Method and device for measuring deposited energy in femtosecond laser cloud penetration and fog penetration process

Abstract

The application relates to a femtosecond laser cloud-penetrating-mist deposition energy measurement method and device, which obtains a lateral shadow map of a plasma light wire in an orthogonal view angle and an acousto-optic signal map at different positions; for the lateral shadow map, shadow method is adopted to obtain shape profile information of the plasma light wire, so that a lateral cross-section map is obtained; for the acousto-optic signal map at different positions, a back projection algorithm is adopted to calculate energy absorption distribution information of the plasma light wire, so that a transverse cross-section map is obtained; finally, based on an image fusion method, the lateral cross-section map and the transverse cross-section map are fused and processed, so that a three-dimensional deposition energy distribution map of the plasma light wire is obtained. The method provides a measurement method with good reliability, convenient operation and high resolution for three-dimensional deposition energy distribution of a femtosecond laser plasma light wire.

Description

Technical Field

[0001] This application relates to the field of interdisciplinary application technology of optical physics and atmospheric science, and in particular to a method and device for measuring deposition energy during the process of femtosecond laser penetration of clouds and fog. Background Technology

[0002] Laser filamentation is a special phenomenon formed by the nonlinear propagation of high-power femtosecond laser pulses in an optical medium. Femtosecond filamentation for weather modification is a relatively new technology that has emerged in recent years. In particular, the "cleaning" function of femtosecond lasers during cloud and fog penetration has significant potential applications in optical waveguides, assisted laser communication, and guiding radio frequency signal transmission. Therefore, conducting relevant basic research and application exploration is of great importance to promoting the application of this technology.

[0003] Existing research indicates that the "cleaning" function of femtosecond lasers penetrating clouds and fog is related to the rapid thermal expansion of the filament region caused by the thermal deposition energy of the filament. Accurately measuring the density distribution of deposited energy in the filament region is crucial for estimating gas density evolution, cloud particle displacement amplitude, and channel duration. However, due to the extremely short timescale (~ns) and small spatial scale (~μm) of the accompanying physical processes in the filament, direct measurement of the energy deposition density within the filament has always been very difficult.

[0004] During femtosecond optical filament propagation, a sharp, piercing sound is typically heard. This is due to the instantaneous compression of surrounding air by the thermal expansion of the energy deposited in the filament, resulting in ultrasonic wave attenuation on a microsecond (μs) timescale. The intensity of the acoustic signal generated by the filament is closely related to the density of energy deposition. Therefore, detecting this acoustic signal could potentially reveal information about the energy distribution within the filament. Researchers have used micromicrophones to measure the acoustic signal intensity, thereby indirectly obtaining the linear energy deposition rate of the filament; however, this method cannot reveal the spatial structure within the filament. Summary of the Invention

[0005] Therefore, it is necessary to address the aforementioned technical problems by providing a method and apparatus for measuring the deposition energy during femtosecond laser penetration through clouds and fog, capable of reconstructing a three-dimensional structural image of the filaments formed by a femtosecond laser in air and cloud / fog environments. A method for measuring deposition energy during femtosecond laser penetration of clouds and fog, the method comprising: Obtain the lateral shadow map of the plasma filament under orthogonal viewpoints and the acousto-optic signal map at different positions along the transmission direction of the plasma filament; Based on the lateral shadow map, the shape contour information of the plasma filament is obtained, and a lateral cross-sectional view is obtained; Based on the acousto-optic signal maps at different locations, the energy absorption distribution information of the plasma filament is calculated to obtain a transverse cross-sectional view; The lateral cross-sectional image and the transverse cross-sectional image are fused to obtain a three-dimensional deposition energy distribution map of plasma filaments.

[0006] In one embodiment, based on the lateral shadow map, the shape contour information of the plasma filament is obtained by using the shadow method to obtain a lateral cross-sectional view. .

[0007] In one embodiment, based on the acousto-optic signal maps at different locations, the energy absorption distribution information of the plasma filament is calculated using a back-projection algorithm to obtain a transverse cross-sectional view.

[0008] The energy absorption distribution information of the plasma filament is calculated using a back-projection algorithm to obtain a transverse cross-sectional view, including: The acoustic-optic signal maps at different locations are reconstructed using a back-projection algorithm, and the energy distribution information of the plasma filament is calculated to obtain a two-dimensional initial sound pressure intensity distribution map of the plasma filament. Based on the pressure-energy relationship, the initial two-dimensional sound pressure intensity distribution map is converted into a two-dimensional optical filament cross-section energy absorption distribution, resulting in transverse cross-sectional diagrams at different locations. .

[0009] In one embodiment, the expression for the back-projection algorithm is: ; In the formula, for The reconstructed sound pressure level at the location. This represents the distance from the scan center point to the reconstructed pixel. Indicates the scan center point to the th The distance between transducers Indicates the back projection term. Represents the solid angle weighting factor. For the entire measurement surface Relative to its interior Solid angle of position reconstruction Transducer surface detection unit Compared to Solid angle of the reconstructed location point This indicates the speed of sound in an adiabatic environment.

[0010] In one embodiment, the pressure-energy relationship is expressed as: ; in, This represents the initial sound pressure intensity distribution. This represents the initial absorbed energy distribution. The initial absorbed energy distribution map Transform into Cartesian coordinate system .

