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It is necessary for high power ultraviolet lasers to propagate through a long air path during experiments of inertial confinement fusion (ICF). When the product of gain efficiency and propagation distance is beyond the stimulated rotational Raman scattering (SRRS) threshold, the high power ultraviolet laser beam is subject to loss of energy and a decrease in beam quality, further resulting in the reduction of conversion efficiency of triple-harmonic, and even causing the optical components to be destroyed. This paper studies the four-dimension numerical modeling of SRRS effects, with emphasis on the variation of beam aperture and corresponding beam distributions in near field. The research showed that the variation of the pump beam aperture made little effect on SRRS transform efficiency ratio with the same incident energy and the same propagation distance, the transverse intensity distribution of beams became more even with an increase in the beam aperture. We have made the deduction that high power laser's SRRS effects through a long air path could be depressed by increasing the beam aperture on the condition of equal incident energy and propagation distance.

A prominent application of stimulated Brillouin scattering (SBS) is pulse sequence compression for obtaining high power and high intensity optical pulse. The characteristics and the stability of the compressed Stokes pulse were investigated using compact two-cell SBS phase-conjugation mirror. FC-770, having low absorption and high breakdown threshold at the wavelength of 1064 nm, was used as the SBS medium. Both the Stokes pulse width and the reflectivity were measured as a function of incident pump energy. In our work, a 8 ns laser pulse of 1064 nm generated by Q-switched Nd: YAG was optimally compressed to 116 ps for pump energies of 310 mJ, while the energy reflectivity is above 85%. The shortest pulses width obtained exhibit 99 ps duration. The stability of the temporal pulse widths after compression was investigated statistically. For non-optimal pump energies pulse widths become larger and the stability is found to decrease.

The performances of stimulated Brillouin scattering (SBS) media with short phonon lifetimes on temporal compression are studied in this paper. In the experiment, FC-72, HT-135 and FC-40 (phonon lifetimes are 1.2 ns, 0.4 ns and 0.2 ns, respectively) are used to study the influence of phonon lifetime on pulse compression in a compact two-cell SBS system. High pulse compression ratio is obtained by a medium with a short phonon lifetime when input energy is high. These results are useful in the generation of picoseconds pulse for Shock Ignition of thermonuclear fuel for ICF.