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.

Figure 1

(a) Transmission spectrum of a 20 m long HC PCF (right-hand side axis) and the loss spectrum of the HC PCF (left-hand axis). (b) The SRS spectrum transmitted through $\sim 11\mathrm{m}$ of HC PCF filled with hydrogen and pumped with 13 ns pulse width and peak power of $\sim 300\mathrm{W}$.

Figure 2

Evolution of the average transmitted power of the different Raman spectral components as the coupled pump energy is varied. The pulse width of the pump is 13 ns.

Figure 3

Energy threshold of the pump for the generation of the first Stokes $S_{00}(1)$ as a function of the pump pulse width. The solid circles represent the experimental data. The dashed and dotted lines show the theoretical threshold for the transient and the steady-state regimes, respectively. The solid line is a linear fit for the data corresponding to pulse width greater than 14 ns.

Figure 4

Temporal profiles of the different transmitted pulses. (a) The temporal profile of 7 ns wide input pulse before entering the fiber, (b) the depleted pump, (c) the first-order Stokes, and (d) the second-order Stokes of the $S_{00}(1)$ Raman transition.