CN114689898A - Device and method for observing femtosecond laser filamentation impact cloud droplets - Google Patents
Device and method for observing femtosecond laser filamentation impact cloud droplets Download PDFInfo
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Abstract
The invention discloses a device and a method for observing femtosecond laser filamentation impact cloud droplets, wherein the device comprises an experimental cylinder, two ends of the experimental cylinder are respectively communicated with a bent pipe and are respectively connected with a mist making component and a water vapor condensation collecting component; an experiment area is arranged in the middle of the experiment tube, a first light guide pipe and a second light guide pipe which are positioned on the same straight line are arranged at two ends of the experiment area, a femtosecond laser generating assembly is arranged at one side of the experiment tube, and a light beam collecting assembly is arranged in the second light guide pipe; the experimental cylinder is provided with a double-pulse laser generating assembly at the upper end of an experimental area, a plurality of groups of image collectors for collecting image information are arranged below the experimental cylinder, and the image collectors are electrically connected with a computer; a system calibration plate is arranged between the first light pipe and the second light pipe in a sliding mode. The problem that high-dynamic and high-resolution measurement of femtosecond laser impact cloud mist is difficult to achieve in the prior art is solved, and effective experimental data are provided for revealing a mechanism of forming an optical transmission channel by femtosecond laser cleaning.
Description
Technical Field
The invention relates to the field of cross application of optical physics and atmospheric science, in particular to a device and a method for observing femtosecond laser filamentation impact cloud droplets.
Background
Femtosecond laser cloud layer Drilling (Drilling holes in clouds) is a brand new mode which is generated internationally in recent years and artificially influences local cloud environment, the femtosecond laser transmission filamentation effect is mainly utilized to reduce the optical thickness on a laser transmission path, and the femtosecond laser transmission filamentation effect has important potential application prospect in the aspects of guiding strong laser and microwave transmission, assisting optical communication and the like and draws wide attention.
Laser filamentation is the long-distance transmission of plasma channels formed when optical kerr self-focusing and plasma self-defocusing reach dynamic equilibrium due to the competition between the two. Studies have shown that thermal stress shock effects (also called "optomechanical" effects) due to the momentary energy deposition of the optical filament are the fundamental cause of the formation of the optical transmission channel. Under the action of thermal stress impact, gas molecules and cloud particles are transported, and are considered as key physical processes for forming a transmission channel. However, since the radial range of the plasma filament acting space is only hundreds of micrometers, there is still a great technical difficulty in accurately obtaining information such as size distribution, motion trajectory, and spatial distribution (including quantity, concentration, and velocity) of a particle field, and a report on a fine experimental measurement result is not yet found.
Disclosure of Invention
The invention aims to provide a device and a method for observing femtosecond laser filamentation impact cloud droplets, which aim to solve the problems in the prior art.
In order to achieve the purpose, the invention provides the following scheme:
the invention provides a device for observing femtosecond laser filamentation impact cloud droplets, which comprises an experimental cylinder, wherein two ends of the experimental cylinder are respectively communicated with a bent pipe and are respectively connected with a mist making component and a water vapor condensation collecting component; an experiment area is arranged in the middle of the experiment tube, a first light guide pipe and a second light guide pipe which are positioned on the same straight line are arranged at two ends of the experiment area, a femtosecond laser generating assembly is arranged at one side of the experiment tube, and a light beam collecting assembly is arranged in the second light guide pipe; the experimental cylinder is provided with a double-pulse laser generating assembly at the upper end of the experimental area, a plurality of groups of image collectors for collecting image information are arranged below the experimental cylinder, and the image collectors are electrically connected with a computer; a system calibration plate is arranged between the first light pipe and the second light pipe in a sliding mode.
Preferably, the femtosecond laser generating assembly comprises a femtosecond laser and a first beam shaping assembly, and the femtosecond laser beam generated by the femtosecond laser is emitted into the first light guide pipe through the first beam shaping assembly.
Preferably, the double-pulse laser generating assembly comprises a double-pulse laser, a light guide arm and a second beam shaping assembly, and pulse laser beams generated by the double-pulse laser are emitted into the experimental area through the light guide arm and the second beam shaping assembly.
Preferably, the mist generating assembly comprises an ultrasonic humidifier for forming mist droplets and a blower for driving the wet gas flow with the mist droplets to move, and the mist generating assembly is arranged on the same side of the femtosecond laser generating assembly.
