A method and device for plasma diagnosis based on femtosecond laser filament probe

Abstract

The application relates to a kind of plasma diagnostic method and device based on femtosecond laser filament probe, belong to laser plasma diagnostic technical field, method utilizes the high peak power characteristics of femtosecond laser to form the femtosecond filament probe with only hundred microns in diameter and only several millimeters in length, and the internal substance of plasma can be excited again.Spectra signals when using and not using femtosecond filament probe are collected respectively, and the element information at the position of femtosecond filament probe at this moment is obtained by differentiating the spectrum.By scanning the relative position of femtosecond filament probe and plasma, the material content information at different spatial positions in plasma can be obtained, and by changing the delay time when femtosecond laser pulse and plasma are generated, the material distribution information in plasma at different time can be obtained, and the four-dimensional distribution information of the material in plasma can be obtained by coincidence of the spectrum under different positions and different delay times.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser plasma diagnosis, and in particular relates to a plasma diagnosis method and device based on a femtosecond laser filamentation probe. Background Art

[0002] Plasma is the fourth state of matter. Several methods are commonly used to generate plasma in the laboratory, one of which is to focus a high-energy pulsed laser onto the surface of a sample to produce laser plasma. Laser plasmas exhibit characteristics such as transient behavior, uneven temporal and spatial distribution, high temperature, high density, and high pressure. Laser plasmas have a wide range of applications in inertial confinement fusion, extreme ultraviolet (EUV) light sources and lithography, pulsed laser deposition, and plasma spectroscopy. Achieving multi-dimensional, high-temporal and spatial resolution imaging of matter in laser plasmas is crucial for laser plasma control and its applications.

[0003] For example, in the field of inertial confinement fusion, precise measurement of plasma properties and fusion reaction products is crucial for a comprehensive understanding of the laser absorption mechanism and the optimal coupling conditions between the laser driver and the target material. The compression and heating of a small amount of fusion fuel in inertial confinement fusion usually occur on an extremely small spatial scale, which places strict requirements on the temporal and spatial resolution of laser plasma diagnostic technology. For extreme ultraviolet lithography, the spatiotemporal distribution and expansion dynamics of laser-induced tin plasma play a decisive role in optimizing the extreme ultraviolet light conversion efficiency. By precisely controlling the laser plasma, the negative thermal effects and particle problems in micromachining can be alleviated, thereby improving the processing quality and efficiency. Therefore, multi-dimensional diagnosis of substances in plasma plays an irreplaceable role in understanding the physical mechanism of processing and providing a theoretical basis and technical support for process optimization.

[0004] At present, conventional plasma diagnosis and imaging methods are mainly faced with the following difficulties: (1) time-space integration effect. Taking laser plasma as an example, laser plasma has the characteristics of high temperature and high density, and the physical and chemical properties of laser plasma have a large gradient of change in different time-space distributions. Conventional plasma diagnosis and imaging methods, such as plasma spectroscopy and imaging methods, can only regard the plasma as a whole and can only obtain the characteristic information of the plasma projected on a certain plane. For example, rapid photography technology can only observe the outline of the plasma in a two-dimensional plane and cannot obtain the evolution process of more dimensions. Moreover, this projection measurement method makes the gradient change information in the plasma obscured by the spatial path integration effect. At the same time, in laser absorption spectroscopy technology, the element distribution and content at a certain position in the plasma can be obtained by measuring the light intensity of the continuous laser passing through the plasma. However, due to the use of a continuous laser light source, the measurement results will also be affected by the time integration effect. Therefore, the time-space integration effect faced by conventional plasma diagnostic methods makes it difficult to obtain multi-dimensional local information in the plasma. (2) The imaging resolution is low. The size of the plasma is usually in the millimeter range, while the diffusion length of the particles in the plasma is usually in the micrometer range. In addition, the ionization and relaxation time of the particles in the plasma are often in the nanosecond range. In order to obtain higher spatial and temporal resolution, higher requirements are placed on the detection technology. (3) The existing detection methods cannot achieve multi-dimensional and multi-substance diagnosis. The use of non-optical detection technology (such as Langmuir probe, microwave method, etc.) can only obtain information such as the temperature and electron density of the plasma, and cannot analyze the material composition and its distribution in the plasma. The use of optical detection technology such as laser absorption spectroscopy and laser-induced fluorescence spectroscopy (LIF) can only achieve the detection of a single material component in the plasma, and cannot achieve multi-substance diagnosis and multi-dimensional imaging.

