Competition between stimulated Raman and Brillouin scattering processes in CF₄ gas

CF₄ gas has a relatively high Raman cross section and a relatively small Raman shift and is an excellent candidate for a gas-filled hollow-core photonic bandgap (HC-PBG) fiber Raman wavelength converter. Here we investigate experimentally the onset and competition between stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) processes in high-pressure CF₄ gas. We focus 532 nm laser pulses into a high-pressure gas cell and measure the SBS and SRS response. The thresholds for both processes decrease with pressure, as expected. However, with short focusing geometries, the SBS threshold is lower than the SRS threshold, and with long focusing geometries, it is the opposite. We further show that with HC-PBG fiber geometry SRS dominates.