A method and system for characterizing laser plasma flow field pressure

Abstract

The application relates to a method and system for characterizing laser plasma flow field pressure, comprising the following steps: irradiating the surface of discrete particle accumulation by a pulsed laser to generate laser plasma; adjusting the laser parameters to change the generated laser plasma flow field pressure, and capturing the particle jet formed by the laser plasma flow field acceleration; analyzing the captured particle jet to obtain the particle jet speed or kinetic energy parameters; obtaining the laser plasma flow field pressure according to the obtained particle jet speed or kinetic energy parameters under different laser parameters; and characterizing the laser plasma flow field pressure generated under different laser parameters by the particle jet speed. The application directly relates the particle jet speed to the laser plasma flow field pressure, and constructs a method for conveniently, quickly, timely and in-situ characterizing the laser plasma flow field pressure generated when laser ablation of discrete micro-particle accumulation by measuring the macroscopically visible particle jet.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of laser-induced breakdown spectroscopy and flow field detection, and particularly relates to a method for characterizing laser plasma flow field pressure. BACKGROUND

[0002] When laser-induced breakdown spectroscopy (LIBS) technology is used for in-situ remote sensing analysis of the chemical composition of the surface of field geological materials, for example, when the spectral camera MarSCoDe (the first LIBS planetary material composition analyzer in China) carried by the Chinese Mars rover Zhurong is performing the task of analyzing the chemical composition of the surface of soil and rock, a layer of sand dust often covers the surface of the object to be analyzed. In this case, before the LIBS system formally starts the surface composition analysis function, a new task must first be completed, that is, the sand dust covering (usually with a millimeter-level accumulation thickness and a micron-level particle size) on the surface of the object to be analyzed must be removed by laser.

[0003] The process of removing the sand dust covering by laser involves the interaction of laser and discrete particle accumulation, and the main working principle is as follows: a strong laser pulse irradiates the surface of the particles, causing the irradiated particles to melt and evaporate, forming a high-speed laser plasma flow; the laser plasma flow is supported by the surface of the particles and moves upward at a high speed perpendicular to the target surface; at the same time, the target surface receives the reaction force of the laser plasma flow and obtains a recoil momentum, so that part of the surface particles obtain a momentum downward perpendicular to the surface of the particles; the particles driven to move vertically downward start a digging process, and finally achieve the purpose of local particle removal. Therefore, the efficiency of laser sand dust removal depends on the pressure of the laser plasma flow field generated by the removal laser pulse. In order to evaluate and optimize the sand dust removal efficiency of the LIBS system in real time while performing the task in the field, there is an urgent need for a method for quickly, conveniently, and in-situ characterizing the pressure of the laser plasma flow field generated when laser ablation of particle accumulation.

[0004] Currently, the pressure of the laser plasma flow field generated when laser interacts with hard solid materials is usually characterized by measuring the impulse transferred to the target during laser ablation based on a torsion or pendulum device. However, these methods are not suitable for discrete particle accumulation. The main reason is that the particle accumulation is a soft material, which can dissipate the recoil momentum obtained from the laser ablation process, so that it cannot be presented in the form of a swing angle as hard solid materials do.

[0005] Therefore, the existing method for characterizing the pressure of the laser plasma flow field generated when laser interacts with hard solid materials by measuring the impulse transferred to the target during laser ablation based on a torsion or pendulum device is not suitable for discrete particle accumulation. SUMMARY

[0006] The present application provides a method for characterizing laser plasma flow field pressure based on laser-driven particle jet, which is suitable for convenient, fast, real-time and in-situ characterization of laser plasma flow field pressure.

[0007] To solve the above technical problems, the technical scheme of the present application is as follows:

[0008] A method for characterizing laser plasma flow field pressure, comprising the steps of:

[0009] S10. Irradiating the surface of a discrete particle accumulation with a pulsed laser to generate a laser plasma;

[0010] S20. Adjusting laser parameters to change the generated laser plasma flow field pressure, and capturing the particle jet formed by the laser plasma flow field acceleration;

[0011] S30. Analyzing the captured particle jet to obtain corresponding particle jet speed or kinetic energy parameters under different laser parameters;

[0012] S40. Obtaining the laser plasma flow field pressure according to the obtained corresponding particle jet speed or kinetic energy parameters under different laser parameters, to obtain the corresponding relationship between the laser plasma flow field pressure and the particle jet speed;

[0013] S50. Characterizing the laser plasma flow field pressure generated under different laser parameters by the particle jet speed.

