DYNAMICS OF 2ND-HARMONIC GENERATION IN FUSED-SILICA

The temporal dynamics of the induced second-order nonlinearity in fuse d silica samples held at elevated temperature as an external electric field is switched on and off are monitored with second-harmonic genera tion experiments. Rise times vary from 138 to 5 s as the temperature i s varied from 207 to 267-degrees-C and are consistent with an Arrheniu s dependence with an activation energy of 1.3 eV. A similar result is found for the short-circuit fall time with an activation energy of 1.1 eV. In addition, weak oscillatory deviations from simple exponential dependences are observed. A model based on simple ionic charge transpo rt in combination with bond reorientation is introduced.