Study On Stimulated Rotational Raman Scattering Of High-power Laser Beams In Long Air Path

In the inertial confinement fusion (ICF), to achieve optimum fuel compression, the laser beams must irradiate the target uniformly, requiring excellent beam quality. But the effect of stimulated rotational Raman scattering (SRRS) will influence the power of laser and beam quality. At the case of excess of stimulated rotational Raman scattering threshold, not only the beam quality of the wave front will be degraded, but also the energy will be lost in process of high-power laser propagation in long air path. In this thesis, the factors that influence the threshold of SRRS effect and the laser beam quality have discussed in detail. The main results obtained here can be summarized as follows:(1) The physical model of SRRS in long air path has been built up.The physics model of SRRS have been built up, which considered the diffraction effects of stokes and pump lasers, Langevin noise sources, pulsed-shaped laser beams, the nonlinear polarization of the medium, the depletion of pumped laser, the nonlinear amplifier of the Stokes field, and the Raman bandwidth etc.(2) The simulation code of SRRS effect in long air path has been built up and verified.The simulation code of SRRS effect in long air path has been built up andverified in the use of the experimental and modeled data for Omega presented by Rochester University, showing the validity of our code and the simulation method.(3) The characteristics of SRRS effect in long air path have been studied.The factors that influence threshold of SRRS effect, such as the intensity of pump laser, pulse width, phase modulations in the time and the diffraction effect have been discussed in detailed. The effect of the factors including the intensity of pump laser, pulse width, phase modulations in the time and the diffraction effect on the propagation distance corresponding to the stokes threshold and conversion efficiency of stokes beam have been analyzed and discussed. In order to decrease the effect of SRRS effect on high-power laser in long air path, the methods that can restrain the SRRS effect have been proposed (4) The factors that influence the beam quality have been studied.The factors including SRRS effect, diffraction effect, hot spots, and so on that influence beam quality have been discussed in detailed. The methods that can improve the beam quality have been proposed.