[0014] Further, as a preferred technical scheme, in step S20, the capture of the particle jet is specifically:

[0015] The particle jet formed by the laser plasma flow field acceleration is captured by a high-speed camera.

[0016] Further, as a preferred technical scheme, in step S30, the kinetic energy parameters include:

[0017] The average impact force experienced by the particles captured by the high-speed camera in the particle jet in the flow field, the cross-sectional area of the impact force experienced by the particles captured by the high-speed camera in the particle jet, the average lifetime of the laser plasma flow field, the mass of the particles captured by the high-speed camera in the particle jet, and the speed of the particles captured by the high-speed camera in the particle jet.

[0018] Further, as a preferred technical scheme, step S40 specifically includes:

[0019] According to the pressure formula and the law of conservation of energy, in combination with the acquired particle jet speed or kinetic energy parameters corresponding to different laser parameters, the laser plasma flow field pressure is acquired, so as to obtain the corresponding relationship between the laser plasma flow field pressure and the particle jet speed.

[0020] Further, as a preferred technical solution,

[0021] The laser plasma flow field pressure is the effect of the unit area force on the particles in the laser plasma flow field, and the effect of the unit area force on the particles in the laser plasma flow field can be represented by the average flow field pressure.

[0022] The laser plasma flow field pressure is acquired by the following formula:

[0023]

[0024] Wherein: P is the average flow field pressure, F is the average impact force on the particles in the particle jet captured by the high-speed camera in the flow field, A is the cross-sectional area of the particles in the particle jet captured by the high-speed camera, t is the average lifetime of the laser plasma flow field, is the mass of the particles in the particle jet captured by the high-speed camera, and v is the speed of the particles in the particle jet captured by the high-speed camera.

[0025] Further, as a preferred technical solution, step S50 specifically comprises:

[0026] The particle jet speed is used as an observable probe to draw a particle jet speed curve with laser parameter changes, so as to characterize the laser plasma flow field pressure generated under different laser parameters.

[0027] Further, as a preferred technical solution, the laser parameters specifically include:

[0028] Laser wavelength, laser pulse energy or distance from focal plane to discrete particle accumulation surface.

[0029] Further, as a preferred technical solution, step S10 specifically comprises:

[0030] The discrete particle accumulation surface is irradiated by the focused pulse laser provided by the LIBS system to generate laser plasma.

[0031] Further, as a preferred technical solution, the acquisition of the particle jet speed in step S30 specifically includes:

[0032] The change of the particle jet top position with time recorded by the high-speed camera is calculated by the imaging method, so as to obtain the particle jet speed.

[0033] A system for characterizing the pressure of a laser plasma flow field, comprising:

[0034] A LIBS system for providing a focused pulsed laser to irradiate a surface of a discrete particle accumulation to generate a laser plasma by laser ablation;

[0035] A high-speed camera for capturing a particle jet formed by acceleration of the particles through the laser plasma flow field;

[0036] A calculation module for calculating the position of the particles in the particle jet recorded by the high-speed camera as a function of time using an imaging method, calculating the velocity of the particles captured by the high-speed camera in the particle jet, obtaining the velocity of the particle jet, and plotting the velocity of the particle jet as a function of the distance from the focal plane to the surface of the particles to characterize the pressure of the laser plasma flow field generated at different distances from the focal plane to the surface of the particles.

[0037] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0038] The present application directly relates the velocity of the particle jet to the pressure of the laser plasma flow field, and provides a convenient, fast, real-time, and in-situ method for characterizing the pressure of the laser plasma flow field generated by laser ablation of a discrete particle accumulation. BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The figure is a flowchart of the method for characterizing the pressure of the laser plasma flow field corresponding to the present application.

