Research On The Generation Of Downward Step Pulse Based On SBS

Stimulated Brillouin Scattering(SBS)pulse compression can be used to generate high-intensity ultrashort pulses,and has the characteristics of simple structure,phase conjugation,small frequency shift and high energy extraction efficiency.Therefore,it has attracted great attention in the ignition scheme research of inertial confinement fusion.Besides the characteristics of pulse compression,SBS also has the ability of waveform modulation,and can be used as pump light for other non-linear effects by means of the downward step pulses generated.The purpose of this paper is to study how to obtain the downward step pulses based on the waveform modulation ability of SBS.Firstly,this paper describes the current research situation of SBS pulse compression technology,and describes the changes of SBS pulse compression media and compression structure in detail,as well as the achievements of many researchers.It is pointed out that the current work on SBS mainly focuses on how to obtain high-energy ultra-short pulses and how to suppress the tail modulation phenomenon,but not on the waveform modulation ability of SBS.Secondly,based on the physical process and coupled wave equation of SBS,the establishment of Stokes light in SBS and the process of energy transfer from pump light to Stokes light are theoretically deduced,and the coupled wave equation is deduced discretely to obtain the numerical solution model.The reason of tail modulation in SBS pulse compression is explained by the concept of effective interaction distance.For the downward step pulse obtained by SBS shaping,several indexes describing its characteristics are proposed.Thirdly,according to the numerical solution model,the effects of pump parameters,optical parameters and medium parameters on the SBS pulse compression and tail modulation phenomena in a single cell structure are studied,and the parameters for obtaining an downward step pulse with a certain level of tail modulation phenomena are obtained.Finally,a single-cell SBS experimental device for obtaining the downward step pulse is built.Experiments are carried out under different optical parameters and medium parameters.The range of pump energy that can generate the downward step pulse in different medium is obtained,and the parameters of the downward step pulse under different parameters,such as rise-edge duration,the ratio of duration and intensity between step and full pulse,are compared.The scheme of obtaining downward step pulse is obtained.Using FC-40 as SBS medium,the downward step pulses with the ratio of duration between step and full pulse accounting for 38.75% and the ratio of intensity between step and full pulse accounting for 65.17% were obtained respectively at different pump energies.