[0011] In one embodiment, the lateral cross-sectional image and the transverse cross-sectional image are fused using an image fusion method to obtain a three-dimensional deposition energy distribution map of the plasma filament, including: According to the Cross-sectional view obtained from the acoustic-optical data detected by the transducer array ,Will Non-zero boundary values ​​as The outer boundary profile of the plasma filament cross-section at that location; According to the lateral section diagram The shape of the plasma filament is obtained along... Width information in direction and along Length information in the direction; Lateral section diagram In Sectional views and multiple transverse section views In The cross-sectional view uses a convolutional neural network model to extract features, mapping the view features within a set of viewpoints to a new feature to obtain the view features; The view features are fused using a feature point matching method or a multilayer perceptron method to obtain the three-dimensional deposition energy distribution feature data of the plasma filament. ; The three-dimensional deposition energy distribution characteristic data A view rendering was performed to obtain a three-dimensional deposition energy distribution map of the plasma filament.

[0012] A device for measuring the deposition energy during femtosecond laser penetration of clouds and fog, the device comprising: Main hull; A cloud and fog generating component is disposed around the main body and connected to the main body via a channel. An acousto-optic signal acquisition component is installed inside and around the main cabin. It emits a femtosecond laser, focuses it inside the main cabin to form a plasma filament, and obtains the acousto-optic signal map of the plasma filament. A lateral shadowing acquisition component, positioned around the main cabin, acquires a lateral shadowing map of the plasma filament by emitting pulsed laser light.

[0013] In one embodiment, the main cabin is a cavity structure with a first light-transmitting hole, a second light-transmitting hole, a third light-transmitting hole and a fourth light-transmitting hole. The first light-transmitting aperture and the second light-transmitting aperture are arranged opposite to each other to allow the femtosecond laser to pass through; The third light-transmitting aperture is positioned opposite to the fourth light-transmitting aperture to allow the pulsed laser to pass through.

[0014] In one embodiment, the acousto-optic signal acquisition component includes: A femtosecond laser is positioned around the main cabin body to generate femtosecond lasers; A first reflecting mirror is disposed in the optical path of the femtosecond laser to change the direction of the femtosecond laser so that it passes through the first through hole of the main body; A focusing lens is disposed between the first reflector and the main body, and is located in the optical path of the femtosecond laser; A beam collector is disposed near the second through-hole of the main body and located in the optical path of the femtosecond laser to intercept the femtosecond laser emitted from the second through-hole; The photoacoustic measurement unit is fixed inside the main cabin and is set parallel to the transmission direction of the femtosecond laser. It is used to collect the acoustic signals generated at different positions along the transmission direction of the plasma filament formed by the femtosecond laser inside the main cabin.

[0015] In one embodiment, the photoacoustic measurement unit includes a ridge-type ultrasonic transducer array, a lifting boom, a top slide rail, and a multi-channel data acquisition card; A spine-type ultrasonic transducer array is disposed within the cavity of the main body and parallel to the transmission direction of the plasma filament, in order to acquire photoacoustic signals generated at different positions of the plasma filament; The lifting boom includes a first connecting rod and a second connecting rod. The spine-type ultrasonic transducer array is arranged on the first connecting rod. One end of the second connecting rod is vertically fixed to the first connecting rod, and the other end is connected to the top slide rail for adjusting the height of the spine-type ultrasonic transducer array. The top slide rail is fixed on the inner wall of the main cabin cavity along the transmission direction of the plasma filament, and is connected to the spine-type ultrasonic transducer array through a lifting rod, for adjusting the horizontal position of the spine-type ultrasonic transducer array; The multi-channel data acquisition card is electrically connected to the spine-type ultrasonic transducer array and is used to acquire the photoacoustic signal.

[0016] In one embodiment, the spine-type ultrasonic transducer array includes a plurality of transducers arranged in an array. The transducers are arc-shaped, and the inner arc surface has a plurality of uniformly arranged ultrasonic transducer elements.

[0017] In one embodiment, the lateral shadow map acquisition component includes: A pulsed laser, positioned around the main cabin, is used to generate pulsed laser light. The second reflector is used to change the direction of the pulsed laser so that it passes through the third light-transmitting hole of the main body; A diffuser plate, disposed between the second reflector and the third light-transmitting hole, is used to scatter the pulsed laser beam, thereby uniformly irradiating the plasma interaction area; A filter is disposed near the fourth light-passing hole to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament; A neutral density filter is placed behind the optical filter to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament. A camera, positioned behind the neutral density filter, is used to capture the lateral shadow image. The second reflector, the diffuser, the filter, the neutral density filter, and the camera are all located in the optical path of the pulsed laser.

[0018] In one embodiment, the device further includes a timing controller and a computer; The timing controller is electrically connected to the camera, pulsed laser, and femtosecond laser. It is used to receive the trigger signal emitted by the femtosecond laser and send it to the multi-channel data acquisition card, and start the multi-channel data acquisition card, the pulsed laser, and the camera to work after a set delay. The computer is located around the main cabin and is electrically connected to the femtosecond laser and the multi-channel data acquisition card. It is used to monitor and display the working status of the femtosecond laser and the pulsed laser, the coordination between different component units, the storage and analysis of data, and the timing controller to transmit and receive signals.

[0019] In one embodiment, the cloud generating component includes an atomizer and an air pump; The main body is provided with an air inlet and an air outlet. The atomizer is located on one side of the air inlet and is connected to the air inlet through a channel. The air pump is located on one side of the air outlet and is connected to the air outlet through a channel.

