Femtosecond laser molecular marker-based flow field velocity and pressure measuring device and method

Abstract

The invention provides a device and a method for simultaneously measuring the velocity and the pressure of a flow field based on femtosecond laser molecular markers. The measuring device comprises a femtosecond laser module, a flow field module, an optical focusing module, a signal acquisition module and a data processing module, the optical focusing module focuses the femtosecond laser in the ultraviolet band into a femtosecond filament, and the center of a focus point of the femtosecond filament is located at the center of the flow field to be measured; introducing the mixed gas into the spray pipe to generate a to-be-measured flow field of the mixed gas; the signal acquisition module acquires speed and pressure signals; and the data processing module receives the speed and pressure sensing signals, executes calculation and outputs flow field speed and pressure measurement results obtained through calculation. Multi-parameter synchronous measurement is adopted, non-intrusive measurement of the flow field speed and pressure can be achieved at the same time by analyzing the luminescence characteristics of carbon-nitrogen free radicals, particles or probes do not need to be added, and interference to the flow field is avoided.

Description

Technical Field

[0001] This invention belongs to the field of laser measurement technology and relates to a device and method for measuring flow velocity and pressure based on femtosecond laser molecular labeling. Background Technology

[0002] In aerospace, energy, and power fields, flow velocity and pressure are key parameters for characterizing the physical properties of flow fields and optimizing equipment performance. For example, flow field parameter measurements in supersonic wind tunnels directly affect the accuracy of aircraft aerodynamic design, and monitoring of rocket engine exhaust flow field parameters is crucial for evaluating propulsion system efficiency. Traditional flow velocity measurement methods include pitot tubes and hot-wire anemometers, while flow pressure measurement techniques mostly utilize contact measurement methods such as pressure sensors. Traditional contact measurements inevitably interfere with the flow field, affecting in-situ flow field measurement and accuracy, and their response speed is somewhat limited. Optical, especially laser-based, non-invasive measurement offers an excellent technical solution to address these issues. Optical pressure sensors include various types: intensity-based pressure sensors, polarized light pressure sensors, and phase-based (interferometric) pressure sensors. Currently, optical pressure sensors are rapidly developing due to their advantages such as radiation resistance, electromagnetic interference resistance, small size, high sensitivity, and high accuracy, making them suitable for applications in extreme environments with high radiation and high temperatures, such as space and deserts. However, all of the above pressure sensors are designed for measuring pressure in closed environments. In recent years, femtosecond lasers have developed rapidly, and their filamentation characteristics caused by the self-focusing effect have become a major research focus. The filament shape of femtosecond lasers is related to the pressure in the measured environment, which provides a simpler and more accurate method for pressure measurement and holds promise for measuring gas pressure in open environments.

[0003] Chinese patent publication CN109580080A discloses a device and method for measuring flow field pressure based on femtosecond laser filamentation. The device includes a femtosecond laser, an ICCD camera, a focusing lens, a quartz tube, and a computer. The focusing lens is placed in front of the quartz tube, with its focal point located inside the quartz tube. The laser emitted from the femtosecond laser is focused by the focusing lens and then incident on the quartz tube. The quartz tube is closed at both ends and has adjustable pressure. An inlet and an outlet are provided on the cylindrical surface of the quartz tube. The ICCD camera is placed on one side of the quartz tube and perpendicular to the femtosecond laser emitted into the quartz tube. It is used to capture and image the fluorescence signal generated inside the quartz tube. The computer is used to run corresponding software to process the data and finally obtain the pressure inside the quartz tube. This invention can achieve non-invasive measurement of gas pressure in a quasi-static environment.

