STIMULATED RAMAN-SCATTERING PRODUCED BY SELF-FOCUSING IN LIQUID-CRYSTALS

The Raman spectra in backscattering and the far-field patterns of the transmitted light through a nematic liquid crystal cell are studied si multaneously. It is shown that stimulated Raman scattering is produced when self-focusing of the beam takes place. The threshold for stimula ted scattering can be varied by selecting different angles between the polarization of the laser beam and the director orientation, thus cha nging the threshold for self-focusing. By using a microscope objective and focusing the input Light to a beam waist of 10 mu m we observe st imulated Raman scattering at very low powers (similar to 8 mW) in a th in nematic film (similar to 100 mu m) for some orientations of the cel l. The possibility of observing self-focusing and stimulated Raman sca ttering 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.