CN114689898B - Device and method for observing femtosecond laser wire-forming impact cloud droplet - Google Patents
Device and method for observing femtosecond laser wire-forming impact cloud droplet Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/18—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance
- G01P5/20—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance using particles entrained by a fluid stream
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- G—PHYSICS
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- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
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- G01P5/18—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance
- G01P5/22—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the time taken to traverse a fixed distance using auto-correlation or cross-correlation detection means
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- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The invention discloses a device and a method for observing the impact of femtosecond laser filament forming on cloud fog drops, wherein the device comprises an experiment barrel, and two ends of the experiment barrel are respectively communicated with a bending pipe and are respectively connected with a fog making assembly and a water vapor condensation collection assembly; an experiment area is arranged in the middle of the experiment barrel, a first light pipe and a second light pipe which are positioned on the same straight line are arranged at two ends of the experiment area, a femtosecond laser generating component is arranged at one side of the experiment barrel, and a light beam collecting component is arranged in the second light pipe; the experimental barrel 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 barrel, and the image collectors are electrically connected with a computer; a system calibration plate is slidably arranged between the first light pipe and the second light pipe. The method solves the problem that the high-dynamic and high-resolution measurement of the femtosecond laser impact cloud is difficult to realize in the prior art, and provides effective experimental data for revealing the mechanism of forming an optical transmission channel by the femtosecond laser cleaning.
Description
Technical Field
The invention relates to the field of optical physics and atmospheric science cross application, in particular to a device and a method for observing femtosecond laser filament impact cloud droplets.
Background
The femtosecond laser cloud layer drilling (Drilling holes in clouds) is a brand new mode which is only internationally available in recent years and affects local cloud environment, the optical thickness on a laser transmission path is reduced mainly by utilizing the femtosecond laser transmission filamentation effect, and the method has important potential application prospects in the aspects of guiding strong laser, microwave transmission, assisting optical communication and the like, and draws wide attention.
Laser filament formation is a long-distance transmission plasma channel formed when optical kerr self-focusing and plasma self-defocusing are in dynamic balance due to competition. Studies have shown that thermal stress shock effects (also known as "optomechanical" effects) due to instantaneous energy deposition of the optical filaments are the root cause of the formation of optical transmission channels. Under the impact of thermal stress, gas molecules and cloud particles are transported, and are considered to be a key physical process for forming a transmission channel. However, as the radial range of the action space of the plasma optical fiber is only hundreds of micrometers, the information such as the size distribution, the motion track, the spatial distribution (including the quantity, the concentration, the speed and the like) of the particle field still has great technical difficulty at present, and no detailed experimental measurement result is reported.
Disclosure of Invention
The invention aims to provide a device and a method for observing the impact of femto-second laser filament forming on cloud droplets, so as to solve the problems in the prior art.
In order to achieve the above object, the present invention provides the following solutions:
the invention provides a device for observing the impact of femtosecond laser wire forming on cloud fog drops, which comprises an experiment barrel, wherein two ends of the experiment barrel are respectively communicated with a bending pipe and are respectively connected with a fog making assembly and a water vapor condensation collection assembly; an experiment area is arranged in the middle of the experiment barrel, a first light pipe and a second light 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 on one side of the experiment barrel, and a light beam collecting assembly is arranged in the second light pipe; the experimental barrel 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 barrel, and the image collectors are electrically connected with a computer; and a system calibration plate is slidably arranged between the first light pipe and the second light pipe.
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 injected into the first light guide tube through the first beam shaping assembly.
Preferably, the double-pulse laser generating component comprises a double-pulse laser, a light guide arm and a second beam shaping component, and the pulse laser beam generated by the double-pulse laser is injected into the experimental area through the light guide arm and the second beam shaping component.
Preferably, the mist generating assembly comprises an ultrasonic humidifier for forming mist droplets and a blower for driving the movement of the wet gas flow with mist droplets, and is arranged on the same side of the femtosecond laser generating assembly.
Preferably, the image collector is a CCD camera, and the CCD camera is provided with at least three groups; 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 image acquisition cards, and the image acquisition cards are electrically connected with the computer.
Preferably, the experimental barrel is of a hollow cylindrical structure, the inside of the experimental barrel 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 barrel is provided with a black anti-reflection coating on the side wall of the experimental area.