[0020] The aforementioned method and apparatus for measuring deposition energy during femtosecond laser penetration of clouds and fog involves acquiring lateral shadow images of the plasma filament from orthogonal perspectives and acousto-optic signal images at different locations. For the lateral shadow images, a shadow method is used to obtain the shape and contour information of the plasma filament, resulting in a lateral cross-sectional image. For the acousto-optic signal images at different locations, a back-projection algorithm is used to calculate the energy absorption distribution information of the plasma filament, resulting in a transverse cross-sectional image. Finally, an image fusion method is used to fuse the lateral cross-sectional image and the transverse cross-sectional image to obtain a three-dimensional deposition energy distribution map of the plasma filament.

[0021] This invention fully utilizes the high resolution of optical imaging and the high penetration of acoustic imaging to obtain two-dimensional cross-sectional information of the plasma filament from two orthogonal viewing angles. This allows for the reconstruction of the three-dimensional deposition energy distribution of the femtosecond laser-formed filament in air and cloud / fog environments using image fusion. This provides a reliable, convenient, and high-resolution measurement method for the three-dimensional deposition energy distribution of femtosecond laser plasma filaments. Furthermore, by controlling the movement of the fog-laden airflow, experimental conditions closer to actual cloud / fog environments can be generated. The device is simple in structure, easy to operate, highly precise in control, and highly practical. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the deposition energy measurement method during the femtosecond laser cloud penetration and fog penetration process provided in Example 1; Figure 2 This is a schematic diagram of orthogonal dual-view coordinates provided in Example 1; Figure 3 This is a schematic diagram of the initial two-dimensional acoustic pressure intensity distribution of a single filament of a plasma filament reconstructed using a back-projection algorithm, as provided in Example 1. Figure 4 This is a schematic diagram of the multi-filament two-dimensional initial acoustic pressure intensity distribution of the plasma filament reconstructed using the back-projection algorithm, as provided in Example 1. Figure 5 This is a structural diagram of the deposition energy measurement device during the femtosecond laser cloud and fog penetration process provided in Example 2; Figure 6 This is a schematic diagram of a single semi-circular arc-shaped ultrasonic transducer array structure provided in Example 2; Figure 7 This is a schematic diagram of the photoacoustic signal distribution obtained by simulating a single arc-shaped array of ultrasonic transducers provided in Example 2; Explanation of reference numerals in the attached figures: Femtosecond laser 1, first reflector 2, focusing lens 3, first light-transmitting aperture 4, second light-transmitting aperture 5, beam collector 6, timing controller 7, pulsed laser 8, second reflector 9, diffuser 10, third light-transmitting aperture 111, fourth light-transmitting aperture 112, filter 12, neutral density filter 13, camera 14, spine-type ultrasonic transducer array 15, transducer 151, transducer array element 152, lifting boom 16, top slide rail 17, multi-channel data acquisition card 18, computer 19, atomizer 20, air inlet 21, main cabin 22, air outlet 23, air pump 24. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0024] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0025] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly and specifically defined.

[0026] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0027] Example 1 See Figure 1 The present invention provides a method for measuring the deposition energy during femtosecond laser penetration of clouds and fog, comprising the following steps: Step 102: Take the lateral shadow map of the plasma filament under orthogonal viewing angle and the acousto-optic signal map at different positions along the transmission direction of the plasma filament.

[0028] It can be understood that the final result of this embodiment is a three-dimensional structure diagram, i.e., the coordinate system is... Therefore, the lateral two-dimensional cross-sectional view and the transverse two-dimensional cross-sectional view under orthogonal viewing angles are first obtained using a measuring device. These are lateral shadow images and an acoustic-optical signal image, which are two-dimensional images with different coordinate systems. The coordinate system representation of this two-dimensional image varies depending on the placement of the measuring device. (See also...) Figure 2 This is a schematic diagram of orthogonal dual-view coordinates provided in this embodiment. This schematic diagram is only for the purpose of understanding the coordinate system set in this application and is not intended to limit the specific solution.

[0029] Acquiring acousto-optic signals at different locations along the plasma filament propagation direction is of great significance for better understanding plasma characteristics, regulating and controlling plasma processes, studying plasma physics, and monitoring and diagnosing faults. This information can help improve the performance of plasma devices, optimize plasma processes, and enhance our understanding of plasma science.

[0030] Furthermore, the lateral shadow map and acoustic-optic signal map obtained here include two cases: one is the lateral shadow map and acoustic-optic signal map obtained without cloud and fog interference, and the other is the lateral shadow map and acoustic-optic signal map obtained with cloud and fog interference. Using this method, three-dimensional deposition energy distribution maps of plasma filaments under cloudless and cloud-interference environments are constructed respectively. Then, the differences in the three-dimensional distribution of filament deposition energy under cloudless and cloud-interference conditions are compared to study the differences in plasma filaments formed with and without clouds and fog.

[0031] Step 104: Based on the lateral shadow map, obtain the shape contour information of the plasma filament to obtain the lateral cross-sectional view.

[0032] It is understandable that, based on the principles of light diffraction and shadow formation, the shape and contour of a plasma filament can be inferred by observing its shadow and analyzing its shape and changes. This embodiment uses the shadow method to obtain the shape and contour information of the plasma filament.

[0033] In one embodiment, the shape and contour information of the plasma filament is obtained by using a shadowing method to obtain a lateral cross-sectional view. .

