Stimulated Raman scattering produced by self-focusing in liquid crystals.

Abstract

The Raman spectra in backscattering and the far-field patterns of the transmitted light through a nematic liquid crystal cell are studied simultaneously. It is shown that stimulated Raman scattering is produced when self-focusing of the beam takes place. The threshold for stimulated scattering can be varied by selecting different angles between the polarization of the laser beam and the director orientation, thus changing the threshold for self-focusing. By using a microscope objective and focusing the input light to a beam waist of 10 \ensuremath{\mu}m we observe stimulated Raman scattering at very low powers (\ensuremath{\sim}8 mW) in a thin nematic film (\ensuremath{\sim}100 \ensuremath{\mu}m) for some orientations of the cell. The possibility of observing self-focusing and stimulated Raman scattering with low powers in a cavityless medium such as this is due to the extraordinarily large optical nonlinearities of liquid crystals in the nematic phase. \textcopyright{} 1996 The American Physical Society.