Multipass Spectral Broadening of Spatially Chirped Pulses

External pulse compression using a multipass gas cell (MPC) is an extremely powerful technique for shortening the duration of sub-ps laser pulses [1]. Despite its tremendous success and versatility, the MPC method faces a challenge of handling high energy due to an unfavourable geometrical scaling requiring a rapid increase of the distance separating concave mirrors, and the corresponding size of the vacuum chamber. In this contribution, we propose and experimentally demonstrate the feasibility of reducing the MPC length relative to the target pulse energy by arbitrarily increasing the beam spot sizes on the mirrors, which is achieved through adding a spatial chirp on the collimated output beam from a grating-pair pulse compressor in a fs Yb CPA system.