[0034] Specifically, the region of gas molecule density perturbation caused by the plasma filament is obtained from the stripe distribution in the lateral shadow map, and this region is considered as the plasma along... By projecting the cross section in the direction, the corresponding lateral cross section diagram is obtained. .

[0035] Step 106: Based on the acousto-optic signal maps at different locations, calculate the energy absorption distribution information of the plasma filament to obtain a transverse cross-sectional view.

[0036] It is understandable that the back projection algorithm can project the acoustic-optical signal images at different locations back onto each pixel position on the image plane in order to reconstruct the original image.

[0037] In one embodiment, the energy absorption distribution information of the plasma filament is calculated by a back-projection algorithm to obtain a transverse cross-sectional view.

[0038] Specifically, the acoustic-optic signal maps at different locations are reconstructed using a back-projection algorithm to calculate the energy distribution information of the plasma filament, thus obtaining a two-dimensional initial acoustic pressure intensity distribution map of the plasma filament. Then, based on the pressure-energy relationship, the two-dimensional initial acoustic pressure intensity distribution map is converted into a two-dimensional cross-sectional energy absorption distribution of the filament, resulting in transverse cross-sectional maps at different locations. .

[0039] More specifically, the expression for the back projection algorithm is: ; in: ; ; In the formula, for The reconstructed sound pressure level at the location. This represents the distance from the scan center point to the reconstructed pixel. Indicates the scan center point to the th The distance between transducers Indicates the back projection term. Indicates the first The acoustic signal received by each transducer Represents the solid angle weighting factor. For the entire measurement surface Relative to its interior The solid angle for position reconstruction, for a plane For spheres and cylinders , Transducer surface detection unit Compared to Solid angle of the reconstructed location point This represents the adiabatic speed of sound. It's worth noting that the entire measurement surface mentioned here... This refers to the transducer surface, and the transducer surface detection unit. It refers to the micro-elements on the receiving surface of the transducer.

[0040] See Figure 3 This embodiment provides a two-dimensional initial sound pressure intensity distribution map of a single plasma filament reconstructed using a back-projection algorithm. The initial sound pressure intensity distribution must satisfy the following expression: ; In the formula, Indicates the coefficient of thermal expansion. This indicates the specific heat capacity of air at constant volume. This represents the maximum energy of pulse deposition per unit volume. This represents the distance between the signal receiving point and the coordinate center. This represents the Gaussian radius of the heat source distribution in the optical filament. In the two-dimensional initial sound pressure intensity distribution diagram of the single filament... , , , , .

[0041] See Figure 4 This is a two-dimensional initial acoustic pressure intensity distribution map of a multi-filament plasma filament reconstructed using a back-projection algorithm, provided in this embodiment. The maximum energy per unit volume of pulse deposition in the central master filament is shown. Gaussian radius of heat source distribution The maximum energy per unit volume of pulse deposition for the left and right accessory filaments Gaussian radius of heat source distribution As can be seen from the figure, photoacoustic tomography can reconstruct multi-filament cross-sectional images quite well.

[0042] More specifically, the relationship between pressure and energy can be expressed as follows: ; in, This represents the initial sound pressure intensity distribution. This shows the initial absorbed energy distribution map, and then the initial absorbed energy distribution map... Convert to Cartesian coordinate system This yields the cross-sectional view. By reconstructing in this way, cross-sectional views at different locations can be obtained. .

[0043] Step 108: The lateral section image and the transverse section image are fused to obtain a three-dimensional deposition energy distribution map of plasma filaments.

[0044] It is understandable that this is due to the multiple cross-sectional views obtained. and lateral section diagram All images are two-dimensional. To obtain a three-dimensional deposition energy distribution map of plasma filaments, the two-dimensional images need to be processed.

[0045] In one embodiment, an image fusion method is used to fuse the lateral section image and the transverse section image. Specifically, according to the first Cross-sectional view obtained from the acoustic-optical data detected by the transducer array ,Will Non-zero boundary values ​​as The outer boundary profile of the plasma filament cross-section at that location; According to the lateral section diagram The shape of the plasma filament is obtained along... Width information in direction and along Length information in the direction; Lateral section diagram In Sectional views and multiple transverse section views In The cross-sectional view uses a convolutional neural network model to extract features, mapping the view features within a set of viewpoints to a new feature to obtain the view features; The view features are fused using a feature point matching method or a multilayer perceptron method to obtain the three-dimensional deposition energy distribution feature data of the plasma filament. ; Three-dimensional deposition energy distribution characteristic data A view rendering was performed to obtain a three-dimensional deposition energy distribution map of the plasma filament.

[0046] The aforementioned method for measuring deposition energy during femtosecond laser penetration of clouds and fog involves acquiring lateral shadow maps of the plasma filament from orthogonal perspectives and acousto-optic signal maps at different locations. For the lateral shadow map, a shadow method is used to obtain the shape and contour information of the plasma filament, resulting in a lateral cross-sectional map. For the acousto-optic signal maps at different locations, a back-projection algorithm is used to calculate the energy absorption distribution information of the plasma filament, resulting in a transverse cross-sectional map. Finally, an image fusion method is used to fuse the lateral cross-sectional map and the transverse cross-sectional map to obtain a three-dimensional deposition energy distribution map of the plasma filament.