[0040] Figure 2 The figure is a curve showing the evolution of the velocity of the top end of the particle jet as a function of the distance from the focal plane of the laser to the surface of the discrete particle accumulation.

[0041] Figure 3 The figure is a schematic diagram of the application scenario of the system for characterizing the pressure of the laser plasma flow field.

[0042] The drawings are only used for illustrative purposes and should not be construed as limiting the present patent; some components in the drawings may be omitted, enlarged, or reduced for better illustration of the embodiments, and do not represent the actual size of the product; it is understandable for those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings; the same or similar reference numerals correspond to the same or similar components; the positional relationship described in the drawings is only used for illustrative purposes and should not be construed as limiting the present patent. DETAILED DESCRIPTION

[0043] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, so that the advantages and features of the present application are more easily understood by those skilled in the art, and the scope of protection of the present application is more clearly defined.

[0044] In the drawings of the embodiments of the present application, the same or similar reference numerals correspond to the same or similar components; in the description of the present application, it should be understood that, if the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "top", "bottom", "inner", "outer" and the like are based on the orientations or positional relationships shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationships in the drawings are only used for exemplary illustration and cannot be understood as a limitation on the present patent.

[0045] In addition, if the terms "first", "second" and the like are used, they are only for descriptive purposes, mainly for distinguishing different devices, elements or components (the specific types and structures may be the same or different), and do not indicate or imply the relative importance and quantity of the devices, elements or components referred to, and cannot be understood as indicating or implying the relative importance.

[0046] Embodiment 1

[0047] To overcome the above-mentioned existing way of measuring the impulse transmitted to the target during the laser ablation process based on the torsional pendulum or the suspended pendulum device to characterize the laser plasma flow field pressure generated when the laser interacts with the hard solid material, which is not suitable for the problem of discrete micro-particle accumulation, the present embodiment discloses a method for characterizing the laser plasma flow field pressure, which is based on the laser-driven particle jet, and the method is suitable for convenient, fast, real-time and in-situ characterization of the laser plasma flow field pressure.

[0048] It should be noted that the surface of the discrete micro-particle accumulation has a certain porosity, and when the laser interacts with it, laser plasma will be generated in the surface layer gap. When the laser plasma flows upward along the direction perpendicular to the target surface at a high speed, due to the existence of the flow field pressure gradient, part of the surface layer particles wrapped in the laser plasma flow field will be directly accelerated by the laser plasma flow field and ejected outward along the direction nearly perpendicular to the particle target surface, forming a macroscopically visible particle jet. The speed of the particle jet should be directly related to the information of the laser plasma flow field pressure, therefore, by measuring the macroscopically visible particle jet, a method for conveniently, quickly, real-time and in-situ characterizing the laser plasma flow field pressure generated when the laser ablates the discrete micro-particle accumulation can be constructed.

[0049] A method for characterizing the laser plasma flow field pressure according to the present embodiment, as shown in Figure 1 includes the following steps:

[0050] S10. Irradiate the surface of the discrete particle accumulation with a pulsed laser to generate laser plasma.

[0051] In this step, the pulsed laser is provided by the LIBS system, and therefore, the step is specifically:

[0052] The surface of the discrete particle accumulation is irradiated by the focused pulsed laser provided by the LIBS system to generate a laser plasma.

[0053] The generation process and principle of the laser plasma are described in the background art, and will not be described in detail here.

[0054] S20. Adjusting the laser parameters to change the pressure of the generated laser plasma flow field, and capturing the particle jet formed by the acceleration of the laser plasma flow field.

[0055] In this step, the laser parameters include the laser wavelength, the laser pulse energy, or the distance from the focal plane to the surface of the discrete particle accumulation, and the particle jet is captured by a high-speed camera, and therefore, the step is specifically:

[0056] By adjusting the laser parameters such as the laser wavelength, the laser pulse energy, or the distance from the focal plane to the surface of the discrete particle accumulation, the pressure of the generated laser plasma flow field is changed, and the particle jet formed by the acceleration of the laser plasma flow field is captured by a high-speed camera.