[0005] Therefore, in order to address the problems faced in plasma diagnosis, such as the influence of the space-time integration effect, low space-time resolution, and the inability to achieve material analysis in three-dimensional space and time dimensions, while also avoiding interference with the plasma state during the diagnosis process, it is necessary to propose a plasma diagnostic method and device. Summary of the Invention

[0006] To address the above-mentioned problems in the prior art, the present invention provides a plasma diagnostic method and device based on a femtosecond laser filamentation probe. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0007] The present invention provides a plasma diagnostic method based on a femtosecond laser filamentation probe, comprising:

[0008] focusing a femtosecond laser to form a femtosecond filamentation probe, exciting plasma through the femtosecond filamentation probe, and obtaining a femtosecond laser-induced breakdown spectroscopy signal;

[0009] Tuning the three-dimensional spatial position of the femtosecond filamentation probe in the plasma to obtain femtosecond laser-induced breakdown spectroscopy signals at different spatial positions, and collecting diagnostic and imaging signals of substances in the plasma at different spatial positions;

[0010] Adjusting the delay interval for forming the plasma and the femtosecond filamentation probe, and synchronously adjusting the delay interval of the femtosecond laser induced breakdown spectroscopy signal, respectively obtaining femtosecond laser induced breakdown spectroscopy signals with different delay intervals, and collecting diagnostic and imaging signals of substances in the plasma at different delay intervals;

[0011] Without using the femtosecond filamentation probe, collecting plasma spectrum signals of substances in the plasma not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval;

[0012] Differential processing is performed on the diagnostic and imaging signals of the substance in the plasma at different spatial positions, the diagnostic and imaging signals of the substance in the plasma at different delay intervals, and the plasma spectrum signals of the substance in the plasma not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval to obtain the femtosecond laser filamentation probe excitation spectrum signals of the substance in the plasma at different spatial positions and at different delay intervals.

[0013] In one embodiment of the present invention, the plasma is laser-induced plasma, which is obtained by focusing a pulsed laser to ablate the surface of a target material to be measured.

[0014] In one embodiment of the present invention, focusing a femtosecond laser to form a femtosecond filamentation probe, and exciting plasma through the femtosecond filamentation probe comprises:

[0015] The femtosecond laser is emitted by a femtosecond laser, and after reflection and focusing, a femtosecond filamentation probe is formed;

[0016] The femtosecond filamentation probe passes through the plasma, and local species of the plasma are re-excited at the center of the femtosecond filamentation probe.

[0017] In one embodiment of the present invention, the diameter of the femtosecond filamentation probe is hundreds of microns.

[0018] In one embodiment of the present invention, tuning the three-dimensional spatial position of the femtosecond filamentation probe in the plasma comprises:

[0019] tuning the position of the femtosecond filamentation probe along a first direction in the plasma by a first plane mirror;

[0020] tuning the position of the femtosecond filamentation probe along a second direction in the plasma by a second plane mirror;

[0021] tuning the position of the femtosecond filamentation probe along a third direction in the plasma through a first converging lens;

[0022] The first direction, the second direction and the third direction are perpendicular to each other.

[0023] The present invention also provides a plasma diagnostic device based on a femtosecond laser filamentation probe, which is used to implement the above-mentioned plasma diagnostic method based on a femtosecond laser filamentation probe. The device includes: a plasma generating system, which is used to generate laser-induced plasma by focusing a pulsed laser to ablate the surface of a target material to be measured;

[0024] A femtosecond filamentation probe detection system is used to focus a femtosecond laser to form a femtosecond filamentation probe, and to excite a plasma through the femtosecond filamentation probe to obtain a femtosecond laser-induced breakdown spectroscopy signal; the femtosecond filamentation probe detection system is disposed on a first three-dimensional translation stage to tune the three-dimensional spatial position of the femtosecond filamentation probe in the plasma;

[0025] a digital delay generator for adjusting the delay interval for forming the plasma and the femtosecond filamentation probe, and synchronously adjusting the delay interval of the femtosecond laser-induced breakdown spectroscopy signal;

[0026] a spectral signal acquisition system for acquiring diagnostic and imaging signals of substances in the plasma at different spatial positions and diagnostic and imaging signals of substances in the plasma at different delay intervals, and further for acquiring plasma spectral signals of substances in the plasma not excited by the femtosecond filamentation probe at the same spatial position and at the same delay interval; the spectral signal acquisition system is disposed on a second three-dimensional translation stage to tune the three-dimensional spatial position of the spectral signal acquisition system;

[0027] The spectral signal acquisition system is communicatively connected to an external data processing platform, and the external data processing platform is used to process and obtain femtosecond laser filamentation probe excitation spectral signals of substances in the plasma at different spatial positions and at different delay intervals.

[0028] In one embodiment of the present invention, the plasma generation system includes: an ablation laser, a third plane reflector, a second converging lens and a rotating stage, wherein the target material to be measured is set on the rotating stage, and the ablation laser is used to emit pulsed laser, which passes through the third plane reflector and the second converging lens in sequence along the optical path and is focused on the surface of the target material to be measured to excite and obtain laser-induced plasma.

