Measurement of sound speed The local speed of sound in the photonic fluid is:

[0049] in, W is the nonlinear coefficient of the sample; The light intensity of the local spot after pinhole isolation is obtained by processing the near-field spot image. The background refractive index is given.

[0050] First, the near-field spot image acquired by the CCD1 imaging device is converted into a grayscale image. Then, the grayscale image is integrated to obtain the total grayscale value. Then calculate the gray-level integral of the local region on the image. The size of the localized area is the same as the area of ​​the pinhole's image region. Therefore, the local grayscale percentage is... .

[0051] Then, a power meter was used to measure the total power of the near-field spot under the same optical path. The power of the local light spot is The light intensity of the local light spot is , The effective area for pinhole screening. The obtained light intensity... Substituting these values ​​into the formula for calculating the local speed of sound, we can obtain the local speed of sound of the photonic fluid. As the radius changes.

[0052] (2) Flow velocity measurement The core of flow velocity measurement is to convert the local flow velocity into a local phase gradient (i.e., a local transverse wave vector), and then use the centroid shift of the point spot on the Fourier surface to calibrate the wave vector. We use a motorized three-dimensional high-precision displacement stage to control the movement of the pinhole. This stage can move along the x, y, and z directions, where the z direction is the direction of light field propagation, and the unidirectional displacement accuracy is 3 µm. The pinhole is fixed on the displacement stage, and the stage is controlled to perform high-precision point-by-point scanning of the pinhole along the -y direction. A plano-convex lens PCX3 with a focal length of 50.8 mm is placed behind the pinhole. Fourier transform is performed on the local spot isolated by the pinhole to form the far-field spatial distribution of the local spot on its back focal plane, which is finally acquired by the imaging device CCD2.

[0053] The single-movement error of the 3D displacement stage is 3 µm. Manually capturing images after each pinhole movement will accumulate errors. Therefore, recording video and extracting keyframes can reduce the errors caused by manual image capture and improve experimental efficiency. Next, the obtained spot images need preprocessing. First, all spot images are converted into grayscale intensity distribution maps; then, background noise is subtracted using dark-field images, and Gaussian filtering is applied for smoothing and noise reduction to weaken the interference of speckle and random noise on localization.

[0054] The centroid coordinates of each spot were obtained by analyzing the acquired far-field spot. and the centroid position of the center spot on the scanning path Then the centroid offset is The local transverse wave vector is:

[0055] in, Where is the wavelength of the incident light. Let be the focal length of the plano-convex lens PCX3. The two-dimensional velocity components of the photonic fluid can be obtained from the transverse wave vector:

[0056] in, .

[0057] Radial flow velocity, Let be the tangential velocity, and the total velocity be... Therefore, the radial velocity and total velocity of the photonic fluid can be obtained as a function of radius. The curves showing the changes in sound velocity, radial velocity, and total velocity of the photonic fluid as a function of radius are shown below. Figure 3 As shown.

[0058] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for measuring photonic fluid velocity and sound velocity through combined near-field and far-field measurements, characterized in that, Includes the following steps: S10, a vortex beam is generated by the laser emitting unit to irradiate the sample to be tested. The vortex beam interacts with the sample to be tested to generate photonic fluid. The beam carrying the photonic fluid information is split into a first beam and a second beam by a beam splitter after passing through a 4f system. The near-field spot image of the first beam is acquired, and the far-field spot image of the second beam is acquired after being filtered through a pinhole and passed through a Fourier transform lens. S20, obtain the local light intensity based on the near-field light spot image, and calculate the local sound velocity of the photonic fluid based on the local light intensity, the nonlinear coefficient of the sample and the background refractive index. S30, obtain the centroid offset based on the far-field spot, determine the transverse wave vector based on the centroid offset, and calculate the two-dimensional velocity component of the photonic fluid based on the transverse wave vector, the wavelength of the vortex beam, and the focal length of the Fourier transform lens.

2. The method for measuring photonic fluid velocity and sound velocity through near-field and far-field joint measurement as described in claim 1, characterized in that, The laser emitting unit includes a laser emitter, a collimator and beam expander, a reflector M1, a spatial light modulator, a reflector M2, a reflector M3, and a reflector M4; The laser emitter generates a fundamental Gaussian beam and emits it to the collimating beam expander; the collimating beam expander expands the fundamental Gaussian beam and emits the expanded beam to the reflector M1; the reflector M1 reflects the expanded beam to the spatial light modulator; the spatial light modulator loads a hologram to modulate the laser beam into the vortex beam; the reflector M2 reflects the vortex beam to the sample under test; the reflectors M3 and M4 are used to collimate the outgoing light path of the vortex beam.

