In-situ velocimetry system and method based on Doppler frequency shift laser-induced breakdown spectroscopy

Abstract

This invention proposes an in-situ velocimetry system and method based on Doppler frequency shift laser-induced breakdown spectroscopy, comprising a working chamber body and a single-pulse all-solid-state laser, a photodetector, an oscilloscope, a LIBS front-end optical path, a LIBS spectrometer, an ICCD camera, a DG535 timing controller, and an electronic control module. The single-pulse all-solid-state laser, LIBS spectrometer, and ICCD camera are all electrically connected to the DG535 timing controller, and the photodetector is electrically connected to the oscilloscope. The LIBS front-end optical path includes a laser beam splitter, a dichroic mirror, a concave lens, a double-lens combination, a broadband beam splitter prism, a fiber-optic coupling lens, a broadband reflector, a convex lens, a microscope objective, and a neutral density filter. This invention combines laser-induced breakdown spectroscopy technology with the Doppler frequency shift effect, and uses image-based methods to provide flow velocity support for LIBS detection, integrating all equipment and components into a single instrument to build a complete and sophisticated LIBS flow velocity detection system.

Description

Technical Field

[0001] This invention belongs to the field of aerospace science and technology and combustion flow field diagnostic measurement technology, specifically relating to a laser-induced breakdown spectroscopy in-situ velocimetry system and method based on Doppler frequency shift. Background Technology

[0002] With the continuous development of national aerospace technology, higher demands are being placed on the advancement of aircraft propulsion technology. Research on hypersonic flight propulsion systems has become a key area of ​​technological competition among nations and is an important national strategic resource. The combustion plume of a rocket engine consists of the combustion and pyrolysis products of the propellant discharged through the nozzle after ignition. Its velocity is a crucial parameter revealing engine performance. Monitoring the flow velocity effectively allows for the inversion of fuel combustion conditions and analysis of engine operating status, providing an important basis for engine performance evaluation, optimization design, and propellant improvement.

[0003] Currently, flame velocity measurement in combustion fields can be divided into two types: contact and non-contact measurement. Contact measurements mainly include methods such as velocimeters and hot-wire anemometers, but these methods have drawbacks such as slow response time, low spatial resolution, and interference with the plume field. Non-contact measurements include optical methods and acoustic methods. In comparison, measurement techniques based on optical methods have attracted much attention, such as particle image velocimetry (PIV), laser Doppler velocimetry (LDV), tunable semiconductor laser absorption spectroscopy (TDLAS), and planar laser-induced fluorescence (PLIF) technology.

[0004] In the actual detection of high-dynamic combustion fields, PLIF technology has a fast response speed and high spatial resolution, but it requires the addition of tracer particles. Due to the uncontrollability of solid propellant combustion, it is difficult to make the tracer particles uniformly distributed in the flow field, and the particle signal is easily annihilated by the strong flame radiation signal. TDLAS spectroscopy technology has high spectral resolution, but it requires the combustion plume to pass through its optical reflection cavity, making on-site operation complex and the response time long. PIV technology can perform full-field measurements, but it requires the addition of tracer particles and has a low sampling frequency. Therefore, the above measurement methods all have certain limitations in practical applications. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a laser-induced breakdown spectroscopy in-situ velocimetry system and method based on Doppler frequency shift. This system combines laser-induced breakdown spectroscopy technology with the optical Doppler effect, and innovatively proposes a dynamic combustion field wide-range flow velocity in-situ measurement method based on the Doppler frequency shift of the LIBS spectral peak. It focuses on breakthroughs in remote, variable-focus LIBS signal enhancement detection technology and effective signal extraction under high temperature, high pressure, high turbidity and strong interference environments in combustion fields.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an in-situ velocimetry system for laser-induced breakdown spectroscopy based on Doppler frequency shift, characterized in that it includes a working chamber body and a single-pulse all-solid-state laser, a photodetector, an oscilloscope, a LIBS front-end optical path, a LIBS spectrometer, an ICCD camera, a DG535 timing controller, and an electronic control module disposed within the working chamber body; the single-pulse all-solid-state laser, the LIBS spectrometer, and the ICCD camera are all electrically connected to the DG535 timing controller, and the photodetector is electrically connected to the oscilloscope;

[0007] The LIBS front optical path includes a laser beam splitter, a dichroic mirror, a concave lens, a dual-lens combination, a broadband beam splitter prism, a fiber optic coupling lens, a broadband reflector, a convex lens, a microscope objective, and a neutral density filter.

