Simple, ∼95%-efficient, single-pass pulse compressor for Yb lasers using molecular gas nonlinearity.

We demonstrate 95% efficient pulse compression of 0.94 mJ, 160 fs pulses from a Yb laser to 36 fs using a simple, single-pass nitrogen-filled gas tube. The approach exploits both the instantaneous electronic and delayed rotational (Raman) nonlinearities of molecular gases to drive spectral broadening via self-phase modulation. For similar pulse durations, compared to hollow-core fiber and multi-pass cell methods, our single-pass, molecular-gas-based approach offers competitive throughput in a simpler alignment-insensitive setup while maintaining stable beam pointing and high polarization contrast. As a demonstration, we utilize the compressed pulses to generate broadband terahertz (THz) via optical rectification in GaP, achieving a ∼30% increase in THz spectral bandwidth relative to the uncompressed case.