The scattering of light from light induced structures in liquids

Abstract

The development of the study of light scattering, from the early work of Stokes and Rayleigh to the modern investigations of non-linear stimulated scattering processes has been reviewed.The conventional theory of stimulated scattering has been extended to describe the scattering of an independent probe laser beam. This scattering is the result of the effect on the refractive index of a medium of the electric field due to two oppositely directed, high intensity light beams. The standing wave of electric field, generated by these beams, spatially modulates the refractive index of the medium by electrostriction, the Kerr effect and absorptive heating, all of which arc proportional to the mean square of the local field. When the beams are of slightly different frequency the standing wave, and the resulting modulation, travel through the medium with a velocity proportional to that difference. Under these circumstances the modulation and the standing wave travel through the medium with the same velocity but with different phase as a result of the inertia associated with each of the above mechanisms. The usual stimulated scattering is determined entirely by the out of phase component of the refractive index modulation while the probe scattering described in this thesis is determined by the whole amplitude of that modulation.A Q-switchd ruby laser has been used to generate such modulations in a liquid and these have been detected by the scattering of a frequency doubled portion of the ruby laser beam and of an independent argon laser beam. The refractive index modulation associated with the temperature modulation induced by absorption of the ruby laser light has Leen investigated in some deta.il and the lifetimes of such modulations in a number of media have been measured. Other related non-linear scattering processes have been investigated using a variety of experimental techniques, particularly interesting results being obtained in the study of non-linear fluorescence from saturable absorbers.