[0008] The pulsed laser emitted by the single-pulse all-solid-state laser is sequentially passed through a laser beam splitter and a dichroic mirror, and then focused into the combustion flame by a concave lens and a combination of two lenses to generate a LIBS signal. The LIBS signal is then reflected back through the combination of two lenses and the concave lens, becoming parallel plasma radiation light. After being reflected by the dichroic mirror, the plasma radiation light is split into a transmitted light beam and a reflected light beam by a broadband beam splitter. The reflected light is coupled to the optical fiber by an optical fiber coupling lens and transmitted to the LIBS spectrometer to complete the detection of the LIBS signal spectral information of the combustion field. At the same time, the transmitted light is sequentially passed through a broadband reflector and a convex lens, focused to one focal length of the convex lens, and then converted into a plasma image signal by a microscope objective and magnified by a factor of 1. The intensity of the plasma image signal is then attenuated by a neutral density filter, and finally the plasma image information of the LIBS signal of the combustion field is acquired by an ICCD camera.

[0009] The photodetector is used to receive the pulsed laser reflected by the laser beam splitter, and then transmits the pulsed laser signal to an oscilloscope to display the laser pulse width.

[0010] Preferably, the concave lens is mounted on a linear motor, which is electrically connected to an electronic control module. The electronic control module controls the movement of the linear motor, thereby controlling the spacing between the concave lens and the double lens combination, and changing the actual focusing distance of the laser.

[0011] Preferably, the electronic control module includes a control module, a power supply module, and a communication module, which are electrically connected to each other. The control module controls the linear motor, and the power supply module is electrically connected to and supplies power to the single-pulse all-solid-state laser, photodetector, oscilloscope, LIBS spectrometer, ICCD camera, DG535 timing controller, and electronic control module. The communication module is used for communication between the LIBS spectrometer, ICCD camera, and control module via USB.

[0012] Preferably, the dual-lens assembly consists of a crescent-shaped lens and a convex lens, with the crescent-shaped lens positioned closer to the concave lens.

[0013] Preferably, the laser beam splitter is an Nd:YAG laser beam splitter with a transmission-to-reflection ratio of 9:1; the cutoff wavelength of the dichroic mirror is 900nm; and the transmission-to-reflection ratio of the broadband beam splitter is 5:5.

[0014] In addition, the present invention also provides an in-situ velocimetry method based on Doppler frequency shift laser-induced breakdown spectroscopy. This velocimetry method relies on the aforementioned velocimetry system and includes:

[0015] The single-pulse all-solid-state laser is turned on and continuously emits laser pulses. The laser pulses are focused onto the combustion field flame through the LIBS front optical path. The LIBS spectrometer is triggered by the DG535 timing controller. After a certain time interval t1 after the laser pulse emission, the LIBS spectrometer is turned on to start acquiring the LIBS signal spectral information of the combustion field. The acquisition time of the spectral signal is t2, and the LIBS signal spectral signal of the combustion field is obtained. The ICCD camera is triggered by the DG535 timing controller. After a certain time interval t3 after the laser pulse emission, the ICCD camera is turned on to start acquiring plasma image information. The acquisition time of the plasma image information is t4.

[0016] Preferably, the acquisition of LIBS signal spectral information and plasma image information of the combustion field is divided into two modes: one is a time-resolved acquisition mode, in which the distance between the concave lens and the double lens combination is not changed to achieve fixed-point detection of the combustion field, thereby obtaining the time change process of plasma radiation information of the combustion field; the other is a spatial resolution acquisition mode, in which the distance between the concave lens and the double lens combination is adjusted to obtain the longitudinal spatial plasma radiation information of the combustion field, which is used to analyze the spatial velocity change process of the combustion field at different spatial locations.

[0017] Preferably, the value range of t1 is 0 to 100 μs; the value range of t2 is 0.1 to 5 μs; the value range of t3 is 0 to 1 μs; and the value range of t4 is 0 to 1 μs.