Preferably, the experimental barrel is connected with the first light pipe, a first light through hole is formed in the joint of the experimental barrel and the first light pipe, the experimental barrel is connected with the second light pipe, a second light through hole is formed in the joint of the experimental barrel 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 experimental area; the first beam shaping assembly comprises a plurality of groups of reflectors and a focusing lens, the focusing lens is arranged in parallel with the first light through hole, and the plurality of groups of reflectors 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 the impact of femtosecond laser wire forming on cloud fog drops is based on the device for observing the impact of femtosecond laser wire forming on cloud fog drops, 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 pipe, and then receiving the plasma light wire in a second light pipe by a beam collecting assembly to preliminarily determine a wire forming position;
s2, shielding the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the space positions of a plurality of image collectors and the photographed visual angles by utilizing a system calibration plate, and determining the mapping relation between the image coordinates and the physical space scale of the measuring body;
s3, starting a fog making assembly, and obtaining stable cloud fog airflow in an experimental area;
s4, reconstructing the spatial distribution of the three-dimensional particle field by using two-dimensional projection images obtained by all the image collector arrays and utilizing a multiplication algebraic reconstruction algorithm;
s5, obtaining a motion velocity vector of the tracer particle by using a cross-correlation algorithm according to the particle displacement in the images obtained by the two continuous exposures, and obtaining a particle velocity image;
s6, removing the shielding of the femtosecond laser beam in the S2, and repeating the S4 and the S5 to obtain three-dimensional spatial distribution of a particle field and a particle velocity image under the influence of the femtosecond laser;
s7, comparing experimental results without the action of the femtosecond laser and under the action of the femtosecond laser to obtain particle transport characteristics under the action of the femtosecond laser wire-forming impact, and indirectly estimating the intensity of the femtosecond laser shock wave and the peak value of the air pressure gradient.
Preferably, in S4, the reconstruction of the spatial distribution of the three-dimensional particle field by using a multiplicative algebraic reconstruction algorithm comprises the following steps:
s4.1, according to the size of the actual detection space range, combining an image collector and space position distribution, setting coordinates and reconstructing grid division;
s4.2, obtaining weight coefficients and projection values under corresponding vision lines;
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, comprising the steps of:
s5.1, calculating cross-correlation functions in two test areas of corresponding positions of two frames of three-dimensional particle distribution to obtain average displacement of each particle in a small area;
s5.2, calculating according to the magnification and the exposure time interval to obtain the speed;
s5.3, obtaining a motion velocity vector of the tracer particle, and obtaining a particle velocity image.
The invention discloses the following technical effects: the invention relates to a method for preparing a laser device, which comprises the steps of reflecting and focusing a femtosecond laser beam emitted by a femtosecond laser, forming a light wire in a cloud and fog environment of a test area, generating impact action on cloud and fog particles, illuminating a flow field of an action area of the light wire by a double-pulse laser, acquiring a scattered light intensity signal of the particles by a high-speed CCD camera, reconstructing an acquired two-dimensional image by matched software carried in a computer, and obtaining physical quantities such as displacement, movement speed and the like of the particles. The invention belongs to a non-contact cloud and fog particle field measurement method, which can realize high space-time resolution measurement of space particle distribution and particle speed in the process of impacting cloud and fog drops by femtosecond laser wire forming, and inversion of pressure field and temperature field change caused by light wire impact, and provides effective experimental data for application research of an optical transmission channel formed by femtosecond laser cleaning, thereby revealing a relevant mechanism of influencing cloud and fog drop behaviors by the femtosecond laser wire forming. The method solves the problem that the high-dynamic and high-resolution measurement of the femto-second laser impact cloud is difficult to realize in the prior art, provides effective experimental data for revealing the mechanism of forming an optical transmission channel by femto-second laser cleaning, realizes non-contact measurement of the cloud and mist drop transportation process under the action of the femto-second laser by utilizing a chromatography PIV technology, has the advantages of large measurement field of view and high measurement spatial resolution, and can provide a research platform for experimental research of the interaction process of the femto-second 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 that are 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 other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of the structure of the device of the present invention;
fig. 2 is a schematic diagram of an arrangement of a CCD camera according to the present invention.