[0047] The method provided in this embodiment fully utilizes the high resolution of optical imaging and the high penetration of acoustic imaging to obtain two-dimensional cross-sectional information of the plasma filament from two orthogonal perspectives. Thus, the three-dimensional deposition energy distribution of the femtosecond laser forming the filament in air and cloud environments is reconstructed using image fusion. This provides a reliable, convenient, and high-resolution measurement method for the three-dimensional deposition energy distribution of femtosecond laser plasma filaments.

[0048] It should be understood that, although Figure 1 The steps in the flowchart are shown sequentially as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order in which these steps are executed, and they can be performed in other orders. Figure 1 At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0049] Example 2 See Figure 5 and 6 The structure of the deposition energy measurement device for the femtosecond laser cloud penetration and fog penetration process provided in this embodiment includes a main chamber 22, a cloud and fog generation component, an acoustic-optic signal acquisition component, a lateral shadow map acquisition component, and a computer 19. The main chamber 22 is a three-dimensional structure with a sealed cavity, which can be designed according to requirements, such as a cube, cuboid, or cylinder. The cloud and fog generation component is located on the periphery of the main chamber 22 and is connected to the main chamber 22 through a channel; the acoustic-optic signal acquisition component is located inside and around the main chamber 22, and by emitting a femtosecond laser, it focuses the plasma filament inside the main chamber 22 to form a plasma filament and obtain the acoustic-optic signal map of the plasma filament; the lateral shadow map acquisition component is located around the main chamber 22, and by emitting pulsed lasers, it obtains the lateral shadow map of the plasma filament.

[0050] Specifically, the main cabin 22 is a cavity structure with a first light-transmitting hole 4, a second light-transmitting hole 5, a third light-transmitting hole 111, and a fourth light-transmitting hole 112. All light-transmitting holes are sealed with quartz glass. The first light-transmitting hole 4 and the second light-transmitting hole 5 are arranged opposite each other to allow femtosecond lasers to pass through. The third light-transmitting hole 111 and the fourth light-transmitting hole 112 are arranged opposite each other to allow pulsed lasers to pass through. For example, in this embodiment, the first light-transmitting hole 4 and the second light-transmitting hole 5 are located on the left and right sides, and in order to form an orthogonal viewing angle, the third light-transmitting hole 111 and the fourth light-transmitting hole 112 are located on the front and rear sides.

[0051] An air inlet 21 and an air outlet 23 are also provided on the main cabin 22. The air inlet 21 and the air outlet 23 are positioned opposite each other, with the air inlet 21 located at the lower part of the main cabin 22 and the air outlet 23 located at the upper part of the main cabin 22. For example, in this embodiment, the air inlet 21 is located at the lower left side of the main cabin 22 and the air outlet 23 is located at the upper right side of the main cabin 22, so that the fog generated by the fog generating component can enter the main cabin 22 from the air inlet 21 and flow out from the air outlet 23 to form a flowing fog environment.

[0052] The acousto-optic signal acquisition component includes a femtosecond laser 1, a first reflecting mirror 2, a focusing lens 3, a beam collector 6, and a photoacoustic measurement unit. The femtosecond laser 1 is positioned around the main chamber 22 to generate the femtosecond laser. The first reflecting mirror 2 is positioned in the optical path of the femtosecond laser to change its direction, allowing it to pass through the first through-hole 4 of the main chamber 22. The focusing lens 3 is positioned between the first reflecting mirror 2 and the main chamber 22, and is located in the optical path of the femtosecond laser for focusing. The beam collector 6 is positioned on the opposite side of the first through-hole 4, near the second through-hole 5. The beam collector 6 is also located in the optical path of the femtosecond laser, intercepting the femtosecond laser as it exits from the first through-hole 4 and the second through-hole 5.

[0053] The photoacoustic measurement unit includes a spine-type ultrasonic transducer array 15, a lifting boom 16, a top slide rail 17, and a multi-channel data acquisition card 18. The spine-type ultrasonic transducer array 15 is housed within the cavity of the main chamber 22 and consists of several transducers 151, each parallel to the transmission direction of the plasma filament, used to acquire photoacoustic signals generated at different positions of the plasma filament. The lifting boom 16 includes a first connecting rod and a second connecting rod. The transducer array is arranged on the first connecting rod, and one end of the second connecting rod is vertically fixed to the first connecting rod, while the other end is connected to the top slide rail 17. The lifting boom 16 controls the raising and lowering of the array to adjust its height. The top slide rail 17 is fixed to the inner wall of the cavity of the main chamber 22 along the transmission direction of the plasma filament and is connected to the transducers 15 via the lifting boom 16. Adjusting the horizontal movement of the top slide rail 17 adjusts the movement of the transducers 15 along the transmission direction of the plasma filament, thus improving the acquisition of photoacoustic signals. The multi-channel data acquisition card 18 is electrically connected to the transducer 15 and is used to acquire photoacoustic signals.

[0054] The transducer 151 is arc-shaped, and is composed of several transducer array elements 152 evenly arranged on it. It can simultaneously record photoacoustic signals at multiple locations along the femtosecond laser transmission direction, providing more information for the reconstruction of the three-dimensional structure of the plasma filament. It is worth noting that the axis of the spine-type ultrasonic transducer array 15 is in the same vertical plane as the femtosecond laser transmission direction during measurement. Therefore, the position of the photoacoustic measurement unit can be set according to actual conditions. In this embodiment, the photoacoustic measurement unit is placed on the top of the inner wall of the main chamber 22, also to meet the condition of being in the same vertical plane as the femtosecond laser transmission direction during measurement. (See reference...) Figure 7 The acoustic field distribution of an arc-shaped transducer array consisting of 40 transducers is provided, wherein the arc of the semi-ring is 180°, the center frequency of each transducer is 2.0 MHz, the bandwidth is 70%, and 40dB of noise is added to the acoustic signal.