[0029] In one embodiment of the present invention, the femtosecond filamentation probe detection system includes: a femtosecond laser, a first plane mirror, a second plane mirror and a first converging lens, wherein the femtosecond laser is used to emit femtosecond laser, and the femtosecond laser passes through the first plane mirror, the second plane mirror and the first converging lens in sequence along the optical path to form a femtosecond filamentation probe, and the femtosecond filamentation probe passes through the laser-induced plasma and re-excites the local matter of the laser-induced plasma.

[0030] In one embodiment of the present invention, the spectral signal acquisition system includes: a collection lens group, a fiber optic probe and a spectrometer, wherein the collection lens group is used to collect femtosecond laser-induced breakdown spectroscopy signals and is coupled to the fiber optic probe; the fiber optic probe is connected to the spectrometer, and the spectrometer is used to collect the femtosecond laser-induced breakdown spectroscopy signals to obtain diagnostic and imaging signals of the plasma.

[0031] In one embodiment of the present invention, the digital delay generator is used to adjust the delay intervals between the ablation laser, the femtosecond laser and the spectrometer respectively.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The plasma diagnostic method based on a femtosecond laser filamentation probe of the present invention utilizes the high peak power of a femtosecond laser to form a femtosecond filamentation probe with a diameter of only a few hundred microns and a length of only a few millimeters, which can re-excite materials within the plasma. Spectral signals are then collected when the femtosecond filamentation probe is in use and when it is not, and the spectra are differentiated to obtain elemental information at the position of the femtosecond filamentation probe at that moment. By scanning the relative position of the femtosecond filamentation probe and the plasma, information on the material content at different spatial locations within the plasma is obtained. By varying the delay time between the femtosecond laser pulse and the moment of plasma generation, information on the material distribution within the plasma at different times can be obtained. The spectra at different locations and with different delay times are then processed to obtain four-dimensional distribution information of the materials within the plasma, effectively overcoming the difficulties faced by existing plasma diagnostic technologies.

[0034] The plasma diagnostic device, based on a femtosecond laser filamentation probe, collects femtosecond laser-induced breakdown spectroscopy signals to diagnose and image localized materials in the plasma. A three-dimensional translation stage controls the femtosecond filamentation probe's movement through different locations in the plasma, while a digital delay generator controls the delay interval, enabling diagnosis and imaging of the plasma in both three spatial and temporal dimensions.

[0035] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following preferred embodiments are specifically cited and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a flow chart of a plasma diagnostic method based on a femtosecond laser filamentation probe provided by an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of the principle of a plasma diagnostic method based on a femtosecond laser filamentation probe provided by an embodiment of the present invention;

[0038] Figure 3 3D scanning principle diagram of a plasma diagnostic method based on a femtosecond laser filamentation probe provided by an embodiment of the present invention;

[0039] Figure 4 It is a schematic diagram of a diagnostic example of a plasma diagnostic device based on a femtosecond laser filamentation probe provided in an embodiment of the present invention.

[0040] Figure numerals: 1-ablation laser; 2-third plane mirror; 3-second converging lens; 4-rotating stage; 5-femtosecond laser; 6-first plane mirror; 7-second plane mirror; 8-first converging lens; 9-collection lens group; 10-fiber probe; 11-spectrometer; 12-digital delay generator; 13-optical trash can; 100-target material to be measured; 200-laser-induced plasma; 300-external data processing platform. DETAILED DESCRIPTION

[0041] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a plasma diagnostic method and device based on a femtosecond laser filamentation probe proposed in accordance with the present invention, in conjunction with the accompanying drawings and specific implementation methods.

[0042] The aforementioned and other technical contents, features, and effects of the present invention are clearly presented in the following detailed description of the specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a deeper and more specific understanding of the technical means and effects adopted by the present invention to achieve the intended purpose can be obtained. However, the accompanying drawings are provided for reference and illustration purposes only and are not intended to limit the technical solutions of the present invention.

[0043] Example 1

[0044] Existing plasma diagnostic technologies include optical and non-optical ones. Optical diagnostic technologies include laser-induced breakdown spectroscopy, laser absorption spectroscopy, laser-induced fluorescence spectroscopy, rapid photography, and laser Thomson scattering. Taking laser-induced fluorescence spectroscopy as an example, its advantage lies in its non-contact diagnosis. However, it can only detect a single component in the plasma and is limited by the time-space integration effect, resulting in the measurement results covering all information over a period of time or space. Therefore, the measurement results are usually two-dimensional projections and cannot reflect the four-dimensional information of the plasma. In addition, due to the use of micro-nanosecond light sources, its temporal resolution is poor and it cannot form micro-filamentation channels, which also limits its spatial resolution. Non-optical diagnostic technologies, such as Langmuir probes, can achieve three-dimensional diagnosis of plasmas. However, diagnostic methods based on these probes require intrusion into the plasma, which will interfere with the plasma state and cannot image and diagnose substances in the plasma.

