The use of non-uniform filters with a controlled spatial absorption profile has improved the spatiotemporal profile of amplified signal and idler pulses in a two-stage parametric amplification scheme for femtosecond pulses. The measured dependence of the signal wave emission spectrum on the transverse coordinate reveals high homogeneity with suppression of the central part of the seed pulse beam, while the 2+1-dimensional numerical simulation of the parametric amplification process for femtosecond pulses predicts a corresponding increase in the homogeneity of the temporal profile of the signal and idler pulses and a decrease in their duration. The efficiency of the corresponding parametric conversion of submillijoule pulses reaches 50%.
Stepanov et al. (Sun,) studied this question.