The device comprises a test barrel 1, a mist making component 2, a water vapor condensation collecting component 3, a test area 4, a first light pipe 5, a second light pipe 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 camera 14, a time synchronizer 15, an image acquisition card 16, a first light through hole 17, a second light through hole 18, a reflecting mirror 19, a focusing lens 20 and a third light through hole 21.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Referring to fig. 1-2, the device for observing the impact of femto-second laser filament forming on cloud droplets comprises an experiment barrel 1, wherein two ends of the experiment barrel 1 are respectively communicated with a bending pipe and are respectively connected with a mist making component 2 and a water vapor condensation collection component 3; the experimental zone 4 has been seted up at the middle part of experimental section of thick bamboo 1, and the both ends of experimental zone 4 are provided with first light pipe 5 and second light pipe 6 that are in on the same straight line, and one side of experimental section of thick bamboo 1 is provided with femtosecond laser generating component, and the femtosecond laser generating component includes femtosecond laser 10 and first beam shaping subassembly, and the femtosecond laser beam that femtosecond laser 10 produced is penetrated into first light pipe 5 through first beam shaping subassembly. A beam collecting component 7 is arranged in the second light pipe 6; the experimental barrel 1 is provided with a double-pulse laser generating component 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 barrel 1, and the image collectors are electrically connected with a computer 8; a system calibration plate 9 is slidably arranged between the first light pipe 5 and the second light pipe 6, and the system calibration plate 9 is a three-dimensional calibration plate. The beam collecting component 7 is a photodiode and is mainly used for measuring laser power of the femtosecond laser beam passing through the cloud.
The front part of an experiment area 4 of the experiment barrel 1 is provided with a plurality of metal damping nets or plugboards so as to obtain higher-quality cloud and mist 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 assembly 3 condenses the water mist so as to prevent the back flow of the water mist air flow. According to the invention, by arranging the metal damping net or the plugboard to obtain higher-quality cloud and mist airflow, adding the black anti-reflection coating and the like, errors in the experimental process can be effectively reduced.
The experimental barrel 1 is generally designed into a low-speed wind tunnel structure, the experimental barrel 1 is of a hollow cylindrical structure, the inside of the experimental barrel 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 barrel 1 is provided with a black anti-reflection coating on the side wall of the experimental zone 4, the first light pipe 5 and the second light pipe 6 penetrate into the experimental barrel 1, and the ends of the first light pipe 5 and the second light pipe 6 are sealed by quartz glass.
The experimental barrel 1 is provided with a first observation window and a second observation window at two sides of an experimental area 4, a third light through hole 21 is formed above the experimental barrel, a plane reflector is arranged below the experimental barrel, and the light through hole is sealed by quartz glass; the double-pulse laser generating component comprises a double-pulse laser 11, a light guide arm 12 and a second beam shaping component 13, and a pulse laser beam generated by the double-pulse laser 11 is emitted into the experimental zone 4 through the light guide arm 12 and the second beam shaping component 13 and penetrates through a third light-passing hole 21. The double pulse laser 11 has a wavelength of 532nm, and is mainly used for generating a stereoscopic light source, and illuminating fogdrop particles in a flow field after being injected from the third light-passing hole 21. The light guide arm 12 is composed of a knuckle, a reflecting mirror, a focusing mirror, a closed light path and the like, and is mainly used for guiding the transmission of the double-pulse laser. The second beam shaping component 13 includes a powell lens and a triangular prism, and is located at the exit of the light guide arm 12, and is used for respectively irradiating the vertical and horizontal expanded beams of laser light, so as to obtain approximately uniform light intensity.
The mist generating assembly 2 comprises an ultrasonic humidifier for forming mist droplets and a blower for driving the movement of the wet gas flow with the mist droplets, the mist generating assembly 2 being arranged on the same side of the femtosecond laser generating assembly, wherein the mist droplets are used as trace particles, and the concentration can be adjusted by changing the frequency of the humidifier. The invention evenly diffuses the water mist air flow 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 snowmaking machine or an external large cloud fog room, and the like, 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 clouds (fog), mixed clouds (fog) and ice Xiang Yun (fog) can be simulated, and the coverage range is wide and various.
The image collector is a CCD camera 14, the CCD camera 14 is provided with at least three groups, 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 CCD cameras 14, all 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 used for receiving the pulse emission signal of the double pulse laser 11 and triggering the CCD camera 14 to work 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 is used with the computer 8 for image storage and image reconstruction. In actual operation, the two independent laser heads of the double-pulse laser device, the time synchronizer controls the first laser pulse to fall on the first exposure time of the camera, and the 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 high as possible) to improve the shooting capturing capability of the camera, and a telecentric lens can be used in practical use to reduce errors generated by image shooting.
The system calibration plate 9 is a three-dimensional calibration plate, the system calibration plate 9 is moved along the thickness direction of the test 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 tracer particles can be selected to test the measurement capability of the chromatographic system, the diameter of the selected tracer particles is as close to the scale of cloud and fog particles as possible, and the tracer particles with good light scattering property, such as dioctyl sebacate, polystyrene and other materials, are generally selected.