[0057] S30. Analyzing the captured particle jet to obtain the corresponding particle jet speed or kinetic energy parameters under different laser parameters.

[0058] The step is specifically:

[0059] The captured particle jet is analyzed to calculate the corresponding particle jet speed or kinetic energy parameters under different laser parameters.

[0060] The particle jet speed is obtained by calculating the change of the position of the top of the particle jet recorded by the high-speed camera with time by an imaging method.

[0061] The kinetic energy parameters include:

[0062] The average impact force experienced by the particles captured by the high-speed camera in the particle jet in the flow field, the cross-sectional area of the impact force experienced by the particles captured by the high-speed camera in the particle jet, the average lifetime of the laser plasma flow field, the mass of the particles captured by the high-speed camera in the particle jet, and the speed of the particles captured by the high-speed camera in the particle jet.

[0063] S40. Obtaining the pressure of the laser plasma flow field according to the obtained corresponding particle jet speed or kinetic energy parameters under different laser parameters, to obtain the corresponding relationship between the pressure of the laser plasma flow field and the particle jet speed.

[0064] In this step, the laser plasma flow field pressure is the effect of the particles in the laser plasma flow field on the unit area force, and the effect of the particles in the laser plasma flow field on the unit area force can be represented by the average flow field pressure.

[0065] The average flow field pressure is calculated according to the pressure formula and the law of conservation of energy, combined with the obtained particle jet velocity or kinetic energy parameters corresponding to different laser parameters, that is, the laser plasma flow field pressure is obtained, so that the corresponding relationship between the laser plasma flow field pressure and the particle jet velocity exists.

[0066] In this step, the laser plasma flow field pressure is obtained by the following formula:

[0067]

[0068] Wherein: P is the average flow field pressure, F is the average impact force of the particles captured by the high-speed camera in the particle jet in the flow field, A is the cross-sectional area of the particles captured by the high-speed camera in the particle jet, t is the average lifetime of the laser plasma flow field, is the mass of the particles captured by the high-speed camera in the particle jet, and v is the velocity of the particles captured by the high-speed camera in the particle jet.

[0069] S50. The laser plasma flow field pressure generated under different laser parameters is characterized by the particle jet velocity.

[0070] This step specifically includes:

[0071] The particle jet velocity is used as an observable probe to draw a particle jet velocity curve with laser parameter changes, so as to characterize the laser plasma flow field pressure generated under different laser parameters.

[0072] In this embodiment, the particle jet velocity is directly related to the laser plasma flow field pressure, and by measuring the macroscopically visible particle jet, a method for conveniently, quickly, real-time and in-situ characterizing the laser plasma flow field pressure generated when laser ablation of discrete micro-particle accumulation is constructed.

[0073] Embodiment 2

[0074] This embodiment discloses a method for characterizing the laser plasma flow field pressure, which is based on the method for characterizing the laser plasma flow field pressure in embodiment 1.

[0075] In this embodiment: the particle target formed by the accumulation of glass sand micro-particles is taken as an example to illustrate the method for characterizing the laser plasma flow field pressure described in embodiment 1.

[0076] The following physical principle is used in this embodiment: when other laser parameters remain unchanged, gradually changing the distance between the laser focal plane and the surface of the discrete particle accumulation causes the laser spot irradiating the surface of the discrete particle accumulation to gradually change, which changes the laser flux irradiating the surface of the discrete particle accumulation, and further changes the pressure of the generated laser plasma flow field.

[0077] This embodiment specifically includes the following steps:

[0078] S10. Discrete glass sand with a micron-level size is naturally accumulated in a sample box as a discrete particle accumulation;

[0079] S20. The prepared discrete particle accumulation is placed on a three-dimensional moving platform, and a pulsed laser beam provided by a LIBS system is vertically irradiated onto the surface of the discrete particle accumulation after passing through a focusing lens to generate laser plasma by laser ablation.

[0080] S30. The laser pulse energy and the laser frequency are set to constant values, and the initial position of the surface of the irradiated discrete particle accumulation is set to be several millimeters above the focal plane.