[0045] In view of this, this embodiment provides a plasma diagnostic method based on a femtosecond laser filamentation probe, such as Figures 1 to 3 As shown, Figure 1 This is a flow chart of a plasma diagnostic method based on a femtosecond laser filamentation probe provided by an embodiment of the present invention; Figure 2 Schematic diagram of the principle of a plasma diagnostic method based on a femtosecond laser filamentation probe provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the three-dimensional scanning principle of the plasma diagnostic method based on the femtosecond laser filamentation probe provided by an embodiment of the present invention.

[0046] In this embodiment, the plasma diagnostic method based on the femtosecond laser filamentation probe includes:

[0047] Step 1: Focus the femtosecond laser to form a femtosecond filamentation probe, excite the plasma through the femtosecond filamentation probe, and obtain the femtosecond laser-induced breakdown spectroscopy signal.

[0048] In an optional embodiment, step 1 specifically includes:

[0049] Step 1.1: Focusing a femtosecond laser to form a femtosecond filamentation probe, and exciting plasma through the femtosecond filamentation probe, including:

[0050] Step 1.2: The femtosecond laser is emitted from the femtosecond laser, which is reflected and focused to form a femtosecond filamentation probe;

[0051] Step 1.3: The femtosecond filamentation probe is passed through the plasma, and the local material in the plasma is re-excited at the center of the femtosecond filamentation probe to obtain a femtosecond laser-induced breakdown spectroscopy signal.

[0052] For example, the diameter of the femtosecond filamentation probe is only a few hundred microns, and the length is only a few millimeters. The interaction time between the femtosecond filamentation probe and the plasma is only on the order of femtoseconds. For example, the diameter of the femtosecond filamentation probe is 100 microns, the length ranges from 5 to 10 millimeters, and the interaction time between the femtosecond filamentation probe and the plasma is 100 femtoseconds, which gives the diagnostic results the advantage of high temporal and spatial resolution.

[0053] Step 2: Tune the three-dimensional spatial position of the femtosecond filamentation probe in the plasma to obtain femtosecond laser-induced breakdown spectroscopy signals at different spatial positions, and collect diagnostic and imaging signals of substances in the plasma at different spatial positions.

[0054] In an optional embodiment, in step 2, tuning the three-dimensional spatial position of the femtosecond filamentation probe in the plasma includes:

[0055] tuning the position of the femtosecond filamentation probe along a first direction in the plasma by a first plane mirror;

[0056] tuning the position of the femtosecond filamentation probe along the second direction in the plasma by a second plane mirror;

[0057] tuning the position of the femtosecond filamentation probe along the third direction in the plasma through a first converging lens;

[0058] The first direction, the second direction and the third direction are perpendicular to each other.

[0059] Step 3: Adjusting the delay intervals for forming the plasma and the femtosecond filamentation probe, and synchronously adjusting the delay intervals for the femtosecond laser-induced breakdown spectroscopy signal, respectively, to obtain femtosecond laser-induced breakdown spectroscopy signals with different delay intervals, and collecting diagnostic and imaging signals of substances in the plasma at different delay intervals;

[0060] Step 4: without using the femtosecond filamentation probe, collecting plasma spectrum signals of substances in the plasma that are not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval;

[0061] Step 5: Perform differential processing on the diagnostic and imaging signals of the substances in the plasma at different spatial positions, the diagnostic and imaging signals of the substances in the plasma at different delay intervals, and the plasma spectrum signals of the substances in the plasma not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval, to obtain the femtosecond laser filamentation probe excitation spectrum signals of the substances in the plasma at different spatial positions and at different delay intervals.

[0062] It is understandable that the plasma of this embodiment can be generated by laser induction, or by excitation such as an electric arc or microwave. The following description will only take laser-induced plasma as an example, but the present invention is not limited to this. Exemplarily, the plasma is a laser-induced plasma, which is obtained by focusing a pulsed laser to ablate the surface of the target material to be measured. In addition, the pulsed laser can be incident perpendicular to the surface of the target material to be measured or form a certain angle of incidence with the surface of the target material to be measured, which is not limited in this embodiment. Similarly, the femtosecond filamentation probe can be parallel to the surface of the target material to be measured and perpendicular to the pulsed laser, or it can also pass through the plasma at a certain angle.

[0063] Exemplarily, the principle of differential processing is to subtract the spectrum that has not been re-excited by the femtosecond filamentation probe under the same spatial and temporal conditions from the spectrum excited by the femtosecond filamentation probe, that is, to collect the plasma spectrum signal at the same spatial position and the same delay interval as the spectrum after re-excitation, but not re-excited by the femtosecond filamentation probe, and then obtain the femtosecond laser filamentation probe excitation spectrum signal of the substance in the plasma at different spatial positions and at different delay intervals through differential processing.

