Dielectric relaxation induced by a space charge in poled glasses for nonlinear optics

Unpoled and efficient nonlinear optical (NLO) poled sodium niobium borophosphate glasses have been studied by means of dielectric spectroscopy. The thermal poling process induces a dielectric relaxation that gradually vanishes on heating for T greater than or similar to 500 K. The data are interpreted by a two-layer (Maxwell-Wagner) model, consisting of a bulk and a Na+ poor surface layer with lower conductivity. Our results suggest that the ion transport is due to hopping mechanism implying at least Na+. All the dielectric results are in full agreement with previous optical analyses. This is an example of poled glasses where an efficient NLO response is directly correlated to the conductivity of the material enhanced by a high alkali loading. (c) 2006 American Institute of Physics.