The nonlinear refractive index of glass

The general theory of the third-order electronic susceptibility has been specialized to some model systems in order to evaluate the associated nonlinear refractive index of solid materials. The results indicate oppositely signed terms of comparable magnitude, and it is found that the dominant positive contribution involves oscillator strengths connecting excited electronic levels. Some reported values of the nonlinear index n2for various glasses are discussed in relation to the model calculations.