[0055] More specifically, the lifting boom 16 has a hollow structure inside, which is used to house the signal line of the transducer 15.

[0056] It is worth noting that the laser pulse generated by the femtosecond laser 1 passes sequentially through the first reflecting mirror 2, the focusing lens 3, and the first light-transmitting aperture 4 before entering the main chamber 22. It then exits through the second light-transmitting aperture 5 and is intercepted by the beam collector 6. By adjusting the position of the focusing lens 3, the position of the plasma filament generated by the femtosecond laser within the main chamber 22 can also be adjusted. Replacing the beam collector with a Joule meter / power meter allows for the determination of the energy of the emitted femtosecond laser beam. The difference between this energy and the incident laser beam energy yields the total attenuated laser pulse energy.

[0057] Under the action of a femtosecond laser plasma filament, the laser energy absorbed by the ionization of the medium is radiated in the form of fluorescence, harmonics, etc., and released in the form of thermal deposition. The instantaneous thermal expansion compresses the surrounding air, generating ultrasonic waves / sound waves under the action of thermoelasticity. The spine-type ultrasonic transducer array 15 located directly above the filament receives the acoustic signal excited by the filament, which is acquired by the multi-channel data acquisition card 18 and transmitted to the computer 19 for storage and image reconstruction.

[0058] The lateral shadow mapping assembly includes a pulsed laser 8, a second reflector 9, a diffuser 10, a filter 12, a neutral density filter 13, and a camera 14, all positioned around the main chamber 22. When placed, the second reflector 9, diffuser 10, filter 12, neutral density filter 13, and camera 14 are all located in the optical path of the pulsed laser. The pulsed laser 8 generates the pulsed laser beam. The second reflector 9 changes the direction of the pulsed laser beam, directing it through the third aperture 111 of the main chamber 22. The diffuser 10 is positioned between the second reflector 9 and the third aperture 111 to scatter the pulsed laser beam, thereby uniformly illuminating the plasma interaction area. A filter 12 is positioned near the fourth aperture 112 to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament. A neutral density filter 13 is positioned behind the filter 12, also to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament. A camera 14 is positioned behind the neutral density filter 13 to capture the lateral shadow image; preferably, a CCD camera or a CMOS camera is used. The lateral shadow image acquisition component is used to obtain a lateral cross-sectional image of the plasma filament in a direction orthogonal to the femtosecond laser transmission direction, thereby analyzing the lateral boundary of the plasma filament.

[0059] It is worth noting that under the action of the femtosecond laser plasma filament, the air expands and its density changes. The probe beam emitted by the pulsed laser 8, after passing through the second reflector 9, is scattered on the diffuser plate 10 and enters the main chamber 22 through the third light-transmitting hole 111. After passing through the plasma filament region, it passes through the fourth light-transmitting hole 112, the filter 12, and the neutral density attenuator 13. Due to the change in air density, an optical path difference is generated, forming a lateral shadow image that is projected onto the rear camera 14. The timing controller 7 is used to receive the femtosecond laser pulse trigger signal and control the pulsed laser 8 to emit pulsed laser according to the set interval time. Since the change in spatial medium density caused by the plasma filament occurs within a very short time after the femtosecond laser pulse transmission, the exposure time of the camera 14 must also be adjusted by the timing controller 7. The camera 14 should have an external trigger adjustment function, and the minimum gate width should be at the nanosecond level. The femtosecond laser 1 emits a trigger signal, the timing controller 7 receives the trigger signal, and according to the set delay, starts the exposure operation of the pulsed laser 8 and the camera 14, recording the corresponding lateral shadow image. To reduce the interference of stray light and plasma filament autofluorescence on the side-shadow image, a filter 12 with the same wavelength as the probe light and a neutral density attenuator 13 are added in front of the camera. The fringe distribution in the side-shadow image reveals the region of medium density variation caused by the plasma, which can be considered as the plasma along... The projection section in the direction, and the corresponding projected area is The corresponding coordinate system is as follows: Figure 2 As shown. Above In one embodiment, a timing controller 7 and a computer 19 are also included; The timing controller 7 is electrically connected to the camera 14, the pulsed laser 8 and the femtosecond laser 1. It is used to receive the trigger signal emitted by the femtosecond laser 1 and send it to the multi-channel data acquisition card 18, and start the multi-channel data acquisition card 18, the pulsed laser 8 and the camera 14 to work after a set delay. Computer 19 is located around the main cabin 22 and is electrically connected to femtosecond laser 1 and multi-channel data acquisition card 18. It is used to monitor and display the working status of femtosecond laser 1 and pulsed laser 8, the coordination between different component units, data storage and analysis, and the timing controller to transmit and receive signals.

[0060] The cloud-generating component includes an atomizer 20 and an air pump 24. The atomizer 20 is located on one side of the air inlet 21 and connected to the air inlet 21 via a channel. The air pump is located on one side of the air outlet 22 and connected to the air outlet via a channel. When the atomizer 20 is turned on, the mist enters the main chamber 22 through the air inlet 21 and gradually diffuses throughout the entire chamber, then flows out through the air outlet 23, creating a fluid cloud-like environment. The atomizer 20 is preferably an ultrasonic atomizer.