[0081] In the formula, when the focal plane is below the surface of the discrete particle accumulation, the distance between the focal plane and the surface of the discrete particle accumulation is set to a negative value.

[0082] S40. A high-speed camera is used to directly record the particle jet formed by acceleration of the laser plasma flow field; after each laser pulse event, the three-dimensional moving platform is moved in a direction perpendicular to the laser transmission direction to ensure that the subsequent laser pulse acts on the surface area of the discrete particle accumulation that has not been disturbed by the previous laser pulse.

[0083] S50. The three-dimensional moving platform is moved in a direction parallel to the laser transmission direction at a set step to change the distance between the focal plane and the surface of the discrete particle accumulation, thereby simulating different laser plasma flow field conditions; in each simulated laser plasma flow field condition, the particle jet caused by several laser pulses is recorded by the high-speed camera.

[0084] S60. The position of the top end of the particle jet recorded by the high-speed camera is calculated using an imaging method to obtain the velocity of the top end of the particle jet in sequence.

[0085] S70. The velocity of the top end of the particle jet is taken as the vertical coordinate, and the distance between the focal plane and the surface of the discrete particle accumulation is taken as the horizontal coordinate to draw a curve of the velocity of the particle jet with respect to the distance between the focal plane and the surface of the discrete particle accumulation, and the curve is used to represent the pressure of the generated laser plasma flow field under different distances between the focal plane and the surface of the discrete particle accumulation, as shown in Figure 2 The measured values are fitted using the Boltzmann equation in the graph.

[0086] In this embodiment, the particle jet tip velocity is selected as the observable probe of the laser plasma flow field pressure. Other observable probes based on the particle jet can also be used to establish a corresponding relationship with the laser plasma flow field pressure, which will not be described here. In addition, changing other laser parameters can also achieve the modulation of the laser plasma flow field pressure generated by the laser ablation particle accumulation. It should be noted that using any particle jet based on the laser ablation particle accumulation to characterize the corresponding laser plasma flow field pressure is within the scope of this patent.

[0087] Embodiment 3

[0088] This embodiment discloses a laser plasma flow field pressure characterization system, which uses the laser plasma flow field pressure characterization method of embodiment 1 or embodiment 2 to characterize the laser plasma flow field pressure conveniently, quickly, in real time and in situ.

[0089] The laser plasma flow field pressure characterization system disclosed in this embodiment, as shown in Figure 3 includes a LIBS system 1, a high-speed camera 4, and a calculation module 5.

[0090] The LIBS system 1 is used to provide a focused pulsed laser 2 to irradiate the surface of a discrete particle accumulation 3, and generate a laser plasma by ablation of the focused pulsed laser 2.

[0091] The discrete particle accumulation 3 is a sample to be measured, which is used to generate a laser plasma under the irradiation of the focused pulsed laser 2.

[0092] The high-speed camera 4 is used to capture and record the particle jet formed by the laser plasma flow field acceleration.

[0093] The calculation module 5 uses imaging methods to calculate the position of the particles in the particle jet recorded by the high-speed camera 4 with time, calculates the particle velocity of the particles captured by the high-speed camera in the particle jet, obtains the particle jet velocity, and draws the curve of the particle jet velocity with the distance from the focal plane to the particle surface, to characterize the laser plasma flow field pressure generated at different distances from the focal plane to the particle surface.

[0094] The specific implementation process of this example is described in embodiment 1 or embodiment 2, and this embodiment will not be described in more detail.

[0095] Obviously, the above embodiments of the present application are merely exemplary but not intended to limit the embodiments of the present application. Based on the above description, any other variations or changes can be made by those skilled in the art without departing from the spirit and principles of the present application. It is not necessary to list all the embodiments here. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall fall within the scope of the claims of the present application.