[0004] Currently, commonly used techniques for flow velocity measurement include particle image velocimetry (PIV), laser Doppler velocimetry (LDV), and tunable semiconductor laser absorption spectroscopy (TDLAS). Common pressure measurement techniques include laser interferometry and coherent anti-Stokes Raman spectroscopy (CARS). These existing techniques all have certain limitations: Particle image velocimetry (PIV) requires the addition of particles to the flow field, and the following behavior of these particles affects measurement accuracy; it also cannot simultaneously measure pressure. Laser Doppler velocimetry (LDV) can only perform point measurements, making it difficult to obtain spatial distribution information of the flow field. Tunable semiconductor laser absorption spectroscopy (TDLAS) can measure flow velocity, but it is a line-of-sight measurement technique with limited spatial resolution. While commonly used pressure measurement techniques, including laser interferometry and coherent anti-Stokes Raman spectroscopy (CARS), can simultaneously measure temperature and pressure, their complex optical systems require precise spatiotemporal alignment of multiple laser beams, limiting their applicability in the high-noise environment of wind tunnels, and they cannot directly and synchronously measure velocity.

[0005] In summary, current techniques for measuring gas flow velocity and pressure have limitations and shortcomings. There is an urgent need for a measurement method and equipment capable of simultaneously measuring flow velocity and pressure. Summary of the Invention

[0006] To address the aforementioned technical problems, the first aspect of this invention proposes a device for simultaneously measuring flow velocity and pressure based on femtosecond laser molecular labeling. The measuring device includes a femtosecond laser module, a flow field module, an optical focusing module, a signal acquisition module, and a data processing module. The femtosecond laser module is used to generate femtosecond lasers in the ultraviolet band; The optical focusing module focuses the femtosecond laser into a femtosecond filament and keeps the focal point of the femtosecond filament at the center of the flow field to be measured. The flow field module includes a nozzle made of a material transparent to femtosecond lasers. The mixed gas to be measured is introduced into the nozzle to generate the flow field to be measured for the mixed gas. The signal acquisition module includes: a speed signal acquisition device and a pressure signal acquisition device; The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, performs calculations, and outputs the calculated flow field velocity and pressure measurement results.

[0007] The measuring device as described in the first aspect of the present invention, wherein the femtosecond laser module comprises: a femtosecond laser, a laser frequency doubling unit, and a laser attenuator disposed after the laser frequency doubling unit, wherein the femtosecond laser generates an ultrashort pulse laser with a femtosecond pulse width, the laser frequency doubling unit is disposed on the transmission path of the femtosecond ultrashort pulse laser, and the aperture of the laser frequency doubling unit is greater than or equal to the diameter of the incident femtosecond ultrashort pulse laser beam; The laser frequency doubling unit performs frequency doubling on the femtosecond-level ultrashort pulse laser and outputs a frequency-doubled ultraviolet-band femtosecond-level ultrashort pulse laser. The ultraviolet-band femtosecond-level ultrashort pulse laser passes through a laser attenuator, and the output laser intensity can be adjusted by the laser attenuator.

[0008] The measuring device as described in the first aspect of the present invention, wherein the femtosecond laser is a Ti:sapphire femtosecond laser, and the Ti:sapphire femtosecond laser outputs a femtosecond laser with a center wavelength of 800 nm; The laser frequency doubling unit is a solid-state third frequency multiplier, which up-converts a femtosecond laser with a center wavelength of 800 nm into a femtosecond pulse laser with a center wavelength of 267 nm in the ultraviolet band.

[0009] The measuring apparatus as described in the first aspect of the present invention, wherein the mixed gas to be measured is generated by mixing nitrogen and methane of a predetermined concentration.

[0010] As described in the first aspect of the present invention, the pressure signal acquisition device includes an imaging spectrometer and a first ICCD camera; the imaging spectrometer and the first ICCD camera are used to receive the short-lifetime emission signals of carbon and nitrogen free radicals after the mixed gas is irradiated by a laser. The light incident slit of the imaging spectrometer is arranged in a direction parallel to the propagation direction of the femtosecond filament; The first ICCD camera is coupled to the imaging spectrometer to capture and collect the short-lifetime emission signals of carbon and nitrogen free radicals that are incident on the light incident slit of the imaging spectrometer after the mixed gas is irradiated by laser. The velocity signal acquisition device includes a second ICCD camera, the optical axis of which is set perpendicular to the flow direction of the mixed gas and the propagation direction of the femtosecond pulse laser, for capturing long-lifetime emission signals of carbon and nitrogen free radicals.

