Diode-pumped large-aperture Nd:YAG slab amplifier for high energy nanosecond pulse laser

A high gain, low thermal-induced wavefront distortion, laser diode-pumped Nd: YAG slab amplifier is demonstrated with its active media dimensions of 7  mm×35  mm×138.2  mm. Under the 200  Hz, 1440  W pulse pumping condition while no seed light to amplify, the thermal induced wavefront aberration of a He-Ne probe passing through the gain meUdium is 0.165 λ@633  nm (RMS). The amplifier shows stable aberration character with two major low-order terms, defocus and 0° astigmatism. The fluorescence distribution, stored energy, and small-signal gain of the amplifier are measured and have a good agreement with the calculated results. In the amplifier, the fluorescence is uniformly distributed and the maximum stored energy of 3.2  J can be achieved with a plane-concave cavity at 200  Hz pump repetition frequency. For a repetition frequency of 200  Hz, 25  μJ injection polarized seed-light and 1440  W pump power, the small signal gain reaches 9.45. The amplifier has been successfully employed in a 200  Hz, 5  J, MOPA system with 1.7 times diffraction limited output.