Stokes Amplification Regimes in Quasi-cw Pumped Hydrogen-Filled Hollow-Core Photonic Crystal Fiber

Pure rotational stimulated Raman scattering spectra containing nine strong spectral components were generated from a $\sim 11\mathrm{m}$ long hollow-core photonic crystal fiber filled with hydrogen and pumped with nanosecond pulses having energies around 100–300 nJ. Observation of both transient and steady-state scattering threshold behavior is reported. Passage from the transient to the steady state is observed with a pulse as long as 14 ns. Convenient analytical expressions for energy and power threshold are deduced for the present configuration.