Space charge dynamics in thermally poled fused silica

Measurements of the transient behavior of both the second-harmonic generati on signal and the poling current for type-II fused silica samples under a v ariety of poling histories are reported. The applied voltage was switched b etween +5 kV, 0 V, and -5 kV with the sample maintained at 275 degrees C. O bservations include: multiple time scales (seconds to minutes) for developm ent of the non-linearity depending on the poling history; a transient secon d-harmonic signal on the new cathode side of the sample following voltage r eversal; and hysteretic incubation intervals before growth of the non-linea rity. These observations are incompatible with the usual single mobile ion (e.g. Na+) model for establishing the strong local electric field that lead s to the non-linearity. An expanded model including ion-exchange between a high mobility ion (as Na+) and a much lower mobility ion (related to H+) pr ovides a good qualitative fit to the experiments, (C) 1998 Elsevier Science B.V. All rights reserved.