| Inertial Confinement Fusion(ICF) has drawn the attention of governments and academies because it is the candidate to solve the energy crisis. To manufacture more than 200 ps of the pulse width, kilojoule of the energy and dozens of TW of the single laser pulse peak power for the requirement of shock ignition, stimulated Brillouin scattering(SBS) pulse compression and amplifica-tion technology gradually walk into the vision. Stimulated Brillouin scattering which has the outstanding characteristics such as phase conjugation, high pulse energy conversion rate and high gain, is the most simple and practical compression method to realize shock ignition of high-power laser pulse. In this paper, picosecond pulse compression and amplification process have been studied and analyzed in detail from the two aspects of theory and experiment. To determine the influence of parameters to the SBS pulse compression and amplification process under the low energy, to provide the reference for the realization of the high-energy pulse amplification.Firstly, the spontaneous origin model and the physical model of Brillouin amplification are established according to the principle of stimulated Brillouin scattering. On the basis, Brillouin amplification theory model is derived according to Maxwell’s equations and Navier-Stokes equations. Using the approximation method of the amplitude which is slowly changed and the mathematical means to get the discrete theoretical formula. Then the influence of pump parameters, structure parameters and nonlinear dielectric parameters on the stimulated Brillouin scattering pulse compression and amplification process is simulated respectively. The compressed pulse width and energy reflectivity in the process of compression were studied. And the energy extraction efficiency, seed energy magnification and compression ratio of seed pulse were also studied.From the relationship of chemical structure and characteristics of SBS medium, new type fluorocarbon series medium is explored. The fluorocarbon series new SBS medium, such as PF-5060 and FC-43, FC-70, with high load, low absorption and short life is proposed and the chemical molecular structure is given. The phonon lifetime, gain coefficient and Brillouin frequency shift is given by theoretical calculation under 532 nm wavelength. And the absorption coefficient and the optical breakdown threshold is experimental measured.Adopting two-stage Brillouin compression structure, experiments are carried out to study the produce process of short pulses, on the basis of simulation results to determine the best structure parameters. The similar molecular structure of perfluori-nated amine series medium is chosen to carry on the comparative study. The influence rule of the medium phonon lifetime to the narrowest compressed pulse width, the compression waveform stability and energy reflectivity is studied. We get the conclusion that the smaller the phonon lifetime, the narrower the pulse width and the more good stability can be compressed in the same conditions. And then the perfluori-nated polyether series and perfluorinated hydrocarbon series medium which have bigger difference in molecular structure and phonon lifetime are selected to verify the above conclusion.Finally, according to the simulation results of amplifying theory, relying on the existing experimental equipment and conditions, Brillouin amplification process is experimental explored. Through the analysis of pump energy extraction efficiency, seed energy magnification and stokes pulse width compression efficiency three typical parameters, the functional rule of pump energy, seed energy, amplifier-cell length and medium parameters in stimulated Brillouin amplification process. The results showed that there are optimal values in amplifier-cell length. By increasing the pumping energy and reducing seed energy can obtain higher magnification. In the stage of low energy, the smaller the medium phonon lifetime, the higher the magnification of energy, the smaller the pulse width broadening. |
