Comparative study of spectral broadening Yb laser pulses in gas-filled hollow-core fibers*

The limited gain bandwidth of Yb-based amplifiers has led to a demand for robust spectral broadening techniques that enable few-cycle pulse compression. We conducted a comparative study between several atomic and molecular gases as a media for spectral broadening in a hollow-core fiber geometry. By exploiting self-phase modulation, self-steepening, and stimulated Raman scattering, we explored the extent of spectral broadening and its dependence on gas pressure, the critical power for self-focusing, and the optimal regime for few-cycle pulse compression. We attained 17 fs pulses from 3-mJ, 200-fs input laser pulses with 80% transmission efficiency. Appropriate choice of gas parameters and fiber geometry enable the generation of few-cycle pulses for a variety of input pulse energies and durations.