[0011] As described in the first aspect of the present invention, the optical focusing module includes a spherical lens or a concave mirror, wherein the focal point of the spherical lens or the concave mirror is located at the center of the flow field to be measured. When a spherical lens is used to focus a femtosecond laser, the two mirror surfaces of the spherical lens are coated with an antireflective coating whose center wavelength is located at the center wavelength of the ultraviolet laser, and the transmittance of the antireflective coating is ≥95%. When a concave mirror is used to focus a femtosecond laser, an anti-reflective coating is deposited on the reflective surface with a center wavelength located at the center wavelength of the ultraviolet laser, and the reflectivity of the anti-reflective coating is ≥99%.

[0012] A second aspect of the present invention provides a measurement method for the simultaneous measurement device for flow field velocity and pressure based on femtosecond laser molecular labeling as described in any one of the preceding claims, the measurement method comprising the following steps: Step 1: Add a predetermined proportion of methane gas to the nitrogen gas to be measured in the injection flow field module, and inject the mixture of nitrogen gas and methane gas into the nozzle. Step 2: Focus a femtosecond pulsed laser with a specified center wavelength and pulse width onto the nozzle to form a femtosecond filament at the center of the flow field within the nozzle. Step 3: Use an imaging spectrometer and a first ICCD camera to collect short-lived emission signals of carbon and nitrogen free radicals for pressure measurement, and use a second ICCD camera to collect long-lived emission signals of carbon and nitrogen free radicals for velocity measurement. Step 4: The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, and calculates and outputs the measured flow field velocity and pressure.

[0013] As described in the second aspect of the present invention, step 2 includes: after being irradiated by a femtosecond filament of an ultraviolet laser, a mixed gas of nitrogen and methane undergoes a photochemical reaction to generate excited carbon and nitrogen free radicals, which produce fluorescence. The concentration of methane in the mixed gas of nitrogen and methane is in the range of 500 ppm to 4000 ppm.

[0014] As described in the second aspect of the present invention, step 3 includes: setting the shutter speed of the first ICCD camera to 1 μs and setting the shutter speed of the second ICCD camera to 10 μs-50 μs.

[0015] As described in the second aspect of the present invention, step 4 of the measurement method includes the following sub-steps: Step 4.1: Spatial location of velocity signals collected at different times; obtain the displacement Δx of the carbon-nitrogen radical-labeled flow field region within time Δt; calculate the flow field velocity v according to the formula: v = Δx / Δt Where Δt is the time interval between the two signal acquisitions, and Δx is the displacement between the two signal acquisitions; Step 4.2: Perform spectral analysis on the pressure signal to obtain carbon and nitrogen free radicals B. 2 Σ+ -X 2 Σ + The spectral peak position λ of the (0,0) transition is used to determine the flow field pressure by combining the pre-calibrated peak position and pressure calibration curve.

[0016] The present invention has the following beneficial effects: 1. This invention analyzes the luminescence characteristics of carbon-nitrogen (CN) radicals, enabling simultaneous measurement of flow velocity and pressure. It achieves multi-parameter synchronous measurement without the need for additional measurement equipment, thus simplifying the system structure.

[0017] 2. Femtosecond lasers are used to induce the generation of carbon and nitrogen (CN) radicals from the components of the flow field itself (methane and nitrogen), eliminating the need for adding particles or probes. The non-invasive measurement method avoids interference with the flow field. At the same time, the femtosecond filament has one-dimensional spatial resolution, enabling simultaneous one-dimensional measurement of flow field velocity and pressure parameters, and has high spatial resolution.

[0018] 3. Methane concentration does not affect carbon and nitrogen (CN) radicals B. 2 Σ + -X 2 Σ + The spectral peak position shift of the (0,0) transition is applicable to flow fields with concentration fluctuations caused by turbulent mixing, and the measurement work has strong anti-interference ability.

[0019] 4. Simple optical system: Only one 267 nm femtosecond laser beam is required, eliminating the need for precise spatiotemporal overlap of multiple laser beams, which reduces system complexity and cost, and provides higher stability in high-noise environments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a device for simultaneously measuring flow velocity and pressure based on femtosecond laser molecular labeling proposed in this invention; Figure 2 This is a pressure calibration curve used in this invention to calculate pressure values ​​from spectral peaks.

