Investigation On Obtaining A Hundreds Ps Pulse And Suppressing Its Tail Modulations Based On SBS Pulse Compression

As an important way to get high-intensity short pulse, Stimulated BrillouinScattering (SBS) pulse compression has great potential applications in laser inertialconfinement fusion, for its characters of simple-composition and self-pumping etc. Theobjective of the paper is finding the way to get hundreds-picoseconds short pulse andsuppressing its tail modulations based on SBS pulse compression, which can provideavailable seed laser pulse for the research of shock-ignition in laser inertial confinementfusion, as well as the short pulse need in the research of strong field physical, such ashigh-power protons radiation effects etc.Firstly, the physical process of SBS is analyzed phenomenologically, and the noiseorigin model of the SBS is deduced, based on the interactional equation set of pumping,Stokes and sonic wave fields. Then the mechanism of SBS pulse compression isanalyzed, the requirements to acquire the narrowest pulse was studied, the reasons forthe generation of tail modulations in the SBS pulse compression, in this part, theconcept of Stokes wave form dependence on pump effective pulse width was proposed,additionally the variation rules of the effective pulse width with the energy is studiedexperimentally and theoretically, which established the foundation for the research ofcutting the pumping effective pulse presented in the paper.Secondly, the influence on SBS pulse compression and tail modulation of pumplight parameters, structural parameters, and medium parameters is studied numerically.With the concept of effective energy reflection the variation rules of the tail modulationsand the cause is analyzed, from the view of the variation of the pumping effective pulsewidth with the parameters, the way to realize the tail modulation pulse with/under thehigh-pumping-energy by optimize the parameters is discussed.Finally, unilateral cut pump and bilateral cut pump to suppressing the tailmodulation of the hundreds picosecond pulse. The unilateral cut pump is the way ofusing short lens to cmpress the pulse and make the front of the pump light steep, thusslow the variation of the pump light effective interactive length with the energy, thencmpress the cutting pump with the long lens. The experiments demonstrate that with theprocess of unilateral cut pump, compared to the one without the process, has thenarrower pulse width of56ps, and the higher effective energy reflectivity, as much as50%. But there is a disadvantage of the method that an optical breakdown occurs whenthe energy getting higher. To make up this disadvantage a bilateral cut pump way isproposed, of which the basic idea is to increase the generation threshold of the Stokespulse under high pumping energy, thus shorten the effective pulse width of the pumplight, which is achieved with an attenuator set between the amplifier in experiment. With the increasing of the pumping energy, the effective energy reflectivity of theStokes pulse decrease all the time, which is only14.95%, while51%with the adoptionof a50%attenuator, and the tail modulation well suppressed, the Stokes pulse widthcompressed further, finally a output of284ps with little tail modulation, when theenergy is700mJ.