Model for thermal/electric-field poling of fused silica

Using the multiple-carrier model, the process for thermal/electric-field poling in the fused silica is analyzed. The depletion region is proved to be composed of a positive charged layer, an ionosphere layer and a negative depletion layer. The space-charges in two former layers are H3O+, O+, Al++ and others, and the space-charge in the latter is drop Si--O-. The thermal stability of the depletion region is determined by the strength of the ionosphere. In addition, the ion density distribution in the depletion region is derived. The results show that both the positive and the negative space-charge layers are approximately well-distributed, and the self-built electric field in the depletion layer is approximately distributed in triangle-form, the maximum of which is located inside the sample. This model proves that the second order susceptibility and the conversion efficiency of the second harmonic are proportional to the square-root and square of the applied de voltage, respectively.