[0018] This invention combines an optical system with a single-pulse all-solid-state laser, a LIBS spectrometer, and an ICCD camera to provide a novel integrated detection system for combustion field flow velocity detection and a new method for in-situ measurement of combustion field flow velocity using this system.

[0019] This invention combines laser-induced breakdown spectroscopy with the optical Doppler effect, using an optical path system to simultaneously acquire plasma spectral information and images. Through spectral preprocessing and peak identification algorithms, and by analyzing the changes in plasma image information with flow velocity, it develops a method for accurate flame velocity inversion based on image-assisted laser-induced breakdown spectral Doppler frequency shift.

[0020] This invention achieves remote spatial resolution measurement of combustion field flow velocity by adjusting the spacing between a concave lens and a double-lens combination to change the actual focusing distance of the laser. The invention mounts the concave lens on a linear motor, and an electronic control module controls the linear motor to automatically adjust the spacing, thus completing the spatial resolution measurement of combustion field flow velocity.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention combines laser-induced breakdown spectroscopy with the Doppler frequency shift effect, and uses image-based methods to provide flow velocity support for LIBS detection. All equipment and devices are integrated into a single instrument, establishing a complete and sophisticated LIBS flow velocity detection system. By optimizing the optical path, the use of devices is minimized, and the size of the instrument is significantly reduced, providing a new approach and technological breakthrough for LIBS flow velocity measurement in combustion fields.

[0023] 2. This invention designs a remote zoom flow velocity detection optical path based on the same optical path system to simultaneously acquire LIBS spectral information and image information. After the emitted 1064nm laser pulse excites the flame in the combustion field, the generated plasma signal is divided into transmitted light and reflected light by a broadband beam splitter, which are collected by the LIBS spectrometer and the ICCD camera respectively, thus completing the simultaneous detection of the flow velocity spectral information and image of the combustion field.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the detection device disclosed in Embodiment 1 of the present invention.

[0026] Figure 2 This is a schematic diagram of the LIBS front optical path structure disclosed in Embodiment 1 of the present invention.

[0027] Among them, 1—single-pulse all-solid-state laser; 2—photodetector; 3—oscilloscope; 5—LIBS spectrometer; 6—ICCD camera; 7—DG535 timing controller; 8—laser beam splitter; 9—dichroic mirror; 10—concave lens; 11—linear motor; 12—double lens combination; 13—broadband beam splitter prism; 14—fiber optic coupling lens; 15—broadband reflector; 16—convex lens; 17—microscope objective; 18—neutral density filter; 19—electronic control module; 20—work chamber body. Detailed Implementation

[0028] Example 1

[0029] like Figure 1 and 2 As shown in the figure, this embodiment presents an in-situ velocimetry system based on Doppler frequency shift laser-induced breakdown spectroscopy (LIBS). This system effectively combines LIBS technology and the optical Doppler effect, and includes: a working chamber body 20 and a single-pulse all-solid-state laser 1, a photodetector 2, an oscilloscope 3, a LIBS front-end optical path, a LIBS spectrometer 5, an ICCD camera 6, a DG535 timing controller 7, and an electronic control module 19 disposed within the working chamber body 20; the single-pulse all-solid-state laser 1, the LIBS spectrometer 5, and the ICCD camera 6 are all electrically connected to the DG535 timing controller 7, and the photodetector 2 is electrically connected to the oscilloscope 3;

[0030] A single-pulse all-solid-state laser 1 serves as the excitation source, which is focused into the combustion flame through a LIBS pre-focusing optical path. The LIBS pre-focusing optical path includes a laser beam splitter 8, a dichroic mirror 9, a concave lens 10, a dual-lens assembly 12, a broadband beam splitter prism 13, a fiber-coupled lens 14, a broadband reflector 15, a convex lens 16, a microscope objective 17, and a neutral density filter 18. The optical elements in the LIBS pre-focusing optical path are arranged within the working chamber body 20 according to the following working process: The pulsed laser emitted by the single-pulse all-solid-state laser 1 passes sequentially through the laser beam splitter 8 and the dichroic mirror 9, and is then focused into the combustion flame through the concave lens 10 and the dual-lens assembly 12 to generate a LIBS signal. The LIBS signal is then reflected back through the dual-lens assembly 12 and the concave lens 10. The plasma radiation light then becomes parallel, is reflected by the dichroic mirror 9, and is divided into a transmitted beam and a reflected beam by the broadband beam splitter prism 13. The reflected beam is coupled to the optical fiber by the fiber-coupled lens 14 and transmitted to the LIBS spectrometer 5 to complete the detection of the LIBS signal spectral information of the combustion field. At the same time, the transmitted light passes through the broadband mirror 15 and the convex lens 16 in sequence, is focused to one focal length of the convex lens 16, and then is converted into a plasma image signal by the microscope objective 17 and magnified by a factor of 1. The intensity of the plasma image signal is then attenuated by the neutral density filter 18, and finally the plasma image information of the LIBS signal of the combustion field is acquired by the ICCD camera 6.