[0021] Among them, 1-Titanium sapphire femtosecond laser; 2-Third harmonic module; 3-Spherical lens; 4-Nozzle; 5-Imaging spectrometer; 6-First ICCD camera; 7-Second ICCD camera; 8-Light receiver; 9-Computer. Detailed Implementation

[0022] The purpose of this invention is to provide a method and apparatus for simultaneous measurement of flow field velocity and pressure based on femtosecond laser molecular labeling. The optical system of this invention is simple. It uses a femtosecond laser to generate and label carbon-nitrogen (CN) radicals. The flow field pressure is measured by analyzing the spectral peak position shift of the short-lived emission of carbon-nitrogen (CN) radicals and the calibration relationship with pressure. The velocity is measured by combining the displacement of the long-lived emission of carbon-nitrogen (CN) radicals. This achieves non-invasive, high spatial resolution simultaneous measurement of flow field velocity and pressure.

[0023] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] Example 1 Appendix Figure 1 This is a schematic diagram of a device for simultaneously measuring flow velocity and pressure based on femtosecond laser molecular labeling, as proposed in this invention.

[0025] The first aspect of the present invention provides a device for simultaneously measuring flow velocity and pressure based on femtosecond laser molecular labeling, the measuring device comprising a femtosecond laser module, a flow field module, an optical focusing module, a signal acquisition module, and a data processing module; The femtosecond laser module is used to generate femtosecond lasers in the ultraviolet band; The optical focusing module focuses the femtosecond laser into a femtosecond filament and keeps the focal point of the femtosecond filament at the center of the flow field to be measured. The flow field module includes a nozzle made of a material transparent to femtosecond lasers. The mixed gas to be measured is introduced into the nozzle to generate the flow field to be measured for the mixed gas. The signal acquisition module includes: a speed signal acquisition device and a pressure signal acquisition device; The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, performs calculations, and outputs the calculated flow field velocity and pressure measurement results.

[0026] The data processing module can use a computer, which receives short-lifetime emission signals of carbon and nitrogen free radicals from a first ICCD camera and long-lifetime emission signals of carbon and nitrogen free radicals from a second ICCD camera. The computer calculates the flow field velocity and pressure measurement results at the same moment based on the two emission signals.

[0027] The measuring device as described in the first aspect of the present invention, wherein the femtosecond laser module comprises: a femtosecond laser, a laser frequency doubling unit, and a laser attenuator disposed after the laser frequency doubling unit, wherein the femtosecond laser generates an ultrashort pulse laser with a femtosecond pulse width, the laser frequency doubling unit is disposed on the transmission path of the femtosecond ultrashort pulse laser, and the aperture of the laser frequency doubling unit is greater than or equal to the diameter of the incident femtosecond ultrashort pulse laser beam; The laser frequency doubling unit performs frequency doubling on the femtosecond-level ultrashort pulse laser and outputs a frequency-doubled ultraviolet-band femtosecond-level ultrashort pulse laser. The ultraviolet-band femtosecond-level ultrashort pulse laser passes through a laser attenuator, and the output laser intensity can be adjusted by the laser attenuator.

[0028] This invention discloses a device for simultaneously measuring flow velocity and pressure based on femtosecond laser molecular labeling. The femtosecond laser module includes a Ti:sapphire femtosecond laser and a third-harmonic generation module. The Ti:sapphire laser is a tunable near-infrared laser that can be pumped by a xenon lamp or a semiconductor laser. This invention uses the Ti:sapphire femtosecond laser to output a femtosecond pulse laser with a center wavelength of 800 nm. This femtosecond pulse laser is then subjected to third-harmonic wavelength upconversion through the third-harmonic generation module to obtain an ultraviolet femtosecond laser with a center wavelength of 267 nm. The 267 nm ultraviolet femtosecond laser is used to excite the generation and luminescence of carbon and nitrogen (CN) free radicals in the flow field. The flow field module is a transparent nozzle into which a mixture of nitrogen and trace methane at a concentration of 500 ppm-4000 ppm is introduced to generate a flow field of methane and nitrogen mixture. A typical flow field module uses a nozzle to introduce a mixture of nitrogen and methane at a concentration of 1000 ppm to generate a flow field of methane and nitrogen mixture.

