Raman-driven spectral broadening in a molecular gas-filled multi-pass cell with bulk compression to 15 fs

We report on Raman-driven spectral broadening and red-shifting in a molecular gas-filled multi-pass cell (MPC) for few-cycle pulse generation from a Yb:fiber chirped pulse amplification system. 1 mJ energy pulses at 1032 nm and 20 kHz are injected into a Herriott-type MPC filled with N₂O and He at 0.4 bar and 0.6 bar pressure, respectively. Raman-dominated spectral broadening produces a 0.9-1.45 µm spectrum with >80% of the energy shifted to longer wavelengths, resulting in a central wavelength >1200 nm, at 10.5 W average power and near-diffraction-limited beam quality. The Raman-induced negative spectral phase enables simple bulk compression to 15 fs, yielding a compact source for subsequent strong-field experiments.