[0061] In one embodiment, the operation of the deposition energy measurement device during the entire femtosecond laser cloud-penetrating and fog-penetrating process is as follows: Step 201: Turn on the femtosecond laser 1, emit the femtosecond laser, adjust the position of the focusing lens so that the femtosecond laser pulse enters from the first through hole 4 and forms a plasma filament in the middle of the cavity of the main chamber 22.

[0062] Step 202: Move the spine-type ultrasonic transducer array 15 to a position above the plasma filament. The timing controller 7 receives the trigger signal and starts the multi-channel data acquisition card 18, pulse laser 8 and camera 14 to work according to the set delay time, recording the acoustic-optical signal map and lateral shadow image at different positions when there is no cloud droplet influence.

[0063] Step 203: Use a metal baffle to block the output port of the femtosecond laser 1, i.e. the laser emission port, or block the first light-passing hole 4, turn on the atomizer 20 and the air pump 24, and continuously fill the cavity of the main chamber 22 with mist-containing airflow until the entire cavity is filled and the mist is visibly uniform.

[0064] Step 204: Remove the metal baffle of the laser emission port or the first light-passing hole 4. According to the change in the position of the plasma filament, move the spine-type ultrasonic transducer array 15 to the position above the plasma filament. Record the acoustic-optic signal map and lateral shadow image at different positions of the plasma filament when there is cloud droplet influence, in the same manner as in step 202.

[0065] Step 205: The acoustic-optical signal images and lateral shadow images under the influence of clouds and fog are transmitted to the computer respectively. The deposition energy measurement method during the cloud and fog penetration process of femtosecond laser is used for processing, and finally the three-dimensional deposition energy distribution maps of plasma filaments under the influence of clouds and fog are obtained.

[0066] Repeat steps 201 to 205 to obtain multiple sets of data and compare the three-dimensional distribution differences of photofilament deposition energy under conditions of no clouds and fog.

[0067] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the appended claims.

Claims

1. A method for measuring the deposition energy during femtosecond laser penetration of clouds and fog, characterized in that, The method includes: Obtain the lateral shadow map of the plasma filament under orthogonal viewpoints and the acousto-optic signal map at different positions along the transmission direction of the plasma filament; Based on the lateral shadow map, the shape contour information of the plasma filament is obtained, and a lateral cross-sectional view is obtained; Based on the acousto-optic signal maps at different locations, the energy absorption distribution information of the plasma filament is calculated to obtain a transverse cross-sectional view; The lateral cross-sectional image and the transverse cross-sectional image are fused to obtain a three-dimensional deposition energy distribution map of plasma filaments.

2. The method for measuring deposition energy during femtosecond laser cloud and fog penetration according to claim 1, characterized in that, Based on the lateral shadow map, the shape contour information of the plasma filament is obtained using the shadow method, resulting in a lateral cross-sectional view. .

3. The method for measuring deposition energy during femtosecond laser cloud and fog penetration according to claim 1 or 2, characterized in that, Based on the acousto-optic signal maps at different locations, the energy absorption distribution information of the plasma filament is calculated using a back-projection algorithm to obtain a transverse cross-sectional view.

4. The method for measuring deposition energy during femtosecond laser cloud and fog penetration according to claim 3, characterized in that, The energy absorption distribution information of the plasma filament is calculated using a back-projection algorithm to obtain a transverse cross-sectional view, including: The acoustic-optic signal maps at different locations are reconstructed using a back-projection algorithm, and the energy distribution information of the plasma filament is calculated to obtain a two-dimensional initial sound pressure intensity distribution map of the plasma filament. Based on the pressure-energy relationship, the initial two-dimensional sound pressure intensity distribution map is converted into a two-dimensional optical filament cross-section energy absorption distribution, resulting in transverse cross-sectional diagrams at different locations. .

5. The method for measuring deposition energy during femtosecond laser penetration of clouds and fog according to claim 4, characterized in that, The expression for the back projection algorithm is: ； In the formula, for The reconstructed sound pressure level at the location. This represents the distance from the scan center point to the reconstructed pixel. Indicates the scan center point to the th The distance between transducers Indicates the back projection term. Represents the solid angle weighting factor. For the entire measurement surface Relative to its interior Solid angle of position reconstruction Transducer surface detection unit Compared to Solid angle of the location reconstruction point This indicates the speed of sound in an adiabatic environment.

6. The method for measuring deposition energy during femtosecond laser penetration of clouds and fog according to claim 5, characterized in that, The relationship between pressure and energy is expressed as follows: ； in, This represents the initial sound pressure intensity distribution. This represents the initial absorbed energy distribution. The initial absorbed energy distribution map Transform into Cartesian coordinate system .

7. The method for measuring deposition energy during femtosecond laser cloud and fog penetration according to claim 6, characterized in that, The lateral cross-sectional view and the transverse cross-sectional view are fused to obtain a three-dimensional plasma filament deposition energy distribution map, including: The lateral cross-sectional image and the transverse cross-sectional image are fused using an image fusion method to obtain a three-dimensional deposition energy distribution map of the plasma filament, including: According to the Cross-sectional view obtained from the acoustic-optical data detected by the transducer array ,Will Non-zero boundary values ​​as The outer boundary profile of the plasma filament cross-section at that location; According to the lateral section diagram The shape of the plasma filament is obtained along... Width information in direction and along Length information in the direction; Lateral section diagram In Sectional views and multiple transverse section views In The cross-sectional view uses a convolutional neural network model to extract features, mapping the view features within a set of viewpoints to a new feature to obtain the view features; The view features are fused using a feature point matching method or a multilayer perceptron method to obtain the three-dimensional deposition energy distribution feature data of the plasma filament. ; The three-dimensional deposition energy distribution characteristic data A view rendering was performed to obtain a three-dimensional deposition energy distribution map of the plasma filament.