Preferably, the image collector is a CCD camera, and at least three groups of CCD cameras are arranged; the double-pulse laser is electrically connected with a time synchronizer, the time synchronizer is electrically connected with the CCD cameras, all the CCD cameras are electrically connected with an image acquisition card, and the image acquisition card is electrically connected with a computer.
Preferably, the experiment cylinder is of a hollow cylindrical structure, the inside of the experiment cylinder is of a jacket structure and comprises double layers of organic glass and a foam heat-insulating layer arranged between the double layers of organic glass; the experimental cylinder is provided with a black anti-reflection coating on the side wall of the experimental area.
Preferably, the experiment tube is connected with a first light pipe, a first light through hole is formed in the joint of the experiment tube and the first light pipe, the experiment tube is connected with a second light pipe, a second light through hole is formed in the joint of the experiment tube and the second light pipe, and the first light through hole, the first light pipe, the second light pipe and the second light through hole 3 are arranged on the same straight line and are parallel to the central axis of the experiment area; the first beam shaping component comprises a dry group of reflecting mirrors and a focusing lens, the focusing lens is arranged in parallel with the first light through hole, and a plurality of groups of reflecting mirrors are arranged between the focusing lens and the femtosecond laser and reflect the femtosecond laser beam generated by the femtosecond laser to the focusing lens.
A method for observing femtosecond laser filamentation impact cloud droplets is based on the device for observing femtosecond laser filamentation impact cloud droplets, and comprises the following steps:
s1, starting a femtosecond laser generating assembly, forming a plasma light wire in an experimental area after a femtosecond laser beam generated by the femtosecond laser generating assembly passes through a first light guide pipe, receiving the plasma light wire in a second light guide pipe by a light beam collecting assembly, and preliminarily determining a wire forming position;
s2, blocking the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the spatial positions and the shooting visual angles of the plurality of image collectors by using a system calibration plate, and determining the mapping relation between the image coordinates and the physical spatial scale of the measuring object;
s3, starting a mist making assembly, and obtaining stable cloud and mist airflow in an experimental area;
s4, using the two-dimensional projection images obtained by all the image collector arrays, and reconstructing the spatial distribution of the three-dimensional particle field by using a multiplication algebraic reconstruction algorithm;
s5, obtaining a motion velocity vector of the tracer particle by utilizing a cross-correlation algorithm according to the particle displacement in the image obtained by two times of continuous exposure, and obtaining a particle velocity image;
s6, removing the femtosecond laser beam shielding in the S2, repeating the S4 and the S5, and obtaining a particle field three-dimensional space distribution and a particle velocity image under the influence of the femtosecond laser;
s7, comparing experimental results of the situation without the femtosecond laser action and the situation with the femtosecond laser action, obtaining the particle transport characteristics under the action of the femtosecond laser filamentation impact, and indirectly estimating physical quantities such as the femtosecond laser shock wave intensity, the air pressure gradient peak value and the like.
Preferably, in S4, reconstructing the spatial distribution of the three-dimensional particle field by using a multiplicative algebraic reconstruction algorithm includes the following steps:
s4.1, setting coordinates and dividing reconstruction grids according to the size of an actual detection space range by combining an image collector and space position distribution;
s4.2, acquiring a weight coefficient and a projection value under a corresponding sight line;
and S4.3, reconstructing a three-dimensional gray matrix of the particle field through a plurality of updating iterations.
Preferably, the cross-correlation algorithm in S5 is a fast fourier transform FFT correlation algorithm, which includes the following steps:
s5.1, calculating cross-correlation functions in two trial areas at corresponding positions of the distribution of the two frames of three-dimensional particles to obtain the average displacement of each particle in a small area;
s5.2, calculating according to the magnification factor and the exposure time interval to obtain the speed;
and S5.3, obtaining the motion velocity vector of the trace particle to obtain a particle velocity image.