[0064] Notably, the femtosecond filamentation probe of the present invention enables measurement of localized species within a plasma without being affected by spatiotemporal path effects. Furthermore, because the measured spectral signal is that of the re-excited plasma, it contains spectral line information for multiple elements, enabling simultaneous diagnosis and imaging of multiple elements in the plasma.

[0065] The plasma diagnostic method based on a femtosecond laser filamentation probe of the present invention utilizes the high peak power of a femtosecond laser to form a femtosecond filamentation probe with a diameter of only a few hundred microns and a length of only a few millimeters, which can re-excite materials within the plasma. Spectral signals are then collected when the femtosecond filamentation probe is in use and when it is not, and the spectra are differentiated to obtain elemental information at the position of the femtosecond filamentation probe at that moment. By scanning the relative position of the femtosecond filamentation probe and the plasma, information on the material content at different spatial locations within the plasma is obtained. By varying the delay time between the femtosecond laser pulse and the moment of plasma generation, information on the material distribution within the plasma at different times can be obtained. The spectra at different locations and with different delay times are then processed to obtain four-dimensional distribution information of the materials within the plasma, effectively overcoming the difficulties faced by existing plasma diagnostic technologies.

[0066] It can be understood that the purpose of the present invention is to diagnose plasma based on a femtosecond laser filamentation probe. Through coincidence processing, that is, after simultaneously collecting position information and time information, the four-dimensional distribution of plasma can be obtained by superposition of position information and time information. However, the coincidence processing of the spectrum is not the content of this application, so it is not described in detail. Related content can also refer to relevant existing technologies.

[0067] Example 2

[0068] To address the problems faced by existing plasma diagnostic technologies, such as the time-space integration effect, low time-space resolution, and the inability to perform material analysis in three-dimensional space and time dimensions, and to avoid interference with the plasma state, this embodiment uses femtosecond laser filamentation as a probe for plasma diagnosis.

[0069] This embodiment provides a plasma diagnostic device based on a femtosecond laser filamentation probe, such as Figures 2 to 4 As shown, Figure 4 It is a schematic diagram of a diagnostic example of a plasma diagnostic device based on a femtosecond laser filamentation probe provided in an embodiment of the present invention.

[0070] In this embodiment, a plasma diagnostic device based on a femtosecond laser filamentation probe is used to implement the plasma diagnostic method based on a femtosecond laser filamentation probe in Example 1. The device includes: a plasma generation system, a femtosecond filamentation probe detection system, a digital delay generator 12 and a spectral signal acquisition system.

[0071] Specifically, the plasma generation system is used to obtain laser-induced plasma 200 by focusing pulsed laser to ablate the surface of the target material 100 to be measured; the femtosecond filamentation probe detection system is used to focus the femtosecond laser to form a femtosecond filamentation probe, and excite the plasma through the femtosecond filamentation probe to obtain a femtosecond laser-induced breakdown spectrum signal; the femtosecond filamentation probe detection system is arranged on a first three-dimensional translation stage to tune the three-dimensional spatial position of the femtosecond filamentation probe in the plasma; the digital delay generator 12 is used to adjust the delay interval between the formation of the plasma and the femtosecond filamentation probe, and synchronously adjust the delay interval of the femtosecond laser-induced breakdown spectrum signal; the spectral signal acquisition system is used to collect diagnostic and imaging signals of substances in the plasma at different spatial positions and diagnostic and imaging signals of substances in the plasma at different delay intervals, and is also used to collect plasma spectral signals of substances in the plasma that are not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval; the spectral signal acquisition system is arranged on a second three-dimensional translation stage to tune the three-dimensional spatial position of the spectral signal acquisition system.

[0072] In an optional embodiment, the plasma generation system includes: an ablation laser 1, a third plane reflector 2, a second converging lens 3 and a rotating table 4, wherein the target material 100 to be measured is set on the rotating table 4, and the ablation laser 1 is used to emit pulsed laser, which passes through the third plane reflector 2 and the second converging lens 3 in sequence along the optical path and is focused on the surface of the target material 100 to be measured to excite and obtain laser-induced plasma 200.

[0073] For example, the ablation laser 1 can be a nanosecond laser light source, and a picosecond or femtosecond laser light source can also be used as an alternative. It is only necessary to ensure that the ablation laser power density reaches the ablation threshold of the target material 100 to be measured. For example, the filamentation power density can be set to 1GW / cm 2 It is understandable that, due to the different ablation characteristics of the target material 100 to be measured, the ablation threshold is not limited in this embodiment, and the relevant threshold can be realized by referring to the relevant existing technology, so it is not described in detail.

