皮秒激光驱动下的背向受激布里渊散射的光谱结构

Spectral structures of backward stimulated Brillouin scattering driven by a picosecond laser

激光等离子体相互作用(LPI)是激光等离子体相关研究中的重要内容,皮秒激光的出现为在皮秒时间尺度内更加细致地研究LPI过程提供了可能.LPI相关的时间尺度通常是皮秒量级的,这一研究有望从更精细的角度来获得认识.依托神光-Ⅱ升级及皮秒激光装置,开展了皮秒激光驱动LPI的实验研究.实验给出了背向受激布里渊散射(SBS)的积分光谱,其中除了真正的背向SBS成分,还包含大量的皮秒激光和纳秒激光引入的干扰信号.纳秒激光引入的干扰信号可以消除,但皮秒激光引入的干扰信号无法从实验角度消除,这势必会影响到对背向SBS真正份额的估计.结果显示,在不同的实验条件下,背向SBS散射能量在总的记录信号中,占比可能还不到一半.这一结果有助于对先前相关实验数据的进一步理解和再认识.

Laser plasma interaction(LPI)is an important content in laser plasma related research,and it is one of the key issues related to the success or failure of inertial confinement fusion ignition,and has received extensive attention.In order to suppress the relevant LPI process as much as possible,the major laboratories around the world have developed a variety of beam smoothing methods through decades of research.However,the current understanding and suppression of LPI are still far from enough,and further in-depth studies are still needed.Generally,the research of LPI is based on nanosecond laser driving,and focuses mainly on the effects of the related LPI process caused by nanosecond lasers.However,the LPI processes,such as stimulated Brillouin scattering(SBS),stimulated Raman scattering(SRS),etc.,occur and develop on a time scale of picoseconds.The comprehensive effect can be studied only on a longer scale of nanosecond.For highly nonlinear LPI processes,the comprehensive effect may be difficult to reflect the real physical laws.The emergence of the picosecond laser has made it possible to study the LPI process in more detail and on a more appropriate time scale.The present research tries to gain an understanding of LPI from a more refined perspective.The experimental research of picosecond laser driving LPI is carried out on the Shenguang-Ⅱupgrade and picosecond laser facilities.First,a nanosecond laser is used to irradiate a target to generate a large-scale plasma,and a few nanoseconds later,the picosecond laser is injected as an interaction beam to drive the LPI scattering such as SBS and SRS.The spectral signal of backscatter light is measured experimentally by using the method of diffuse reflector.From the research results it is found that the backward signals of the band near the laser wavelength contain,in addition to the true backward SBS component,a large number of interference signals introduced by picosecond laser and nanosecond laser.The interference signal introduced by nanosecond laser can be eliminated by using specific measures,but the interference signal introduced by picosecond laser cannot be eliminated experimentally,which will affect the estimation of the true share of the backward SBS.The comprehensive results show that under different experimental conditions,the backward scatter energy of SBS may be less than half that of the total recorded signals.This result is helpful in further understanding and re-recognizing previous relevant experimental data.