Spatio-spectral couplings in saturated collinear OPCPA

Ultrafast laser pulses featuring both high spatio-temporal beam quality and excellent energy stability are crucial for many applications. Here, we present a seed laser with high beam quality and energy stability, based on a collinear optical parametric chirped pulse amplification (OPCPA) stage, delivering 46 mu J pulses with a 25 fs Fourier limit at 1 kHz repetition rate. While saturation of the OPCPA stage is necessary for achieving the highest possible energy stability, it also leads to a degradation of the beam quality. Using simulations, we show that spectrally dependent, rotationally symmetric aberrations dominate the collinear OPCPA in saturation. We experimentally characterize these aberrations and then remove distinct spatial frequencies to greatly improve the spectral homogeneity of the beam quality, while keeping an excellent energy stability of 0.2 % rms measured over 70 hours. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

This article presents a seed laser with high beam quality and energy stability based on collinear optical parametric chirped pulse amplification (OPCPA) technology. Through experimental and simulation studies, the authors found that saturation of the OPCPA stage leads to a degradation of the beam quality, but the spectral homogeneity of the beam quality can be greatly improved by removing specific spatial frequencies.