[0031] The photodetector 2 is used to receive the pulsed laser reflected by the laser beam splitter 8, and then transmit the pulsed laser signal to the oscilloscope 3 to display the laser pulse width.

[0032] In this embodiment, the concave lens 10 is mounted on the linear motor 11, which is electrically connected to the electronic control module 19. The electronic control module 19 controls the movement mode of the linear motor 11, thereby controlling the distance between the concave lens 10 and the double lens combination 12 and changing the actual focusing distance of the laser.

[0033] In this embodiment, the fundamental wavelength of the single-pulse all-solid-state laser 1 is 1064 nm, the generated nanosecond laser pulse width is less than 10 ns, and the maximum pulse energy exceeds 200 mJ. The LIBS spectrometer 5 has a spectral range of 200-880 nm and a spectral resolution of 0.3 nm. The ICCD camera 6 includes a spectral acquisition mode and an image acquisition mode.

[0034] In this embodiment, the electronic control module 19 includes a control module, a power supply module, and a communication module, which are electrically connected to each other. The control module is used to control the linear motor 11. The power supply module is electrically connected to and supplies power to the single-pulse all-solid-state laser 1, photodetector 2, oscilloscope 3, LIBS spectrometer 5, ICCD camera 6, DG535 timing controller 7, and electronic control module 19. The communication module is used for communication between the LIBS spectrometer 5, ICCD camera 6, and control module via USB.

[0035] In this embodiment, the dual-lens assembly 12 consists of a crescent-shaped lens and a convex lens. The crescent-shaped lens is positioned closer to the concave lens 10. This structure can significantly reduce spherical aberration to improve laser focusing quality.

[0036] The diameter of the dual-lens assembly 12 is 4 inches, and the diameters of the concave lens 10, fiber-coupled lens 14, and convex lens 16 are all 1 inch. The magnification of the microscope objective 17 is 40x.

[0037] In this embodiment, the laser beam splitter 8 is an Nd:YAG laser beam splitter with a transmission-to-reflection ratio of 9:1; the cutoff wavelength of the dichroic mirror 9 is 900nm; and the transmission-to-reflection ratio of the broadband beam splitter 13 is 5:5.

[0038] In this embodiment, the photodetector 2 is a photodiode.

[0039] Example 2

[0040] This embodiment presents an in-situ velocimetry method based on Doppler frequency shift laser-induced breakdown spectroscopy. This velocimetry method relies on the velocimetry system described in Embodiment 1 and includes:

[0041] First, the operating parameters of the single-pulse all-solid-state laser 1 and the LIBS spectrometer 5 are set.

[0042] The single-pulse all-solid-state laser 1 is selected in internal trigger mode. It is turned on and continuously emits laser pulses, which are focused onto the combustion flame through the LIBS front optical path. The LIBS spectrometer 5 is in external trigger mode, triggered by the DG535 timing controller 7. Because the plasma induced by the pulsed laser initially exhibits strong continuous background radiation, a certain time delay is required to avoid interference from this radiation and obtain discrete characteristic spectral signals. Therefore, after a certain time interval t1 following laser pulse emission, the LIBS spectrometer 5 is turned on to begin acquiring the LIBS signal spectral information of the combustion field. The acquisition duration is t2, obtaining the LIBS signal spectral signal of the combustion field. The ICCD camera 6 is in external trigger mode, triggered by the DG535 timing controller 7. After a certain time interval t3 following laser pulse emission, the ICCD camera 6 is turned on to begin acquiring plasma image information. The acquisition duration is t4.