The chromatography PIV mainly comprises the steps of dispersing a three-dimensional space particle field into a plurality of two-dimensional planes, and then shooting and recording trace particles in the flow field by utilizing a plurality of (usually more than three) CCD cameras at different visual angles to obtain a two-dimensional projection image, so that the three-dimensional space particle field is simplified into a linear array. The arrangement of the plurality of cameras needs to be arranged according to the Scheimpug 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 plate. Fig. 2 is a schematic diagram showing an arrangement of 4 CCD cameras by means of a cross. In addition, to ensure that the depth of field matches the thickness of the illuminated volume, the numerical aperture of the objective can also be increased.
In a further optimization scheme, the experimental barrel 1 is connected with the first light pipe 5, a first light-passing hole 17 is formed in the joint of the experimental barrel 1 and the first light pipe 5, the experimental barrel 1 is connected with the second light pipe 6, a second light-passing hole 18 is formed in the joint of the experimental barrel 1 and the experimental barrel, and the first light-passing hole 17, the first light pipe 5, the second light pipe 6 and the second light-passing hole 183 are arranged on the same straight line and are parallel to the central axis of the experimental area 4; the first beam shaping assembly comprises a plurality of sets of mirrors 19 and a focusing lens 20, the focusing lens 20 being arranged in parallel with the first light-passing hole 17, the plurality of sets of mirrors 19 being arranged 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 the impact of femtosecond laser wire-formed cloud droplets, which is based on the device for observing the impact of femtosecond laser wire-formed cloud droplets according to any one of claims 1-7, and comprises the following steps:
s1, starting a femtosecond laser generating assembly, enabling a femtosecond laser beam generated by the femtosecond laser generating assembly to pass through a first light pipe 5 to form a plasma light wire in an experiment area 4, and then receiving the plasma light wire in a second light pipe 6 by a beam collecting assembly 7 to preliminarily determine a wire forming position.
S2, shielding the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the space positions of a plurality of image collectors and the photographed visual angles by utilizing a system calibration plate 9, and determining the mapping relation between the image coordinates and the physical space scale of the measuring body.
S3, starting the fog making assembly 2, and obtaining stable cloud fog airflow in the experimental area 4.
S4, reconstructing the spatial distribution of the three-dimensional particle field by using two-dimensional projection images obtained by all the image collector arrays and utilizing a multiplication algebraic reconstruction algorithm; the method comprises the following steps:
s4.1, according to the size of the actual detection space range, combining an image collector and space position distribution, setting coordinates and reconstructing grid division;
s4.2, obtaining weight coefficients and projection values under corresponding vision lines;
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 using a cross-correlation algorithm according to the particle displacement in the images obtained by the two continuous exposures, and obtaining a particle velocity image; the cross-correlation algorithm in S5 is a fast Fourier transform FFT correlation algorithm, comprising the following steps:
s5.1, calculating cross-correlation functions in two test areas of corresponding positions of two frames of three-dimensional particle distribution to obtain average displacement of each particle in a small area;
s5.2, calculating according to the magnification and the exposure time interval to obtain the speed;
s5.3, obtaining a motion velocity vector of the tracer particle, and obtaining a particle velocity image.
S6, removing the shielding of the femtosecond laser beam in the S2, and repeating the S4 and the S5 to obtain the three-dimensional spatial distribution of the particle field and the particle velocity image under the influence of the femtosecond laser.
S7, comparing experimental results without the action of the femtosecond laser and under the action of the femtosecond laser to obtain particle transport characteristics under the action of the femtosecond laser wire-forming impact, and indirectly estimating the intensity of the femtosecond laser shock wave and the peak value of the air pressure gradient.
In the description of the present invention, it should be understood that the terms "longitudinal," "transverse," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present invention, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (10)
1. Device of observing femto second laser filamentation impact cloud droplet, its characterized in that: the device comprises an experiment barrel (1), wherein two ends of the experiment barrel (1) are respectively communicated with a bending pipe and are respectively connected with a fog making component (2) and a water vapor condensation collection component (3); an experiment area (4) is formed in the middle of the experiment barrel (1), a first light pipe (5) and a second light pipe (6) which are positioned on the same straight line are arranged at two ends of the experiment area (4), a femtosecond laser generation assembly is arranged on one side of the experiment barrel (1), and a light beam collection assembly (7) is arranged in the second light pipe (6); the experimental barrel (1) is provided with a double-pulse laser generating component 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 barrel (1), and the image collectors are electrically connected with a computer (8); a system calibration plate (9) is slidably arranged between the first light pipe (5) and the second light pipe (6).
2. The device for observing the impact of femto-second laser filamentation on cloud droplets according to claim 1, wherein: the femtosecond laser generating assembly comprises a femtosecond laser (10) and a first beam shaping assembly, wherein a femtosecond laser beam generated by the femtosecond laser (10) is injected into the first light guide tube (5) through the first beam shaping assembly.
