Raman-limited beam diameters in the self-focusing of laser light

Abstract

Numerical calculations show that high conversion of laser light into stimulated Raman light in the forward direction limits the beam diameter of the self-focused light. The dependence of the limiting diameter on material parameters and experimental conditions is calculated. In the experiments we used single-frequency laser pulses of \ensuremath{\sim} ${10}^{\ensuremath{-}8}$-sec duration. Our measured minimum diameters in liquid benzene, mixtures of benzene C${\mathrm{S}}_{2}$, and toluene are in fair agreement with values calculated from our steady-state theory. The rapid movement of the focus at the end of the liquid cell gives rise to transient stimulated Raman scattering or transient self-focusing in liquids with long relaxation times. In C${\mathrm{S}}_{2}$, nitrobenzene, and bromobenzene these transient effects have to be taken into account in the comparison between calculated and measured limiting diameters.