Pulse Compression Based On Stimulated Brillouin Scattering And Laser Induced Breakdown

Nowadays Inertial Confinement Fusion?ICF?has become a critical solution to the energy crisis.As a new ignition scheme,the shock-ignition gets great attention recently.The key of this technology is generation of shock pulse with hundreds pulse duration.The pulse compression technology based on stimulated Brillouin scattering?SBS?is potential to generate hundreds-of-picoseconds pulses with high power as well as high energy for the characteristics of simplification of experimental scheme,phase conjugation and high load capacity,etc.On the other hand,with a high power and sharp leading edge,the output pulse generated by SBS is suitable for laser induced breakdown?LIB?shutter to further compression.Thus,in this paper,researches on sub-phonon lifetime SBS compression and two-stage compression by SBS and LIB have been carried out,hoping to make a contribution to the generation of short laser pulse.First of all,we retrospect the development on SBS pulse compression.We present the research status of SBS active medium,SBS compression scheme and the compression technique combinations with SBS.According to the analysis,the research emphasis of SBS is to achieve sub-phonton lifetime compression by SBS itself or combination with other compression technique.By contrasting the technique combination SBS with stimualted Raman scattering,optical gain switcing and LIB,we draw conclusion that LIB plasma shutter is an ideal option combination with SBS.Then,staring from the coupled wave equations describing SBS and using a scheme with an implicit finite differencing in time and a down-wind differencing in space,we established the numerical calculation model.The numerical calculation of output stokes duration after SBS compression show that subnanosecond pulses can be generated by SBS compression.Then the plasma density evolutive rate equations is presented.An analytical solution of the threshold parameters can be given,which demonstrated that hundreds of picoseconds pump pulses can decrease the threshold of LIB significantly.Next,the phenomenon of tail modulation and Stokes duration broadening in the process of SBS compression is analyst through experiment of conventional single SBS compressor.It has been presented that the phenomenon of Stokes duration broadening is caused by the forward generation-position of Stokes.In experiment,tail modulation and Stokes duration broadening are suppressed,to a certain extent,using compact two cell compression scheme and double compressor structure.Fundamentally,an interferometric scheme is used to fix the generation position of Stokes seed and effectively suppress the broadening.Moreover,the interferometric scheme shows a promotion for the performance of SBS compression to archieve sub-phonon lifetime compression.Furthermore,considering the influence of pump waveform,we studies the effects of pump waveform on SBS comrpession.Experiments have show that sub-phonon lifetime SBS compression can be realized by using triangular pulses and step pump pulses.The ratio of leading-edge of pump waveform to the medium phonon lifetime(?_B/t_risingtime)is identified experimentally as the key parameter in quasi-steady-state SBS compression.An interferometric SBS scheme is utilized for quasi-steady-state SBS compression with a step pulse pump.The feasibility of this approach is demonstrated experimentally and a compression output of 0.12?_B?near-compression-limited?is obtained.At last,a laser pulse temporal compression technique combining SBS and laser-induced breakdown is proposed in which the leading edge of the laser pulse is compressed using SBS and the low intensity tailing edge of the laser pulse is truncated by LIB.The feasibility of the proposed scheme is demonstrated by experiments in ultrapure water.Truncation of the leading edge via SBS enhances the performance of LIB significantly.The amplified optical power of the leading edge decreases the energy threshold of LIB,and a short pulse increases the energy conversion of the generated plasma.On the other hand,as discussed,LIB compression can be an effective complement to SBS compression for removing the long tail region of the Stokes pulse.To enhance the effect of LIB compression,?-Al₂O₃ micro nanoparticles and noble metal Au,Ag nanoparticles are doped at LIB medium,respectively.The particles enhance the stability of output effectively.