[0074] In an optional embodiment, a femtosecond filamentation probe detection system includes: a femtosecond laser 5, a first plane mirror 6, a second plane mirror 7, and a first converging lens 8. The femtosecond laser 5 is used to emit a femtosecond laser, which passes through the first plane mirror 6, the second plane mirror 7, and the first converging lens 8 in sequence along an optical path to form a femtosecond filamentation probe. The femtosecond filamentation probe passes through the laser-induced plasma 200 and re-excites localized matter in the laser-induced plasma 200 at the center of the femtosecond filamentation probe. Exemplarily, an optical trash can 13 is disposed on the rear optical path of the laser-induced plasma 200. After the femtosecond filamentation probe re-excites the laser-induced plasma 200, the remaining laser light that passes through the laser-induced plasma 200 is collected by the optical trash can 13.

[0075] Preferably, the femtosecond laser 5 may be a titanium sapphire femtosecond laser, and may also be a fiber femtosecond laser, an all-solid-state femtosecond laser, or a similar femtosecond laser light source.

[0076] In an optional embodiment, the spectral signal acquisition system includes: a collection lens group 9, a fiber optic probe 10 and a spectrometer 11, wherein the collection lens group 9 is used to collect femtosecond laser-induced breakdown spectroscopy signals and couple them into the fiber optic probe 10; the fiber optic probe 10 is connected to the spectrometer 11, and the spectrometer 11 is used to collect femtosecond laser-induced breakdown spectroscopy signals to obtain diagnostic and imaging signals of the plasma.

[0077] Preferably, the spectrometer 11 is a spectral signal acquisition device, which can use a grating spectrometer, a fiber spectrometer or a mid-step spectrometer, etc., or a photodiode or photomultiplier tube detector equipped with a narrowband filter to achieve high-sensitivity detection.

[0078] It is noteworthy that the plasma diagnostic device based on the femtosecond laser filamentation probe of this embodiment uses the femtosecond filamentation probe to perform local secondary excitation within the plasma and utilizes the collection lens group 9 for micro-imaging acquisition. The collected femtosecond laser-induced breakdown spectrum signal contains characteristic spectral lines of multiple substances, which can achieve simultaneous diagnosis and imaging of multiple substances in the plasma, making up for the deficiency of existing technologies in achieving high temporal and spatial resolution material imaging. At the same time, as a non-contact non-destructive testing method, the femtosecond filamentation probe can obtain local material spectral information through non-contact non-destructive testing. The measurement results are not limited by the temporal and spatial integration effect and can reflect the local material information in the plasma. In addition, because the femtosecond filamentation probe has a spatial scale of only hundreds of microns and can achieve a spatial resolution of hundreds of microns by mapping the core diameter of the optical fiber probe 10 onto the laser-induced plasma 200, the interaction time between the femtosecond filamentation probe and the laser-induced plasma 200 is only on the order of femtoseconds, which has a higher temporal resolution than the plasma duration.

[0079] In an optional embodiment, the digital delay generator 12 is used to adjust the delay intervals between the ablation laser 1 , the femtosecond laser 5 and the spectrometer 11 respectively.

[0080] In an optional embodiment, the spectral signal acquisition system is communicatively connected to an external data processing platform 300, and the external data processing platform 300 is used to process and obtain femtosecond laser filamentation probe excitation spectral signals of substances in the plasma at different spatial positions and at different delay intervals.

[0081] It should be noted that the diagnostic device provided in the second embodiment of the present invention has similar beneficial effects as the diagnostic method in the first embodiment. Therefore, for the technical details not disclosed therein, reference can be made to the description of the first embodiment for understanding.

[0082] The working principle of the plasma diagnostic device based on the femtosecond laser filamentation probe of this embodiment is as follows:

[0083] The ablation laser 1 emits a pulsed laser, which is focused onto the surface of the target material 100 to be measured through the third plane reflector 2 and the second converging lens 3 in sequence. When the laser power density on the surface of the target material 100 to be measured exceeds its threshold, a laser-induced plasma 200 is generated. At the same time, the rotating stage 4 can be used to change the ablation position of the laser on the surface of the target material 100 to be measured.

[0084] The femtosecond laser 5 emits a beam of high-intensity ultrashort pulsed laser light, which is converged by the first converging lens 8 to form a femtosecond filamentation probe. The femtosecond filamentation probe passes through the laser-induced plasma 200, re-exciting the substances in the laser-induced plasma 200 to obtain a femtosecond laser-induced breakdown spectroscopy signal. The remaining laser light is collected by the optical trash can 13. The femtosecond laser-induced breakdown spectroscopy signal is collected by the collection lens group 9 through 1:1 imaging and coupled into the optical fiber probe 10. The core diameter of the optical fiber probe 10 is mapped onto the plasma to ensure that the spatial resolution of the spectral probe is at the level of hundreds of microns. The optical fiber probe 10 is connected to the spectrometer 11, and the femtosecond laser-induced breakdown spectroscopy signal is further collected by the spectrometer 11. At the same time, the spectrometer 11 is connected to the external data processing platform 300 for communication. After processing by the external data processing platform 300, the diagnostic and imaging results can be obtained.

