Measurement of the coefficient of electronic nonlinearity in optical and laser glass

Abstract

The electronic nonlinearity coefficient n2 of transparent dielectrics was determined by direct observation of the self-focusing of smooth single-mode nanosecond laser pulses. The critical self-focusing power for glass of a given type Pcr was found from a series of measurements of the threshold power Pth for different effective specimen lengths Leff = zsf, thus eliminating errors associated with the determination of the beam width. The required set of zsf values was obtained by varying the focusing or defocusing of the radiation on the entrance face of a single specimen. The experimental dependence of Pth1/2 on (zsf?1), enabling Pcr to be determined by the intercept on the ordinate axis, was only linear up to some value of P above which the regular self-focusing pattern was disrupted by the development of transverse perturbations. Data on Pcr and n2 were obtained for some Soviet glasses (KGSS 1621, GLS 1, LGS 247).