A new technique for generating high energy sub-400 picosecond laser pulses is presented in this paper. The temporally super-Gaussian-shaped laser pulses are used as light source. When the forward pump is reflected by the rear window of SBS cell, the frequency component that fulfills Brillouin frequency shift in its sideband spectrum works as a seed and excites SBS, which results in efficient compression of the incident pump pulse. First the pulse compression characteristics of 20th-order super-Gaussian temporally shaped pulses with 5 ns duration are analyzed theoretically. Then experiment is carried out with a narrow-band high power Nd:glass laser system at the double-frequency and wavelength of 527 nm which delivers 5 ns super-Gaussian temporally shaped pulses with single pulse energy over 10 J. FC-40 is used as the active SBS medium for its brief phonon lifetime and high power capacity. In the experiment, the results agree well with the numerical calculations. With pump energy of 5.36J, the compression of pulse duration from 5 ns to 360 ps is obtained. The output energy is 3.02 J and the peak-power is magnified 8.3 times. Moreover, the compressed pulse shows a high stability because it is initiated by the feedback of rear window rather than the thermal noise distributing inside the medium. This technique of generating high energy hundred picosecond laser pulses has simple structure and is easy to operate, and it also can be scaled to higher energy pulse compression in the future. Meanwhile, it should also be taken into consideration that in such a nonfocusing scheme, the noise-initiated SBS would increase the distortion on the wavefront of Stokes beam to some extent, and the pump energy should be controlled below the threshold of noise-initiated SBS.

We present a method for measuring the threshold of stimulated Brillouin scattering (SBS) when a large-aperture laser pulse with ultra-Gaussian shape is used as the pump source. By using an optical aperture to filter out part of the backward scattered light, the measured energy efficiency will be conserved below the SBS threshold and nonconserved above the SBS threshold. Based on the differences between the two conditions we can judge whether the pump intensity is above the SBS threshold or not by analysis of the energy efficiency of the system. The experiment is carried out with an Nd:YAG laser, delivering an ultra-Gaussian-shaped pulse with the pulse width of 3 ns, beam diameter of about 20 mm, and wavelength of 527 nm. Heavy fluorocarbon liquid FC-770 is adopted as the nonlinear medium. The measured SBS threshold under this condition is $634\mathrm{MW}/{\mathrm{cm}}^2$ and it has a good correspondence with the theoretically calculated results.

We present a novel method for measuring the threshold of stimulated Brillouin scattering (SBS) from the waveform of reflected light with large-aperture super-Gaussian-shaped laser pulses.