Temperature effect on self-focusing of laser beam in liquids

Abstract

Summary form only, as given. The interaction of light with acoustic excitations and molecular orientational excitations in liquids, a generalization of electrostrictive and optical Kerr effects, can lead to self-focusing of a laser beam. This gives rise to inhomogeneity or formation of hot filaments in the beam, and consequently, to many anomalous effects in the stimulated Raman scattering. The effect can be seen indirectly by the reduction in the Raman threshold of a Ramanactive medium with the insertion of a liquid cell in front of it. Experimental results show that the self-focusing effect occurs in both Raman-active and Raman inactive media, but is much stronger in liquids with large optical Kerr constants. Turbulence in the liquid cell also helps the self-focusing effect appreciably. It is therefore believed that the self-focusing of the beam is initiated by small-scale fluctuations in the refractive index of the liquid and in the laser intensity, and perpetuated through either the electrostrictive, or the optical Kerr effect, or both.