[0029] The femtosecond laser module generates a 267 nm femtosecond laser, which is focused into the flow field to be measured by the optical focusing module, generating pressure and velocity signals. The signal acquisition module simultaneously acquires the pressure and velocity signals and sends them to the data processing module for pressure and velocity calculation, thereby obtaining the flow field pressure and velocity measurement results.

[0030] The light beam passing through the transparent nozzle is absorbed by the light receiver to avoid measurement errors caused by reflected light.

[0031] The measuring device as described in the first aspect of the present invention, wherein the femtosecond laser is a Ti:sapphire femtosecond laser, and the Ti:sapphire femtosecond laser outputs a femtosecond laser with a center wavelength of 800 nm; The laser frequency doubling unit is a solid-state third frequency multiplier, which up-converts a femtosecond laser with a center wavelength of 800 nm into a femtosecond pulse laser with a center wavelength of 267 nm in the ultraviolet band.

[0032] The measuring apparatus as described in the first aspect of the present invention, wherein the mixed gas to be measured is generated by mixing nitrogen and methane of a predetermined concentration.

[0033] As described in the first aspect of the present invention, the pressure signal acquisition device includes an imaging spectrometer and a first ICCD camera; the imaging spectrometer and the first ICCD camera are used to receive the short-lifetime emission signals of carbon and nitrogen free radicals after the mixed gas is irradiated by a laser. The light incident slit of the imaging spectrometer is arranged in a direction parallel to the propagation direction of the femtosecond filament; The first ICCD camera is coupled to the imaging spectrometer to capture and collect the short-lifetime emission signals of carbon and nitrogen free radicals that are incident on the light incident slit of the imaging spectrometer after the mixed gas is irradiated by laser. The velocity signal acquisition device includes a second ICCD camera, the optical axis of which is set perpendicular to the flow direction of the mixed gas and the propagation direction of the femtosecond pulse laser, for capturing long-lifetime emission signals of carbon and nitrogen free radicals.

[0034] As described in the first aspect of the present invention, the optical focusing module includes a spherical lens or a concave mirror, wherein the focal point of the spherical lens or the concave mirror is located at the center of the flow field to be measured. When a spherical lens is used to focus a femtosecond laser, the two mirror surfaces of the spherical lens are coated with an antireflective coating whose center wavelength is located at the center wavelength of the ultraviolet laser, and the transmittance of the antireflective coating is ≥95%. When a concave mirror is used to focus a femtosecond laser, an anti-reflective coating is deposited on the reflective surface with a center wavelength located at the center wavelength of the ultraviolet laser, and the reflectivity of the anti-reflective coating is ≥99%.

[0035] Example 2 A second aspect of the present invention provides a measurement method for the simultaneous measurement device for flow field velocity and pressure based on femtosecond laser molecular labeling as described in any one of the preceding claims, the measurement method comprising the following steps: Step 1: Add a predetermined proportion of methane gas to the nitrogen gas to be measured in the injection flow field module, and inject the mixture of nitrogen gas and methane gas into the nozzle. The typical operation is as follows: add a trace amount of methane at a concentration of 1000 ppm to the nitrogen gas flow field to be measured. The methane serves as a carbon source for carbon-nitrogen (CN) radicals and does not affect the position of the spectral peaks of the emission of carbon-nitrogen (CN) radicals. Step 2: The nozzle is irradiated with a femtosecond pulsed laser of a specified center wavelength and pulse width, forming a femtosecond filament at the center of the flow field within the nozzle. Typically, a Ti:sapphire femtosecond laser with a center wavelength of 800 nm is used. A solid-state third harmonic frequency multiplier converts the 800 nm femtosecond laser into a 267 nm ultraviolet femtosecond pulsed laser. After being focused by a spherical lens with a focal length of 500 mm, a femtosecond filament is formed in the flow field. The femtosecond filament induces a photochemical reaction between methane and nitrogen, generating excited carbon-nitrogen (CN) radicals. These CN radicals then undergo a B2O reaction. 2 Σ + -X 2 Σ + The (0,0) transition produces light; Step 3: Short-lived emission signals of carbon and nitrile radicals are acquired using an imaging spectrometer and a first ICCD camera for pressure measurement. Simultaneously, long-lived emission signals of carbon and nitrile radicals are acquired using a second ICCD camera for velocity measurement. The first ICCD camera is set to a shutter speed of 1 μs for pressure measurement, while the second ICCD camera is set to a shutter speed of 10 μs–50 μs for velocity measurement. Step 4: The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, and calculates and outputs the measured flow field velocity and pressure.