Claims

1. A method for characterizing the pressure of a laser plasma flow field, characterized in that, Including the following steps: S10. Laser plasma is generated by irradiating the surface of a discrete particle stack with a pulsed laser. S20. Adjust the laser parameters to change the pressure of the generated laser plasma flow field and capture the particle jets formed by the acceleration of the laser plasma flow field; S30. Analyze the captured particle jet to obtain the particle jet velocity or kinetic energy parameters corresponding to different laser parameters; S40. Obtain the laser plasma flow field pressure based on the particle jet velocity or kinetic energy parameters corresponding to different laser parameters, so as to obtain the correspondence between the laser plasma flow field pressure and the particle jet velocity; S50. The pressure of the laser plasma flow field generated under different laser parameters is characterized by the particle jet velocity.

2. The method for characterizing the pressure of a laser plasma flow field according to claim 1, characterized in that, In step S20, the capture of the particle jet specifically involves: The particle jets formed by the acceleration of the laser plasma flow field are captured by a high-speed camera.

3. The method for characterizing the pressure of a laser plasma flow field according to claim 2, characterized in that, In step S30, the kinetic energy parameters include: The average impact force experienced by particles captured by a high-speed camera in a particle jet within the flow field; the cross-sectional area of ​​the particles captured by a high-speed camera in a particle jet experiencing the impact force; the average lifetime of the laser plasma flow field; the mass of particles captured by a high-speed camera in a particle jet; and the velocity of particles captured by a high-speed camera in a particle jet.

4. The method for characterizing the pressure of a laser plasma flow field according to claim 3, characterized in that, Step S40 specifically includes: Based on the pressure formula and the law of conservation of energy, and combined with the particle jet velocity or kinetic energy parameters obtained under different laser parameters, the pressure of the laser plasma flow field is obtained, thus revealing the correspondence between the laser plasma flow field pressure and the particle jet velocity.

5. The method for characterizing the pressure of a laser plasma flow field according to claim 4, characterized in that, The laser plasma flow field pressure is the effect of the force per unit area on the particles in the laser plasma flow field, and the effect of the force per unit area on the particles in the laser plasma flow field can be expressed by the average flow field pressure. The pressure of the laser plasma flow field is obtained by the following formula: Where: P represents the average flow field pressure, F represents the average impact force felt by the particles captured by the high-speed camera in the particle jet, A represents the cross-sectional area of ​​the particles captured by the high-speed camera in the particle jet that feel the impact force, t represents the average lifetime of the laser plasma flow field, m represents the mass of the particles captured by the high-speed camera in the particle jet, and v represents the velocity of the particles captured by the high-speed camera in the particle jet.

6. The method for characterizing the pressure of a laser plasma flow field according to claim 1, characterized in that, Step S50 specifically includes: Using particle jet velocity as an observable probe, the curves of particle jet velocity versus laser parameters were plotted to characterize the pressure of the laser plasma flow field generated under different laser parameters.

7. The method for characterizing the pressure of a laser plasma flow field according to claim 1, characterized in that, The laser parameters specifically include: Laser wavelength, laser pulse energy, or distance from the focal plane to the surface of the discrete particle accumulation.

8. The method for characterizing the pressure of a laser plasma flow field according to claim 1, characterized in that, Step S10 specifically includes: The surface of a discrete particle deposit is irradiated with a focused pulsed laser provided by the LIBS system to generate laser plasma.

9. The method for characterizing the pressure of a laser plasma flow field according to claim 2, characterized in that, The specific steps for obtaining the particle jet velocity in step S30 include: The particle jet velocity is obtained by calculating the change in the position of the tip of the particle jet recorded by a high-speed camera over time using imaging methods.

10. A system for characterizing the pressure of a laser plasma flow field, characterized in that, include: The LIBS system is used to provide focused pulsed laser light to irradiate the surface of discrete particle deposits, generating laser plasma through laser ablation. High-speed camera used to capture and record particle jets formed by acceleration through a laser plasma flow field; The calculation module uses imaging methods to calculate the change of particle position in the particle jet recorded by the high-speed camera over time, calculates the velocity of the particles captured by the high-speed camera in the particle jet, obtains the particle jet velocity, and plots the change curve of particle jet velocity with the distance from the focal plane to the particle surface to characterize the pressure of the laser plasma flow field generated at different distances from the focal plane to the particle surface.

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