Plasma-induced spectral broadening of high-energy ultrashort laser pulses in a helium-filled multiple-pass cell

We investigated the possibility of plasma-induced spectral broadening of high-energy ultrashort laser pulses in a helium-filled multipass cell (MPC) through a series of full numerical simulations of the extended nonlinear Schrodinger equation. It was found that the gas pressure must be set low so that the propagation dynamics can be controlled only by plasma defocusing. Simulations using 100 mJ, 40 fs laser pulses in the MPC, which is 6 m long and has a mirror of 3.1 m radius at each end, showed that if the gas pressure is set within the range of 40-130 Pa, then the relevant spectral broadening can be obtained after five passes, yielding compressed pulses of a 4.7-6.4 fs width. The ratio of the energy of the compressed pulse to the output pulse is found to be within 58-88%.