[0036] Step 4.1: Spatial positioning of velocity signals collected at different times to obtain the displacement Δx of the carbon-nitrogen (CN) radical-labeled flow field region within time Δt, and calculation of the flow field velocity v according to the formula. v=Δx / Δt Where Δt is the time interval between the two collected velocity signals, and Δx is the displacement of the signal.

[0037] Step 4.2: Perform spectral analysis on the pressure signal to extract carbon-nitrogen (CN) radicals B. 2 Σ + -X 2 Σ + The spectral peak position λ of the (0,0) transition is used to determine the flow field pressure by combining the pre-calibrated spectral peak position λ with the pressure calibration curve.

[0038] The method for determining the flow field pressure by combining the pre-calibrated spectral peak position λ and the pressure calibration curve is as follows: Step 4.21: Perform measurements at standard gas pressure to obtain the correspondence between pressure and spectral peak λ, and plot the results as shown in the attached diagram. Figure 2 The pressure calibration curve shown is attached. Figure 2 In the diagram, the horizontal axis represents the pressure value, and the vertical axis represents the spectral peak position λ. Step 4.22: The data processing module performs spectral analysis on the pressure signal, calculates and outputs the measured carbon and nitrogen (CN) free radicals B. 2 Σ + -X 2 Σ + The spectral peak position λ of the (0,0) transition is determined; then, the pressure calibration curve generated in step 4.21 is queried, and the flow field pressure is determined by combining the pre-calibrated spectral peak position λ and the pressure calibration curve. The flow field pressure is determined by the spectral peak position λ.

[0039] When performing actual measurements, the position λ of the spectral peak is obtained from the measurement. Using λ and the calibration curve, the actual pressure value of the measurement can be obtained from the graph.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and are not intended to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the embodiments of the present invention should not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for simultaneously measuring flow field velocity and pressure based on femtosecond laser molecular labeling, characterized in that, The measuring device includes a femtosecond laser module, a flow field module, an optical focusing module, a signal acquisition module, and a data processing module; The femtosecond laser module is used to generate femtosecond lasers in the ultraviolet band; The optical focusing module focuses the femtosecond laser into a femtosecond filament and keeps the focal point of the femtosecond filament at the center of the flow field to be measured. The flow field module includes a nozzle made of a material transparent to femtosecond lasers. The mixed gas to be measured is introduced into the nozzle to generate the flow field to be measured for the mixed gas. The signal acquisition module includes: a speed signal acquisition device and a pressure signal acquisition device; The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, performs calculations, and outputs the calculated flow field velocity and pressure measurement results.

2. The measuring device as described in claim 1, characterized in that, The femtosecond laser module includes: a femtosecond laser, a laser frequency doubling unit, and a laser attenuator disposed after the laser frequency doubling unit. The femtosecond laser generates an ultrashort pulse laser with a femtosecond pulse width. The laser frequency doubling unit is disposed on the transmission path of the femtosecond ultrashort pulse laser, and the aperture of the laser frequency doubling unit is greater than or equal to the diameter of the incident femtosecond ultrashort pulse laser beam. The laser frequency doubling unit performs frequency doubling on the femtosecond-level ultrashort pulse laser and outputs a frequency-doubled ultraviolet-band femtosecond-level ultrashort pulse laser. The ultraviolet-band femtosecond-level ultrashort pulse laser passes through a laser attenuator, and the output laser intensity can be adjusted by the laser attenuator.