[0085] For ease of understanding, the y direction represents the first direction, the x direction represents the second direction, and the z direction represents the third direction, wherein the y direction, the x direction, and the z direction are perpendicular to each other.

[0086] Furthermore, a high-intensity, ultrashort pulse laser beam is emitted from a femtosecond laser 5 and reflected sequentially by a first plane mirror 6 and a second plane mirror 7. The pitch angle of the first plane mirror 6 is adjusted to change the position of the femtosecond filamentation probe in the laser-induced plasma 200 along the y-direction. The second plane mirror 7 is mounted on a translation stage, which can be adjusted to enable movement of the femtosecond filamentation probe in the x-direction. A first converging lens 8 is mounted on another translation stage, which can be adjusted to enable movement of the femtosecond filamentation probe in the z-direction. Simultaneously, a collection lens assembly 9 and a fiber optic probe 10 are mounted on a second three-dimensional translation stage. This second three-dimensional translation stage can be adjusted according to the different positions of the femtosecond filamentation probe in the plasma, thereby enabling synchronous acquisition of spectral signals and ultimately achieving three-dimensional scanning of the femtosecond filamentation probe in the plasma.

[0087] It can be understood that both the first three-dimensional translation stage and the second three-dimensional translation stage can adopt composite translation stages, and the first three-dimensional translation stage and the second three-dimensional translation stage can realize synchronous adjustment of the second plane reflector 7, the first converging lens 8, the collection lens group 9 and the optical fiber probe 10.

[0088] Furthermore, the triggering and delay time between the ablation laser 1, the femtosecond laser 5 and the spectrometer 11 are all controlled by a digital delay generator 12 and are interconnected through data lines. Therefore, on the basis of performing three-dimensional scanning in the plasma using a femtosecond filamentation probe, the acquisition time of the spectral signal is adjusted by the digital delay generator 12, thereby realizing four-dimensional imaging of the matter in the plasma.

[0089] The plasma diagnostic device based on a femtosecond laser filamentation probe of the present invention enables diagnosis and imaging of localized materials in the plasma by collecting femtosecond laser-induced breakdown spectroscopy signals. By controlling the femtosecond filamentation probe's movement through different locations in the plasma using a three-dimensional translation stage and controlling the delay interval using a digital delay generator 12, diagnosis and imaging of the plasma in both three spatial and temporal dimensions are achieved.

[0090] It should be noted that, in this document, relational terms such as first and second are used solely to distinguish one entity or operation from another, and do not necessarily require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "include," or any other variations thereof are intended to encompass non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not explicitly listed. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or device comprising the element. Terms such as "connected" or "connected" are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. References to orientations or positional relationships, such as "upper," "lower," "left," and "right," are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate description and simplify the description of the present invention. They do not indicate or imply that the device or element referred to must have, be constructed, or operate in a specific orientation, and are therefore not to be construed as limiting the present invention.

[0091] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A plasma diagnostic method based on a femtosecond laser filamentation probe, characterized in that: include: focusing a femtosecond laser to form a femtosecond filamentation probe, exciting plasma through the femtosecond filamentation probe, and obtaining a femtosecond laser-induced breakdown spectroscopy signal; Tuning the three-dimensional spatial position of the femtosecond filamentation probe in the plasma to obtain femtosecond laser-induced breakdown spectroscopy signals at different spatial positions, and collecting diagnostic and imaging signals of substances in the plasma at different spatial positions; Adjusting the delay interval for forming the plasma and the femtosecond filamentation probe, and synchronously adjusting the delay interval of the femtosecond laser induced breakdown spectroscopy signal, respectively obtaining femtosecond laser induced breakdown spectroscopy signals with different delay intervals, and collecting diagnostic and imaging signals of substances in the plasma at different delay intervals; Without using the femtosecond filamentation probe, collecting plasma spectrum signals of substances in the plasma not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval; Differential processing is performed on the diagnostic and imaging signals of the substance in the plasma at different spatial positions, the diagnostic and imaging signals of the substance in the plasma at different delay intervals, and the plasma spectrum signals of the substance in the plasma not excited by the femtosecond filamentation probe at the same spatial position and the same delay interval to obtain the femtosecond laser filamentation probe excitation spectrum signals of the substance in the plasma at different spatial positions and at different delay intervals.

