Experiment study of narrow pulse width and high repetition frequency laser amplifier

A compact, lower cost, angular multiplexing multi-pass slab amplifier is reported. The traditional rod structure has serious optical distortion, including thermal focusing, double focusing caused by stress, stress birefringence. The slab structure can reduce the impact of these effects, and improve the quality of laser beam. The slab laser geometry permits efficient use of the unsaturated gain medium by using angular multiplexing. Standard methods, such as polarization multiplexing, require the beam to be near to retrace its path. This retracing can result in feedback into the oscillator source and will, lead to parasitic oscillation of the amplifier. These problems due to retracing its path can be reduced if using angular multiplexing. A passively Q switched laser with repetition frequency of 20 kHz, pulse duration of 2.5 ns and average output power of 0.5 W is used as the master oscillator. Comparing the two ways of three-pass amplifications, we realize a method to effectively amplify the seed laser with nanosecond pulse duration and microjoule energy. When the seed laser is totally reflected in the Nd:YVO4 slab, the average output power of 3.2 W is achieved. Compared with other methods, this method can obviously eliminate the thermal lensing effect and enhance the output power.