Spatially homogeneous spectral broadening of Yb lasers with field mapping beam shaping optics.

Yb:YAG thin disk lasers can deliver high average power, high-energy pulses of fundamental mode. To achieve spatially homogeneous spectral broadening of the pulses in a compact setup, we propose utilizing a thin-film compression (TFC) scheme following beam shaping via field mapping optics. In our proof-of-principle experiment, the pulse from a Yb:YAG laser was converted from a Gaussian beam to a nearly flat-top beam by a π-shaper. The spectral width of the pulse was broadened from 3.1 nm to 6.6 nm after accumulating nonlinear phase shift in a YAG crystal. This technique resulted in high spectral homogeneity and mitigated degradation of focusability typically observed after spectral broadening. We believe this approach offers a promising solution for the post-compression of high-energy Yb lasers within a compact setup.