Experimental Study On Laser Propagation Characteristics In Local Atmospheric Turbulence Disturbed By Coherent Acoustic Waves

Laser technology has very important application value and prospects in fields such as communication,detection,ranging,and national defense.However,due to the presence of atmospheric turbulence,laser propagation in atmospheric turbulence can generate phenomena such as intensity fluctuation,beam drift,and beam expansion,which seriously restricts the development of laser technology.Acoustic wave is a kind of mechanical wave,which will change the internal structure and motion state of atmospheric turbulence in the process of propagation.Based on the characteristics of acoustic waves and the problems faced by laser technology in application,this thesis proposes to use sound waves to influence the internal structure and motion state of atmospheric turbulence,thereby affecting the transmission characteristics of laser in atmospheric turbulence.The influence of changes in acoustic wave parameters on the transmission characteristics of laser in atmospheric turbulence is studied,providing a new method for suppressing atmospheric turbulence effects.The main work of this thesis includes:1.Designed a local atmospheric turbulence simulation device and a coherent sound wave generation device,and conducted laser transmission experiments under the disturbance of coherent acoustic waves in a local atmospheric turbulence environment.Respectively adopt 4×4,3×3,2×2 planar array sound sources and circular array sound sources,studied the effects of changes in sound source array position,sound frequency,and sound power on intensity fluctuation,beam drift,and beam expansion during laser propagation in atmospheric turbulence under three different simulated atmospheric turbulence intensities.By collecting a large amount of experimental data,the scintillation index,beam drift nuctuation variance,and beam diameter were calculated to quantitatively describe the influence of coherent acoustic wave disturbed local atmospheric turbulence on laser transmission characteristics.2.The sound field distribution of coherent Sound waves generated by 4×4,3×3,2×2 planar array sound sources and circular array sound sources in the local atmospheric turbulence simulation device was simulated using COMSOL simulation software.We studied the effects of different positions,structures,and frequencies of sound source arrays on the distribution characteristics of coherent acoustic waves within a local atmospheric turbulence simulation device.3.Conducted laser propagation experiments under real atmospheric turbulence environment with acoustic disturbance.By using a single high-power sound source and changing the frequency and power of sound waves,the effects of sound wave disturbance on light intensity scintillation,beam drift,and beam expansion in a real atmospheric turbulent environment were studied.Collect sufficient experimental data,calculate the scintillation index,beam drift fluctuation variance,and beam diameter,and quantitatively describe the impact of acoustic wave disturbance on the laser transmission characteristics of real atmospheric turbulence.The result shows:Under the simulated atmospheric turbulence environment in the laboratory,coherent acoustic waves propagate in atmospheric turbulence,changing the internal structure and motion state of atmospheric turbulence,affecting laser transmission characteristics,and leading to the phenomenon of enhancing and suppressing atmospheric turbulence effects;The variance of beam drift fluctuation,scintillation index,and beam diameter exhibit certain regular changes with the variation of sound power,while there is no regular change with the variation of sound frequency;The placement position of the sound source array has little effect on the laser transmission characteristics.Different sound source array structures generate coherent acoustic waves to disturb local atmospheric turbulence,which has different effects on the laser transmission characteristics;Compared to 4×4,3×3 and 2×2 planar array sound sources,the circular array generates coherent acoustic waves to disturb atmospheric turbulence,which has a good impact on laser transmission characteristics;With the increase of the intensity of simulated atmospheric turbulence in the laboratory,the coherent acoustic waves generated by 4×4 planar array sound sources and circular array sound sources disturb the local atmospheric turbulence,and the effect on the laser transmission characteristics becomes worse.The coherent acoustic waves generated by planar array sound sources and circular array sound sources show a regular distribution of strong and weak fringes in the local atmospheric turbulence simulation device,different sound source array structure will lead to different spatial distribution of sound field;The higher the frequency of the acoustic wave,the smaller the distance between the strong and weak fringes;The greater the number of sound sources,the greater the sound field energy in the local atmospheric turbulence simulation device;In a real atmospheric turbulence environment,acoustic waves disturbed atmospheric turbulence,which will affect the transmission characteristics of laser in atmospheric turbulence.