Theoretical analysis of uniform longitudinal gain for a double-end-pumped Yb:YAG multi-slab pulsed amplifier

For high average power lasers with double-end-pumped multi-slab (DEPMS) configuration, a non-uniform gain distribution within each slab caused by the step-doped multi-slab will lead to the amplified spontaneous emission (ASE) effect and then reduce the laser performance. As an example, longitudinal gradient doping is used in a DEPMS Yb:YAG pulsed amplifier to create uniform longitudinal gain (ULG) and then the ASE effect is effectively reduced. The ULG is theoretically derived and we show that the energy storage can be increased by 9% with ULG compared with the step-doped DEPMS. We found that the optimal pump efficiency, longitudinal gain-length product and columnar doping density are determined by the launched pump intensity. Numerical simulation also demonstrated that optimization of the amplifier with uniform gain and high pump efficiency can be achieved by placing additional gradient slabs to the original gradient doping slabs. Our investigations might provide an efficient way to carefully optimize a DEPMS pulsed amplifier with higher efficiency.