3. The method for measuring photonic fluid velocity and sound velocity through combined near-field and far-field measurements as described in claim 1, characterized in that, The sample to be tested is an azo-doped liquid crystal; the azo-doped liquid crystal interacts with the vortex beam to generate a thermo-optical nonlinear effect and a photoinduced isomerism effect, forming the photonic fluid.

4. The method for measuring photonic fluid velocity and sound velocity through combined near-field and far-field measurements as described in claim 1, characterized in that, The 4f system includes two plano-convex lenses PCX1 and PCX2 with the same focal length; the 4f system is used to ensure that the light beam emitted from the sample under test arrives at the beam splitter in parallel.

5. The method for measuring photonic fluid velocity and sound velocity through combined near-field and far-field measurements as described in claim 1, characterized in that, The near-field spot image of the first beam after imaging is acquired by the imaging device CCD1; the far-field spot image formed by the second beam after being filtered through a pinhole and passed through a Fourier transform lens is acquired by: the pinhole isolating the local spot and guiding the local spot to the Fourier transform lens; the Fourier transform lens performs a Fourier transform on the local spot, forming a far-field spatial distribution of the local spot on the back focal plane of the Fourier transform lens; and then the far-field spatial distribution of the spot image is acquired by the imaging device CCD2.

6. The method for measuring photonic fluid velocity and sound velocity through near-field and far-field joint measurement as described in claim 1, characterized in that, An electric three-dimensional displacement stage is used to control the pinhole to scan point by point along the -y direction. The unidirectional displacement accuracy of the electric three-dimensional displacement stage is 3 micrometers. The far-field spot images of the pinhole at each scanning position are obtained by recording video and extracting key frames.

7. The method for measuring photonic fluid velocity and sound velocity through near-field and far-field joint measurement as described in claim 1, characterized in that, The local light intensity is obtained through the following steps: converting the near-field spot image into a grayscale image, and integrating the grayscale image to obtain the total grayscale value. ; Calculate the gray-level integral of a local region on the image. The size of the localized area is the same as the area of ​​the imaging region of the pinhole in the image, and the localized grayscale ratio is... The total power of the near-field spot was measured using a power meter under the same optical path. The power of the local light spot is The local light intensity is , This represents the effective area for pinhole screening.

8. The method for measuring photonic fluid velocity and sound velocity through combined near-field and far-field measurements as described in claim 1, characterized in that, The formula for calculating the local sound speed is as follows: in, c The speed of light; The nonlinear coefficient of the sample under test; The local light intensity; The background refractive index is given.

9. The method for measuring photonic fluid velocity and sound velocity through near-field and far-field joint measurement as described in claim 1, characterized in that, The formula for calculating the transverse wave vector is: Where, Δ x and Δ y These are the components of the centroid offset in the x-axis and y-axis directions, respectively. λ The wavelength of the vortex beam; f Let be the focal length of the Fourier transform lens; The formula for calculating the two-dimensional velocity component is: in, ; c The speed of light; The background refractive index is given.

10. A photonic fluid velocity and sound velocity measurement system for joint near-field and far-field measurements, used to perform the method as described in any one of claims 1 to 9, characterized in that, include: A laser emitting unit is used to generate a vortex beam and emit the vortex beam toward the sample to be tested; The sample to be tested is used to interact with the vortex beam to generate a photonic fluid; The 4f system is set in the output light path of the sample to be tested, and is used to make the light beam emitted from the sample to be tested reach the beam splitter in parallel. A beam splitter is disposed on the output optical path of the 4f system to split the beam into a first beam and a second beam. The first measurement unit is set on the first outgoing optical path of the beam splitter and is used to acquire the near-field spot image after the first beam is imaged. The second measurement unit is set on the second outgoing light path of the beam splitter and includes a pinhole, a Fourier transform lens and an imaging device, used to acquire the spot image formed in the far field after the second beam is filtered through the pinhole and passed through the Fourier transform lens. The computing unit is connected to the first measurement unit and the second measurement unit respectively, and is used to calculate the local sound velocity of the photonic fluid based on the near-field spot image, and to calculate the two-dimensional velocity component of the photonic fluid based on the far-field spot image.

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