2. The plasma diagnostic method based on femtosecond laser filamentation probe according to claim 1, characterized in that: The plasma is laser-induced plasma, which is obtained by focusing a pulsed laser to ablate the surface of a target material to be measured.

3. The plasma diagnostic method based on femtosecond laser filamentation probe according to claim 2, characterized in that: Focusing a femtosecond laser to form a femtosecond filamentation probe, and exciting plasma through the femtosecond filamentation probe, comprising: The femtosecond laser is emitted by a femtosecond laser, and after reflection and focusing, a femtosecond filamentation probe is formed; The femtosecond filamentation probe passes through the plasma, and local species of the plasma are re-excited at the center of the femtosecond filamentation probe.

4. The plasma diagnostic method based on femtosecond laser filamentation probe according to claim 1, characterized in that: The diameter of the femtosecond filamentation probe is hundreds of microns.

5. The plasma diagnostic method based on femtosecond laser filamentation probe according to claim 1, characterized in that: Tuning the three-dimensional spatial position of the femtosecond filamentation probe in the plasma comprises: tuning the position of the femtosecond filamentation probe along a first direction in the plasma by a first plane mirror; tuning the position of the femtosecond filamentation probe along a second direction in the plasma by a second plane mirror; tuning the position of the femtosecond filamentation probe along a third direction in the plasma through a first converging lens; The first direction, the second direction and the third direction are perpendicular to each other.

6. A plasma diagnostic device based on a femtosecond laser filamentation probe, characterized in that: A device for implementing the plasma diagnostic method based on a femtosecond laser filamentation probe according to any one of claims 1 to 5 comprises: A plasma generation system, used to generate laser-induced plasma by ablating the surface of a target material to be measured through pulsed laser focusing; A femtosecond filamentation probe detection system is used to focus a femtosecond laser to form a femtosecond filamentation probe, and to excite a plasma through the femtosecond filamentation probe to obtain a femtosecond laser-induced breakdown spectroscopy signal; the femtosecond filamentation probe detection system is disposed on a first three-dimensional translation stage to tune the three-dimensional spatial position of the femtosecond filamentation probe in the plasma; a digital delay generator for adjusting the delay interval for forming the plasma and the femtosecond filamentation probe, and synchronously adjusting the delay interval of the femtosecond laser-induced breakdown spectroscopy signal; a spectral signal acquisition system for acquiring diagnostic and imaging signals of substances in the plasma at different spatial positions and diagnostic and imaging signals of substances in the plasma at different delay intervals, and further for acquiring plasma spectral signals of substances in the plasma not excited by the femtosecond filamentation probe at the same spatial position and at the same delay interval; the spectral signal acquisition system is disposed on a second three-dimensional translation stage to tune the three-dimensional spatial position of the spectral signal acquisition system; The spectral signal acquisition system is communicatively connected to an external data processing platform, and the external data processing platform is used to process and obtain femtosecond laser filamentation probe excitation spectral signals of substances in the plasma at different spatial positions and at different delay intervals.

7. The plasma diagnostic device based on a femtosecond laser filamentation probe according to claim 6, characterized in that: The plasma generation system includes: an ablation laser, a third plane reflector, a second converging lens, and a rotating stage, wherein the target material to be measured is placed on the rotating stage, and the ablation laser is used to emit pulsed laser light. The pulsed laser light passes through the third plane reflector and the second converging lens in sequence along an optical path, and is focused onto the surface of the target material to be measured to excite and obtain laser-induced plasma.

8. The plasma diagnostic device based on a femtosecond laser filamentation probe according to claim 7, characterized in that: The femtosecond filamentation probe detection system includes: a femtosecond laser, a first plane mirror, a second plane mirror, and a first converging lens, wherein the femtosecond laser is used to emit femtosecond laser light, and the femtosecond laser passes through the first plane mirror, the second plane mirror, and the first converging lens in sequence along an optical path to form a femtosecond filamentation probe, and the femtosecond filamentation probe passes through the laser-induced plasma and re-excites local matter in the laser-induced plasma.

9. The plasma diagnostic device based on a femtosecond laser filamentation probe according to claim 8, characterized in that: The spectral signal acquisition system includes: a collection lens group, a fiber optic probe and a spectrometer, wherein the collection lens group is used to collect femtosecond laser-induced breakdown spectroscopy signals and is coupled to the fiber optic probe; the fiber optic probe is connected to the spectrometer, and the spectrometer is used to collect the femtosecond laser-induced breakdown spectroscopy signals to obtain plasma diagnostic and imaging signals.

10. The plasma diagnostic device based on a femtosecond laser filamentation probe according to claim 9, characterized in that: The digital delay generator is used to adjust the delay intervals between the ablation laser, the femtosecond laser and the spectrometer respectively.

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