Asymmetry of the Forward and Backward Raman Gain Coefficient at 1.54 mum in Methane

Single-longitudinal-mode ring diamond Raman laser

We demonstrate a single-longitudinal-mode ring diamond Raman laser, pumped by a tunable single-mode Ti:sapphire laser. Two methods to achieving unidirectional operation have been demonstrated: increasing gain for one direction using a reinjecting mirror and increasing loss for one direction using sum frequency mixing in BBO. Both methods result in a stable single-longitudinal-mode operation.

Strong forward-backward asymmetry of stimulated Raman scattering in lithium-niobate-based whispering gallery resonators

We show experimentally and prove theoretically that the pump-power thresholds of stimulated Raman scattering (SRS) in lithium-niobate-based whispering gallery resonators (WGRs) are strongly different for the signal waves propagating in the backward and forward directions with respect to the pump wave. This feature is due to a strong polaritonic effect. It leads to a cascade of alternating forward-backward Raman lines with increasing pump power. The measured polarization and spectral properties of SRS are in good agreement with theory. Similar properties have to be inherent in other WGRs made of polar crystals.

Efficient Raman laser system using stimulated Brillouin scattering with different confocal parameters for CH(4)

We report the efficient Raman laser system with the wavelength of 1.54 microm from a passively Q-switched Nd:YAG laser with high-pressure methane gas. It has been known that the stimulated Brillouin scattering (SBS) prevents the Raman conversion. The efficiency of the Raman conversion, however, has been greatly enhanced with a specially designed lens to use a backward-stimulated Brillouin in our scheme. The special lens has a focal length of 12 cm, and a maximum conversion efficiency of 51% has been obtained with the first-Stokes energy of 32 mJ and the residual pump energy of 30 mJ at 1,400 psi. Comparing two resonators with different focal lengths of the lenses, we have found that backward-SBS can be greatly enhanced by use of the shorter focal length of 12 cm, and the enhanced backward-SBS helps to increase the conversion efficiency.