Investigation On Generation And Waveform Fidelity Amplification Charcteristics Of Hundred Picoseconds Pulses Based On Stimulated Brillouin Scattering

As the core of shock ignition scheme which is for the purpose of driving inertial confinement fusion,hundred picosecond laser pulses with high power have been extensively concerned.In addition,hundred picosecond pulses also have significant applications in optical fields,such as high spatial resolution LIDAR Thomson scattering diagnostics,space optical communication,laser material processing,laserinduced plasma generation and so on.Currently,the technology of pulse width compression in time domain based on stimulated Brillouin scattering(SBS)is the most effective means of obtaining sub-nanosecond pulses,and it has the advantages of achieving high pulse compression ratio,high energy conversion efficiency,capable of working at different wavelengths,simple structure,high feasibility and optical phase conjugation.In the experiment of self-excited SBS pulse duration compression of nanosecond pump,only with relative low incident energy,self-focusing and optical breakdown effect arising near the laser focus,as well as the broadening phenomenon of output hundred picosecond Stokes light due to its inappropriate interaction position with the pump can be effectually prevented,restricting the energy extraction efficiency of Stokes pulse;while the seed-injected Brillouin amplification technology makes it possible to further improve the power of hundred picosecond pulses with low energy.In this paper,the technologies of SBS pulse duration compression and active Brillouin amplification are united in order to attain high peak power hundred picosecond pulses without obvious modulation in waveform,and the major researches are as follows:Theoretically,the model describing interaction between pump and Stokes light is established on the basis of one-dimensional SBS coupled wave equation.Numerical simulations in respect of the two processes of SBS self-excited pulse compression and hundred picosecond seed-injected Brillouin amplification,are carried on by analyzing influences of laser parameters,medium parameters and spatial structure parameters on characterization parameters including energy conversion efficiency,output laser pulse width,rising edge,and temporal waveform,etc.The feasibility of obtaining hundred picosecond laser with high power has been verified,and the selected range for subsequent experimental parameters has been determined combined with calculated results.Experimentally,FC-770 with moderate parameters was selected as Brillouin medium,fundamental frequency single-longitudinal-mode pump laser with pulse duration of 7.9ns was compressed via optimal single-cell SBS pulse compression.Thus sub-nanosecond small signal Stokes seed with pulse duration of 587 ps was obtained,further interacting with nanosecond laser and being amplified.A new parameter which can quantitatively illustrate the variation degree of Stokes pulse waveform before and after amplification was defined as waveform fidelity F,and the interval for excellent waveform fidelity was set as 0.88(27)F(27)1.08.Under the condition of the relative delay time between the peaks of two laser pulses was 1.45 ns,hundred picosecond laser output from the system had good performance on waveform fidelity and no severe pulse duration broadening,the highest Stokes peak power magnification of 4.51 was achieved in this experiment,correspondingly,the highest peak power of hundred picosecond pulse was 102.0MW and the intensity was 811.7MW/cm2.