The invention discloses the following technical effects: the femtosecond laser beam emitted by the femtosecond laser forms an optical fiber in a cloud and fog environment of a test area after being reflected and focused, cloud and fog particles are impacted, a double-pulse laser illuminates a flow field of an optical fiber action area, a high-speed CCD camera is used for acquiring a scattered light intensity signal of the particles, and supporting software carried in a computer reconstructs acquired two-dimensional images to obtain physical quantities such as displacement, movement speed and the like of the particles. The invention belongs to a non-contact cloud and mist particle field measurement method, which can realize high spatial-temporal resolution measurement of space particle distribution and particle speed in a femtosecond laser filamentation and cloud and mist droplet impact process and inversion of pressure field and temperature field changes caused by an optical filament impact effect, and provides effective experimental data for application research of forming an optical transmission channel by femtosecond laser cleaning, thereby revealing a relevant mechanism of influencing cloud and mist droplet behaviors by femtosecond laser filamentation. The problem that high dynamic and high resolution measurement of femtosecond laser impact cloud and mist in the prior art is difficult to achieve is solved, effective experimental data are provided for revealing a mechanism that an optical transmission channel is formed by femtosecond laser cleaning, non-contact measurement of a cloud and mist droplet transportation process under the action of the femtosecond laser is achieved by utilizing a chromatography PIV (particle image velocimetry) technology, the advantages of large measurement field of view and high measurement spatial resolution are achieved, and a research platform can be provided for experimental research of an interaction process of the femtosecond laser and the cloud and mist.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a schematic diagram of an arrangement of CCD cameras according to the present invention.
The device comprises a test tube 1, a fog making component 2, a water vapor condensation collecting component 3, an experimental area 4, a first light guide tube 5, a second light guide tube 6, a light beam collecting component 7, a computer 8, a system calibration plate 9, a femtosecond laser 10, a double-pulse laser 11, a light guide arm 12, a second light beam shaping component 13, a CCD (charge coupled device) camera 14, a time synchronizer 15, an image acquisition card 16, a first light through hole 17, a second light through hole 18, a reflector 19, a focusing lens 20 and a third light through hole 21.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Referring to fig. 1-2, the device for observing femtosecond laser filamentation impact cloud droplets comprises an experimental cylinder 1, wherein two ends of the experimental cylinder 1 are respectively communicated with a bent pipe and respectively connected with a mist making component 2 and a water vapor condensation collecting component 3; experiment area 4 has been seted up at the middle part of a laboratory glassware 1, and the both ends of experiment area 4 are provided with first light pipe 5 and second light pipe 6 that are in the collinear, and one side of a laboratory glassware 1 is provided with femto second laser and takes place the subassembly, and femto second laser takes place the subassembly and includes femto second laser instrument 10 and first beam shaping subassembly, and femto second laser beam that femto second laser instrument 10 produced jets into first light pipe 5 through first beam shaping subassembly. A light beam collecting component 7 is arranged in the second light pipe 6; the experimental cylinder 1 is provided with a double-pulse laser generating assembly at the upper end of an experimental area 4, a plurality of groups of image collectors for collecting image information are arranged below the experimental cylinder 1, and the image collectors are electrically connected with a computer 8; a system calibration plate 9 is arranged between the first light pipe 5 and the second light pipe 6 in a sliding mode, and the system calibration plate 9 is a three-dimensional calibration plate. The light beam collection assembly 7 is a photodiode and is mainly used for measuring the laser power of the femtosecond laser beam passing through the cloud.
The front part of an experimental area 4 of the experimental cylinder 1 is provided with a plurality of metal damping nets or inserting plates so as to obtain higher-quality cloud airflow; the rear part of the experiment area 4 of the experiment barrel 1 is also provided with a metal damping net or a plugboard, and the water vapor condensation collection component 3 condenses water mist to prevent the backflow of the cloud and mist airflow. According to the invention, through arranging the metal damping net or the inserting plate to obtain higher-quality cloud airflow, and adding the black anti-reflection coating, the error in the experimental process can be effectively reduced.
The experiment cylinder 1 is designed into a low-speed wind tunnel structure, the experiment cylinder 1 is of a hollow cylindrical structure, the inside of the experiment cylinder 1 is of a jacket structure and comprises double layers of organic glass and a foam heat-insulating layer arranged between the double layers of organic glass; the experiment tube 1 is provided with a black anti-reflection coating on the side wall of the experiment area 4, the first light guide pipe 5 and the second light guide pipe 6 are deeply arranged inside the experiment tube 1, and the tail ends of the first light guide pipe 5 and the second light guide pipe 6 are sealed by quartz glass.
The experimental cylinder 1 is provided with a first observation window and a second observation window at two sides of an experimental area 4, a third light passing hole 21 is arranged at the upper part, a plane reflector is arranged at the lower part, and the light passing holes are sealed by quartz glass; the double-pulse laser generating assembly comprises a double-pulse laser 11, a light guide arm 12 and a second beam shaping assembly 13, wherein pulse laser beams generated by the double-pulse laser 11 pass through the light guide arm 12 and the second beam shaping assembly 13 and penetrate through a third light through hole 21 to enter the experimental area 4. The wavelength of the double-pulse laser 11 is generally 532nm, and the double-pulse laser is mainly used for generating a three-dimensional light source, and illuminating droplet particles in a flow field after being incident from the third light passing hole 21. The light guide arm 12 is composed of a steering knuckle, a reflecting mirror, a focusing mirror, a closed light path and the like, and is mainly used for guiding the transmission of double-pulse laser. The second beam shaping component 13 includes a powell prism and a triple prism, which are located at the exit of the light guide arm 12 and are respectively used for irradiating the vertical and horizontal beam expansion of the laser to obtain approximately uniform light intensity.