[0043] The pulsed laser emitted by the single-pulse all-solid-state laser 1 is sequentially passed through a laser beam splitter 8 and a dichroic mirror 9, and then focused into the combustion field flame by a concave lens 10 and a double lens combination 12 to generate a LIBS signal. The LIBS signal is reflected back through the double lens combination 12 and the concave lens 10 and becomes parallel plasma radiation light. After being reflected by the dichroic mirror 9, the plasma radiation light is divided into a transmitted light beam and a reflected light beam by a broadband beam splitter prism 13. The reflected light is coupled to the optical fiber by an optical fiber coupling lens 14 and transmitted to the LIBS spectrometer 5 to complete the detection of the LIBS signal spectral information of the combustion field. At the same time, the transmitted light is sequentially passed through a broadband reflector 15 and a convex lens 16, and focused to a focal length of the convex lens 16. Then, the transmitted light is converted into a plasma image signal by a microscope objective 17 and magnified by a factor of 1. The intensity of the plasma image signal is then attenuated by a neutral density filter 18. Finally, the plasma image information of the LIBS signal of the combustion field is acquired by an ICCD camera 6.

[0044] The photodetector 2 is used to receive the pulsed laser reflected by the laser beam splitter 8, and then transmit the pulsed laser signal to the oscilloscope 3 to display the laser pulse width.

[0045] In this embodiment, the concave lens 10 is mounted on the linear motor 11, which is electrically connected to the electronic control module 19. The electronic control module 19 controls the movement mode of the linear motor 11, thereby controlling the distance between the concave lens 10 and the double lens combination 12 and changing the actual focusing distance of the laser.

[0046] In this embodiment, the acquisition of LIBS signal spectral information and plasma image information of the combustion field is divided into two modes. One is the time-resolved acquisition mode. In the time-resolved acquisition mode, the distance between the concave lens 10 and the dual lens combination 12 is not changed to realize the fixed-point detection of the combustion field, thereby obtaining the time change process of the plasma radiation information of the combustion field. The other is the spatial resolution acquisition mode. In the spatial resolution acquisition mode, the distance between the concave lens 10 and the dual lens combination 12 is adjusted to obtain the longitudinal spatial plasma radiation information of the combustion field, which is used to analyze the spatial velocity change process of the combustion field at different spatial locations.

[0047] In this embodiment, the value of t1 ranges from 0 to 100 μs, and t1 is preferably set to 0.5 μs during the experiment; the value of t2 ranges from 0.1 to 5 μs, and since plasma radiation typically lasts for tens of microseconds, t2 is preferably set to 1 ms during the experiment; the value of t3 ranges from 0 to 1 μs, and t3 is preferably set to 0.1 μs during the experiment; the value of t4 ranges from 0 to 1 μs, and t4 is preferably set to 50 μs during the experiment.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A laser-induced breakdown spectroscopy in-situ velocimetry system based on Doppler frequency shift, characterized in that, The system includes a working chamber body (20) and a single-pulse all-solid-state laser (1), a photodetector (2), an oscilloscope (3), a LIBS front optical path, a LIBS spectrometer (5), an ICCD camera (6), a DG535 timing controller (7), and an electronic control module (19) installed in the working chamber body (20); the single-pulse all-solid-state laser (1), the LIBS spectrometer (5), and the ICCD camera (6) are all electrically connected to the DG535 timing controller (7), and the photodetector (2) is electrically connected to the oscilloscope (3); The LIBS front optical path includes a laser beam splitter (8), a dichroic mirror (9), a concave lens (10), a double lens combination (12), a broadband beam splitter prism (13), a fiber optic coupling lens (14), a broadband reflector (15), a convex lens (16), a microscope objective (17), and a neutral density filter (18). The pulsed laser emitted by the single-pulse all-solid-state laser (1) is sequentially passed through a laser beam splitter (8) and a dichroic mirror (9), and then focused into the combustion flame by a concave lens (10) and a double-lens combination (12) to generate a LIBS signal. The LIBS signal is then reflected back through the double-lens combination (12) and the concave lens (10) and becomes parallel plasma radiation light. After being reflected by the dichroic mirror (9), the plasma radiation light is divided into a transmitted light beam and a reflected light beam by a broadband beam splitter prism (13). The reflected light beam is then coupled by an optical fiber-coupled lens (14) to separate the plasma radiation spectrum. The signal is coupled to an optical fiber and transmitted to a LIBS spectrometer (5) to complete the detection of LIBS signal spectral information of the combustion field; at the same time, the transmitted light passes through a broadband mirror (15) and a convex lens (16) in sequence, and is focused to a focal length of one convex lens (16). Then, the transmitted light is converted into a plasma image signal by a microscope objective (17) and magnified by a factor of several. The intensity of the plasma image signal is then attenuated by a neutral density filter (18). Finally, the plasma image information of the LIBS signal of the combustion field is acquired by an ICCD camera (6). The photodetector (2) is used to receive the pulsed laser reflected by the laser beam splitter (8), and then transmits the pulsed laser signal to the oscilloscope (3) to display the laser pulse width; The concave lens (10) is mounted on the linear motor (11), which is electrically connected to the electronic control module (19). The electronic control module (19) controls the movement mode of the linear motor (11), thereby controlling the distance between the concave lens (10) and the double lens combination (12) and changing the actual focusing distance of the laser. The electronic control module (19) includes a control module, a power supply module, and a communication module, which are electrically connected to each other. The control module is used to control the linear motor (11). The power supply module is electrically connected to and supplies power to the single-pulse all-solid-state laser (1), photodetector (2), oscilloscope (3), LIBS spectrometer (5), ICCD camera (6), DG535 timing controller (7), and electronic control module (19). The communication module is used for communication between the LIBS spectrometer (5), ICCD camera (6), and control module via USB. The dual-lens assembly (12) consists of a crescent-shaped lens and a convex lens, with the crescent-shaped lens positioned near the concave lens (10).

