A group of scientists at Bath University in the UK have reduced the threshold power for stimulated Raman scattering by nearly two orders of magnitude using a photonic crystal fiber. Fabricated by capillary-stacking techniques, the fiber guided 6-ns, 532-nm laser pulses down its 15-µm hollow core.The group permeated the core with pressurized hydrogen gas, which served as the Raman active medium and demonstrated a threshold for Stokes generation at pulse energies down to approximately 800 nJ. The threshold for anti-Stokes generation was approximately 3.4 µJ, and the pump-to-Stokes conversion efficiency was approximately 30 percent at 4.5-mJ pulse energies.The work appeared in the Oct. 11 issue of Science.