The fog-making assembly 2 comprises an ultrasonic humidifier for forming fog drops and a blower for driving wet air flow with the fog drops to move, the fog-making assembly 2 is arranged on the same side of the femtosecond laser generation assembly, the fog drops are used as tracer particles, and the concentration can be adjusted by changing the frequency of the humidifier. The invention can uniformly diffuse the water mist airflow generated by the humidifier into the cloud mist generating device through an external connection mode and ventilation equipment, and can conveniently realize the control of the internal water mist quantity, the particle concentration, the particle size and the like. The external humidifier can be replaced by a snow maker or a large-scale external cloud and fog chamber, and the particle phase state in the cloud and fog airflow can be controlled in a single or combined mode, so that various forms of clouds (fog) such as water cloud (fog), mixed cloud (fog) and ice phase cloud (fog) can be simulated, and the coverage range is wide and various.
The image collector is a CCD camera 14, at least three groups of CCD cameras 14 are arranged on the CCD camera 14, and trace particles in the flow field are shot and recorded from different visual angles; the double-pulse laser 11 is electrically connected with a time synchronizer 15, the time synchronizer 15 is electrically connected with the CCD cameras 14, all the CCD cameras 14 are electrically connected with an image acquisition card 16, and the image acquisition card 16 is electrically connected with the computer 8. The time synchronizer 15 is configured to receive the pulse emission signal of the double-pulse laser 11 and trigger the CCD camera 14 to operate, so as to ensure that the shooting time period of the CCD camera 14 is completely synchronized with the time period of the double-pulse laser 11. The image acquisition card 16 and the computer 8 are used for image storage and image reconstruction. In actual work, two independent laser heads of the double-pulse laser are controlled by the time synchronizer to enable a first laser pulse to fall on the first exposure time of the camera and enable a second laser pulse to fall on the second exposure time of the camera; the frame-crossing time of the CCD camera 14 is as small as possible (the shooting frequency is as large as possible) to improve the shooting capture capability of the camera, and a telecentric lens can be used in practice to reduce the error of image shooting.
The system calibration board 9 is a three-dimensional calibration board, the system calibration board 9 is moved along the thickness direction of the experimental area 4 during calibration, and each CCD camera 14 records calibration patterns at different depth of field positions to obtain corresponding calibration mapping functions. In addition, the measurement capability of the chromatography system can be checked by selecting tracer particles, the diameter of the selected tracer particles should be as close to the size of the cloud particle as possible, and the tracer particles with better light scattering property, such as the tracer particles made of dioctyl sebacate, polystyrene and the like, are generally selected.
The chromatography PIV is mainly characterized in that a three-dimensional space particle field is dispersed into a plurality of two-dimensional planes, and then trace particles in the flow field are shot and recorded by a plurality of (usually more than three) CCD cameras at different viewing angles to obtain a two-dimensional projection image, so that the two-dimensional projection image is simplified into a linear array. The arrangement of the plurality of cameras needs to be arranged according to the scheimpfug principle, the imaging plane of each camera corresponding to the target plane in the illuminated particle field. The position and the visual angle of the camera are calibrated in advance through a three-dimensional system calibration board. Fig. 2 is a schematic diagram showing 4 CCD cameras arranged by means of a cross. In addition, the numerical aperture of the objective lens can be increased in order to ensure that the depth of field matches the thickness of the illumination volume.
According to the further optimized scheme, the experiment tube 1 is connected with the first light pipe 5, the first light through hole 17 is formed in the joint of the experiment tube 1 and the first light pipe 5, the experiment tube 1 is connected with the second light pipe 6, the second light through hole 18 is formed in the joint of the experiment tube 1 and the second light pipe 6, and the first light through hole 17, the first light pipe 5, the second light pipe 6 and the second light through hole 183 are arranged on the same straight line and are parallel to the central axis of the experiment area 4; the first beam shaping assembly includes, for example, a dry group mirror 19 and one focusing lens 20, the focusing lens 20 being arranged in parallel with the first light passing hole 17, and several groups of mirrors 19 being disposed between the focusing lens 20 and the femtosecond laser 10 and reflecting the femtosecond laser beam generated by the femtosecond laser 10 onto the focusing lens 20.