3. The device for observing the impact of femto-second laser filamentation on cloud droplets according to claim 1, wherein: the double-pulse laser generating 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 the impact of femto-second laser filamentation on cloud droplets according to claim 1, wherein: the mist generating component (2) comprises an ultrasonic humidifier for forming mist drops and a blower for driving the movement of the wet gas flow with the mist drops, and the mist generating component (2) is arranged on the same side of the femtosecond laser generating component.
5. A device for observing the impact of femtosecond laser filamentation on cloud droplets as claimed in claim 3, wherein: the image collector is a CCD camera (14), and the CCD camera (14) is provided with at least three groups; the double-pulse laser device is characterized in that the double-pulse laser device (11) is electrically connected with a time synchronizer (15), the time synchronizer (15) is electrically connected with a CCD camera (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 a computer (8).
6. The device for observing the impact of femto-second laser filamentation on cloud droplets according to claim 1, wherein: the experimental barrel (1) is of a hollow cylindrical structure, the inside of the experimental barrel (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 barrel (1) is provided with a black anti-reflection coating on the side wall of the experimental area (4).
7. The device for observing the impact of femto-second laser filamentation on cloud droplets according to claim 2, wherein: the experimental barrel (1) is connected with the first light pipe (5), a first light through hole (17) is formed in the joint of the experimental barrel (1) and the first light pipe (5), the experimental barrel (1) is connected with the second light pipe (6), a second light through hole (18) is formed in the joint of the experimental barrel (1), 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 assembly comprises a plurality of groups of reflectors (19) and a focusing lens (20), the focusing lens (20) is arranged in parallel with the first light transmission hole (17), and the plurality of groups of reflectors (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 the impact of femtosecond laser wire-forming on cloud droplets, which is based on the device for observing the impact of femtosecond laser wire-forming on cloud droplets, and is characterized in that: the method comprises the following steps:
s1, starting a femtosecond laser generating assembly, enabling a femtosecond laser beam generated by the femtosecond laser generating assembly to pass through a first light pipe (5) and then form a plasma light wire in an experiment area (4), and then receiving the plasma light wire in a second light pipe (6) by a beam collecting assembly (7), and primarily determining a wire forming position;
s2, shielding the femtosecond laser beam, starting and adjusting the double-pulse laser generating assembly, calibrating the space positions of a plurality of image collectors and the photographed visual angles by utilizing a system calibration plate (9), and determining the mapping relation between the image coordinates and the physical space scale of the measuring body;
s3, starting the fog making assembly (2), and obtaining stable cloud and fog airflow in the experimental area (4);
s4, reconstructing the spatial distribution of the three-dimensional particle field by using two-dimensional projection images obtained by all the image collector arrays and utilizing a multiplication algebraic reconstruction algorithm;
s5, obtaining a motion velocity vector of the tracer particle by using a cross-correlation algorithm according to the particle displacement in the images obtained by the two continuous exposures, and obtaining a particle velocity image;
s6, removing the shielding of the femtosecond laser beam in the S2, and repeating the S4 and the S5 to obtain three-dimensional spatial distribution of a particle field and a particle velocity image under the influence of the femtosecond laser;
s7, comparing experimental results without the action of the femtosecond laser and under the action of the femtosecond laser to obtain particle transport characteristics under the action of the femtosecond laser wire-forming impact, and indirectly estimating the intensity of the femtosecond laser shock wave and the peak value of the air pressure gradient.
9. The method for observing the impact of femto-second laser filamentation on cloud droplets as claimed in claim 8, wherein the method comprises the following steps: s4, reconstructing the spatial distribution of the three-dimensional particle field by using a multiplication algebraic reconstruction algorithm, wherein the method comprises the following steps of:
s4.1, according to the size of the actual detection space range, combining an image collector and space position distribution, setting coordinates and reconstructing grid division;
s4.2, obtaining weight coefficients and projection values under corresponding vision lines;
s4.3, reconstructing a three-dimensional gray matrix of the particle field through a plurality of updating iterations.
10. The method for observing the impact of femto-second laser filamentation on cloud droplets as claimed in claim 8, wherein the method comprises the following steps: the cross-correlation algorithm in S5 is a fast Fourier transform FFT correlation algorithm, comprising the following steps:
s5.1, calculating cross-correlation functions in two test areas of corresponding positions of two frames of three-dimensional particle distribution to obtain average displacement of each particle in a small area;
s5.2, calculating according to the magnification and the exposure time interval to obtain the speed;
s5.3, obtaining a motion velocity vector of the tracer particle, and obtaining a particle velocity image.
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