Angular bandwidth for the non-focusing stimulated Brillouin scattering pulse compression

Laser pulse duration compression by stimulated Brillouin scattering (SBS) with a non-focusing scheme is a suitable candidate for high energy sub-nanosecond pulse generation owing to its high load capability and simple structure. The angular deviation of the feedback seed from the pump light path has a serious impact on the non-focusing SBS pulse compression. In this paper, we study the influence of this effect both numerically and experimentally. Firstly the pulse compression characteristics of 20th-order super-Gaussian-shaped pulses with 5 ns duration are analyzed theoretically. Then an experiment was carried out with a single-frequency high power Nd:glass laser system at the frequency-doubled wavelength of 527 nm which delivers 5 ns super-Gaussian-shaped pulses with single pulse energy over 10 J. Heavy fluorocarbon liquid FC-40 was used as the active SBS medium. The compressed pulse duration of sub-400 ps with an energy efficiency of similar to 50 % is obtained when the laser is normally incident on the rear cell window. +/- 4 degrees deviation between the feedback Stokes light and pump laser halves the energy efficiency and doubles the compressed pulse duration. The experimental results agree well with the numerical calculations. The results of this paper will provide a basis for the design of self-pumped SBS pulse compressor and pave a way for higher energy sub-nanosecond pulse generation in the future.