A method for observing femtosecond laser filamentation impact cloud droplets, which is based on the device for observing femtosecond laser filamentation impact cloud droplets in any one of claims 1 to 7, and comprises the following steps:
s1, starting a femtosecond laser generating assembly, forming a plasma light wire in an experimental area 4 after a femtosecond laser beam generated by the femtosecond laser generating assembly passes through a first light guide pipe 5, receiving the plasma light wire by a light beam collecting assembly 7 in a second light guide pipe 6, and primarily determining a wire forming position.
S2, blocking the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the spatial positions and the shooting visual angles of the plurality of image collectors by using a system calibration plate 9, and determining the mapping relation between the image coordinates and the physical spatial scale of the measuring object.
S3, the fog making assembly 2 is started, and the experimental area 4 obtains stable cloud airflow.
S4, reconstructing the spatial distribution of the three-dimensional particle field by using the two-dimensional projection images obtained by all the image collector arrays and utilizing a multiplicative algebraic reconstruction algorithm; the method comprises the following steps:
s4.1, setting coordinates and dividing reconstruction grids according to the size of an actual detection space range by combining an image collector and space position distribution;
s4.2, acquiring a weight coefficient and a projection value under a corresponding sight line;
and S4.3, reconstructing a three-dimensional gray matrix of the particle field through a plurality of updating iterations.
S5, obtaining a motion velocity vector of the tracer particle by utilizing a cross-correlation algorithm according to the particle displacement in the image obtained by two times of continuous exposure, and obtaining a particle velocity image; the cross-correlation algorithm in the S5 is a fast fourier transform FFT correlation algorithm, and includes the following steps:
s5.1, calculating cross-correlation functions in two trial areas at corresponding positions of the distribution of the two frames of three-dimensional particles to obtain the average displacement of each particle in a small area;
s5.2, calculating according to the magnification factor and the exposure time interval to obtain the speed;
and S5.3, obtaining the motion velocity vector of the trace particle to obtain a particle velocity image.
S6, removing the femtosecond laser beam shielding in the S2, repeating the S4 and the S5, and obtaining a particle field three-dimensional space distribution and a particle velocity image under the influence of the femtosecond laser.
S7, comparing experimental results of the situation without the femtosecond laser action and the situation with the femtosecond laser action, obtaining the particle transport characteristics under the action of the femtosecond laser filamentation impact, and indirectly estimating physical quantities such as the femtosecond laser shock wave intensity, the air pressure gradient peak value and the like.
In the description of the present invention, it is to be understood that the terms "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, are merely for convenience of description of the present invention, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.
Claims (10)
1. The utility model provides an observation femto second laser filamentation strikes device of cloud droplet which characterized in that: the device comprises an experimental cylinder (1), wherein two ends of the experimental cylinder (1) are respectively communicated with a bent pipe and are respectively connected with a mist making assembly (2) and a water vapor condensation collection assembly (3); an experiment area (4) is arranged in the middle of the experiment tube (1), a first light guide tube (5) and a second light guide tube (6) which are positioned on the same straight line are arranged at two ends of the experiment area (4), a femtosecond laser generating assembly is arranged at one side of the experiment tube (1), and a light beam collecting assembly (7) is arranged in the second light guide tube (6); the experimental tube (1) is provided with a double-pulse laser generating assembly at the upper end of the experimental area (4), a plurality of groups of image collectors for collecting image information are arranged below the experimental tube (1), and the image collectors are electrically connected with a computer (8); a system calibration plate (9) is arranged between the first light guide pipe (5) and the second light guide pipe (6) in a sliding mode.
2. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 1, wherein: the femtosecond laser generating assembly comprises a femtosecond laser (10) and a first beam shaping assembly, and the femtosecond laser beam generated by the femtosecond laser (10) is injected into the first light guide pipe (5) through the first beam shaping assembly.
3. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 1, wherein: the double-pulse laser generation assembly comprises a double-pulse laser (11), a light guide arm (12) and a second beam shaping assembly (13), and pulse laser beams generated by the double-pulse laser (11) are injected into the experimental area (4) through the light guide arm (12) and the second beam shaping assembly (13).
4. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 1, wherein: the fog-making assembly (2) comprises an ultrasonic humidifier for forming fog drops and a blower for driving wet airflow with the fog drops to move, and the fog-making assembly (2) is arranged on the same side of the femtosecond laser generation assembly.
5. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 3, wherein: the image collector is a CCD camera (14), and at least three groups of CCD cameras (14) are arranged; the double-pulse laser (11) is electrically connected with a time synchronizer (15), the time synchronizer (15) is electrically connected with the CCD cameras (14), all the CCD cameras (14) are electrically connected with an image acquisition card (16), and the image acquisition card (16) is electrically connected with the computer (8).
6. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 1, wherein: the experimental cylinder (1) is of a hollow cylindrical structure, the interior of the experimental cylinder (1) is of a jacket structure and comprises double layers of organic glass and a foam heat-insulating layer arranged between the double layers of organic glass; the experimental cylinder (1) is provided with a black anti-reflection coating on the side wall of the experimental area (4).
7. The device for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 2, wherein: the experimental cylinder (1) is connected with the first light pipe (5), a first light through hole (17) is formed in the joint of the experimental cylinder (1) and the first light pipe, the experimental cylinder (1) is connected with the second light pipe (6), a second light through hole (18) is formed in the joint of the experimental cylinder (1) and the second light pipe, and the first light through hole (17), the first light pipe (5), the second light pipe (6) and the second light through hole (18) are arranged on the same straight line and are parallel to the central axis of the experimental area (4); the first beam shaping component comprises, for example, a dry group of mirrors (19) and a focusing lens (20), the focusing lens (20) is arranged in parallel with the first light through hole (17), and a plurality of groups of mirrors (19) are arranged between the focusing lens (20) and the femtosecond laser (10) and reflect the femtosecond laser beam generated by the femtosecond laser (10) to the focusing lens (20).
8. A method for observing femtosecond laser filamentation impact cloud droplets, which is based on the device for observing femtosecond laser filamentation impact cloud droplets as claimed in any one of claims 1 to 7, and is characterized in that: the method comprises the following steps:
s1, starting a femtosecond laser generation assembly, enabling a femtosecond laser beam generated by the femtosecond laser generation assembly to pass through a first light guide pipe (5) and then form a plasma optical filament in an experimental area (4), receiving the plasma optical filament in a second light guide pipe (6) by a light beam collection assembly (7), and preliminarily determining a filament forming position;
s2, blocking the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the spatial positions and the shooting visual angles of the plurality of image collectors by using a system calibration plate (9), and determining the mapping relation between the image coordinates and the physical spatial scale of the measuring object;
s3, starting the fog-making assembly (2), and obtaining stable cloud airflow in the experimental area (4);
s4, reconstructing the spatial distribution of the three-dimensional particle field by using the two-dimensional projection images obtained by all the image collector arrays and utilizing a multiplicative algebraic reconstruction algorithm;
s5, obtaining a motion velocity vector of the tracer particle by utilizing a cross-correlation algorithm according to the particle displacement in the image obtained by two times of continuous exposure, and obtaining a particle velocity image;
s6, removing the femtosecond laser beam shielding in the S2, and repeating the S4 and the S5 to obtain a particle field three-dimensional space distribution and a particle velocity image under the influence of the femtosecond laser;
s7, comparing the experimental results without the action of the femtosecond laser with the experimental results with the action of the femtosecond laser, obtaining the particle transport characteristics under the action of the filamentation impact of the femtosecond laser, and indirectly estimating the physical quantities such as the shock wave intensity of the femtosecond laser, the pressure gradient peak value and the like.
9. The method for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 8, wherein the method comprises the following steps: in S4, reconstructing the spatial distribution of the three-dimensional particle field by using a multiplicative algebraic reconstruction algorithm, including the steps of:
s4.1, setting coordinates and dividing reconstruction grids according to the size of an actual detection space range by combining an image collector and space position distribution;
s4.2, acquiring a weight coefficient and a projection value under a corresponding sight line;
and S4.3, reconstructing a three-dimensional gray matrix of the particle field through a plurality of updating iterations.
10. The method for observing femtosecond laser filamentation impact cloud droplets as claimed in claim 8, wherein the method comprises the following steps: the cross-correlation algorithm in the S5 is a fast fourier transform FFT correlation algorithm, and includes the following steps:
s5.1, calculating cross-correlation functions in two trial areas at corresponding positions of the distribution of the two frames of three-dimensional particles to obtain the average displacement of each particle in a small area;
s5.2, calculating according to the magnification factor and the exposure time interval to obtain the speed;
and S5.3, obtaining the motion velocity vector of the trace particle to obtain a particle velocity image.
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