Study On Influence Of Atmospheric Inhomogeneous Medium On Propagation Characteristics Of Femtosecond Pulse Laser

When femtosecond laser pulse is propagated in the atmosphere,the light focusing to high energy plasma channel due to the interaction between linear and nonlinear effects,causing the ‘filamentation'.Previous research has shown that the filaments of femtosecond laser have rich application potential in atmosphere like generating water condensate,triggering discharge and remote sensing of long distance.However,above potential applications often require long-distance propagated in cloud and rain environments,they will be disturbed by the atmospheric inhomogeneous medium,which will not only affect the stability of laser energy,but also affect the filamentation and inhibit the formation of filament.Among many impact factor,aerosol,cloud,fog,rainfall and turbulence are the most important factors affecting the evolution of filamentation of femtosecond laser pulse.This paper focuses on the influence of the above factors on the propagation characteristics of femtosecond laser,especially on the length,life and stability of filaments.In this paper,the effects of different types of cloud,fog,rainfall and aerosol on the propagation characteristics of femtosecond filaments were studied;the scattering effect of spherical and non-spherical aerosol on filaments was compared;the process of femtosecond filamentation under the influence of turbulence and particle scattering is investigated.The result shows that the laser of cirrus has the highest intensity and the longest filaments because of the weakest scattering,while the cumulus and stratocumulus have the strongest scattering,which cause the number of filaments is the least.The stratiform rainfall and convective rainfall with strong scattering have the shortest filamentation,while for mixed rainfall with the weakest scattering,the filamentation has the longest length.Among them,the light rain of mixed rainfall has the least influence on the beam,causing the highest energy and the largest number of filaments,while the scattering attenuation generated by medium rain and heavy rain is the strongest,and the filaments evolve into a cell structure with low energy value,with the shortest propagation distance.In the stratospheric aerosol,the main filament is wider and has the longest propagation distance,while the continental aerosol and maritime aerosol have stronger scattering and smaller filament radius.By comparing the scattering effects of non-spherical aerosol and spherical aerosol,it is found that the energy distribution in the non-spherical aerosol is more uniform,the light field information is more comprehensive,and a complete light filament structure is evolved.Except for the aerosol environment,the attenuation of other scattering environments is stronger than the turbulence disturbance,but the turbulence influence is still stronger than the particle scattering at the initial stage of propagation,so the onset of the filamentation in the turbulence is significantly lower than that in the scattering environment.In the mixture of turbulent and scattered particles,the evolution of filaments is more intense,and the propagation distance of filaments is shorter,especially in the mixture of stratocumulus and rainfall,the main filament dissipate and are replaced by small sub-filaments.These studies have laid a theoretical foundation for the further development of the transmission experiment and application of femtosecond laser in complex atmosphere...