2. The laser-induced breakdown spectroscopy in-situ velocimetry system based on Doppler frequency shift according to claim 1, characterized in that, The laser beam splitter (8) is an Nd:YAG laser beam splitter with a transmission-to-reflection ratio of 9:1; the cutoff wavelength of the dichroic mirror (9) is 900 nm; and the transmission-to-reflection ratio of the broadband beam splitter (13) is 5:

5.

3. A laser-induced breakdown spectroscopy in-situ velocimetry method based on Doppler frequency shift, wherein the velocimetry method relies on the velocimetry system described in claim 1 or 2, characterized in that, The speed measurement method includes: The single-pulse all-solid-state laser (1) is turned on and continuously emits laser pulses. The laser pulses are focused into the combustion field flame through the LIBS front optical path. The LIBS spectrometer (5) is triggered by the DG535 timing controller (7). After a certain time t1 after the laser pulse is emitted, the LIBS spectrometer (5) is turned on and begins to collect the LIBS signal spectrum information of the combustion field. The duration of the spectrum signal collection is t2, and the LIBS signal spectrum signal of the combustion field is obtained. The ICCD camera (6) is triggered by the DG535 timing controller (7). After a certain time t3 after the laser pulse is emitted, the ICCD camera (6) is turned on and begins to collect plasma image information. The duration of the plasma image information collection is t4.

4. The in-situ velocimetry method based on Doppler frequency shift laser-induced breakdown spectroscopy according to claim 3, characterized in that, The acquisition of LIBS signal spectral information and plasma image information of the combustion field is divided into two modes. One is the time-resolved acquisition mode. In the time-resolved acquisition mode, the distance between the concave lens (10) and the double lens combination (12) is not changed to realize the fixed-point detection of the combustion field, thereby obtaining the time change process of the plasma radiation information of the combustion field. The other is the spatial resolution acquisition mode. In the spatial resolution acquisition mode, the distance between the concave lens (10) and the double lens combination (12) is adjusted to obtain the longitudinal spatial plasma radiation information of the combustion field, which is used to analyze the spatial velocity change process of the combustion field at different spatial locations.

5. The in-situ velocimetry method based on Doppler frequency shift laser-induced breakdown spectroscopy according to claim 3, characterized in that, The value of t1 ranges from 0 to 100 μs; the value of t2 ranges from 0.1 to 5 μs; the value of t3 ranges from 0 to 1 μs; and the value of t4 ranges from 0 to 1 μs.

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