8. A device for measuring the deposition energy during femtosecond laser penetration of clouds and fog, characterized in that, The device includes: Main hull; A cloud and fog generating component is disposed around the main body and connected to the main body via a channel. An acousto-optic signal acquisition component is installed inside and around the main cabin. It emits a femtosecond laser, focuses it inside the main cabin to form a plasma filament, and obtains the acousto-optic signal map of the plasma filament. A lateral shadowing acquisition component, positioned around the main cabin, acquires a lateral shadowing map of the plasma filament by emitting pulsed laser light.

9. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to claim 8, characterized in that, The main cabin is a hollow structure, and it is provided with a first light-transmitting hole, a second light-transmitting hole, a third light-transmitting hole and a fourth light-transmitting hole. The first light-transmitting aperture and the second light-transmitting aperture are arranged opposite to each other to allow the femtosecond laser to pass through; The third light-transmitting aperture is positioned opposite to the fourth light-transmitting aperture to allow the pulsed laser to pass through.

10. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to claim 9, characterized in that, The acoustic-optic signal acquisition component includes: A femtosecond laser is positioned around the main cabin body to generate femtosecond lasers; A first reflecting mirror is disposed in the optical path of the femtosecond laser to change the direction of the femtosecond laser so that it passes through the first through hole of the main body; A focusing lens is disposed between the first reflector and the main body, and is located in the optical path of the femtosecond laser; A beam collector is disposed near the second through-hole of the main body and located in the optical path of the femtosecond laser to intercept the femtosecond laser emitted from the second through-hole; The photoacoustic measurement unit is fixed inside the main cabin and is set parallel to the transmission direction of the femtosecond laser. It is used to collect the acoustic signals generated at different positions along the transmission direction of the plasma filament formed by the femtosecond laser inside the main cabin.

11. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to claim 10, characterized in that, The photoacoustic measurement unit includes a spine-type ultrasonic transducer array, a lifting rod, a top slide rail, and a multi-channel data acquisition card. A spine-type ultrasonic transducer array is disposed within the cavity of the main body and parallel to the transmission direction of the plasma filament, in order to acquire photoacoustic signals generated at different positions of the plasma filament. The lifting boom includes a first connecting rod and a second connecting rod. The spine-type ultrasonic transducer array is arranged on the first connecting rod. One end of the second connecting rod is vertically fixed to the first connecting rod, and the other end is connected to the top slide rail for adjusting the height of the spine-type ultrasonic transducer array. The top slide rail is fixed on the inner wall of the main cabin cavity along the transmission direction of the plasma filament, and is connected to the spine-type ultrasonic transducer array through a lifting rod, for adjusting the horizontal position of the spine-type ultrasonic transducer array. The multi-channel data acquisition card is electrically connected to the spine-type ultrasonic transducer array and is used to acquire the photoacoustic signal.

12. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to claim 11, characterized in that, The spine-type ultrasonic transducer array comprises several transducers arranged in an array. The transducers are arc-shaped, with several uniformly arranged ultrasonic transducer elements on their inner arc surface.

13. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to claim 9, characterized in that, The lateral shadow map acquisition component includes: A pulsed laser, positioned around the main cabin, is used to generate pulsed laser light. The second reflector is used to change the direction of the pulsed laser so that it passes through the third light-transmitting hole of the main body; A diffuser plate, disposed between the second reflector and the third light-transmitting hole, is used to scatter the pulsed laser beam, thereby uniformly irradiating the plasma interaction area; A filter is disposed near the fourth light-passing hole to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament; A neutral density filter is placed behind the optical filter to filter out the scattered light from the femtosecond laser and the fluorescence generated by the plasma filament. A camera, positioned behind the neutral density filter, is used to capture the lateral shadow image. The second reflector, the diffuser, the filter, the neutral density filter, and the camera are all located in the optical path of the pulsed laser.

14. The device for measuring the deposition energy during femtosecond laser cloud and fog penetration according to any one of claims 9 to 13, characterized in that, The device also includes a timing controller and a computer; The timing controller is electrically connected to the camera, pulsed laser, and femtosecond laser. It is used to receive the trigger signal emitted by the femtosecond laser and send it to the multi-channel data acquisition card, and start the multi-channel data acquisition card, the pulsed laser, and the camera to work after a set delay. The computer is located around the main cabin and is electrically connected to the femtosecond laser and the multi-channel data acquisition card. It is used to monitor and display the working status of the femtosecond laser and the pulsed laser, the coordination between different component units, the storage and analysis of data, and the timing controller to transmit and receive signals.

15. The device for measuring the deposition energy during femtosecond laser penetration of clouds and fog according to claim 8, characterized in that, The cloud and fog generating components include an atomizer and an air pump; The main body is provided with an air inlet and an air outlet. The atomizer is located on one side of the air inlet and is connected to the air inlet through a channel. The air pump is located on one side of the air outlet and is connected to the air outlet through a channel.

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