3. The measuring device as described in claim 2, characterized in that, The femtosecond laser is a Ti:sapphire femtosecond laser, which outputs a femtosecond laser with a center wavelength of 800 nm. The laser frequency doubling unit is a solid-state third frequency multiplier, which up-converts a femtosecond laser with a center wavelength of 800 nm into a femtosecond pulse laser with a center wavelength of 267 nm in the ultraviolet band.

4. The measuring device as described in claim 1, characterized in that, The gas mixture to be measured is generated by mixing nitrogen and methane of a predetermined concentration.

5. The measuring device as described in claim 1, characterized in that, The pressure signal acquisition device includes an imaging spectrometer and a first ICCD camera; the imaging spectrometer and the first ICCD camera are used to receive the short-lifetime emission signals of carbon and nitrogen free radicals after the mixed gas is irradiated by laser. The light incident slit of the imaging spectrometer is arranged in a direction parallel to the propagation direction of the femtosecond filament; The first ICCD camera is coupled to the imaging spectrometer to capture and collect the short-lifetime emission signals of carbon and nitrogen free radicals that are incident on the light incident slit of the imaging spectrometer after the mixed gas is irradiated by laser. The velocity signal acquisition device includes a second ICCD camera, the optical axis of which is set perpendicular to the flow direction of the mixed gas and the propagation direction of the femtosecond pulse laser, for capturing long-lifetime emission signals of carbon and nitrogen free radicals.

6. The measuring device as described in claim 1, characterized in that, The optical focusing module includes a spherical lens or a concave mirror, wherein the focal point of the spherical lens or the concave mirror is located at the center of the flow field to be measured. When a spherical lens is used to focus a femtosecond laser, the two mirror surfaces of the spherical lens are coated with an antireflective coating whose center wavelength is located at the center wavelength of the ultraviolet laser, and the transmittance of the antireflective coating is ≥95%. When a concave mirror is used to focus a femtosecond laser, an anti-reflective coating is deposited on the reflective surface with a center wavelength located at the center wavelength of the ultraviolet laser, and the reflectivity of the anti-reflective coating is ≥99%.

7. A measurement method for a flow field velocity and pressure simultaneously measured by a femtosecond laser molecular labeling device as described in any one of claims 1-6, characterized in that, The measurement method includes the following steps: Step 1: Add a predetermined proportion of methane gas to the nitrogen gas to be measured in the injection flow field module, and inject the mixture of nitrogen gas and methane gas into the nozzle. Step 2: Focus a femtosecond pulsed laser with a specified center wavelength and pulse width onto the nozzle to form a femtosecond filament at the center of the flow field within the nozzle. Step 3: Use an imaging spectrometer and a first ICCD camera to collect short-lived emission signals of carbon and nitrogen free radicals for pressure measurement, and use a second ICCD camera to collect long-lived emission signals of carbon and nitrogen free radicals for velocity measurement. Step 4: The data processing module receives the sensor signals from the velocity signal acquisition device and the pressure signal acquisition device, and calculates and outputs the measured flow field velocity and pressure.

8. The measurement method as described in claim 7, characterized in that, Step 2 includes: after being irradiated by the femtosecond filament of the ultraviolet laser, the mixed gas of nitrogen and methane undergoes a photochemical reaction to generate excited carbon and nitrogen free radicals, which produce fluorescence. The concentration of methane in the mixed gas of nitrogen and methane is in the range of 500 ppm to 4000 ppm.

9. The measurement method as described in claim 7, characterized in that, Step 3 includes: setting the shutter speed of the first ICCD camera to 1μs and setting the shutter speed of the second ICCD camera to 10μs-50μs.

10. The measurement method as described in claim 8, characterized in that, Step 4 includes the following sub-steps: Step 4.1: Spatial location of velocity signals collected at different times; obtain the displacement Δx of the carbon-nitrogen radical-labeled flow field region within time Δt; calculate the flow field velocity v according to the formula: v = Δx / Δt Where Δt is the time interval between the two signal acquisitions, and Δx is the displacement between the two signal acquisitions; Step 4.2: Perform spectral analysis on the pressure signal to obtain carbon and nitrogen free radicals B. 2 Σ + -X 2 Σ + The spectral peak position λ of the (0,0) transition is used to determine the flow field pressure by combining the pre-calibrated peak position and pressure calibration curve.

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