Secondary ion mass spectrometry study of space-charge formation in thermally poled fused silica

Applying a dc electric field across a fused silica sample at elevated temperatures followed by cooling the sample with the field applied (thermal poling) leads to a second-order nonlinearity that has been linked to the formation of a space-charge region in bulk glass. The first microscopic information on the extent of the space-charge region and its behavior with poling time is reported using secondary ion mass spectrometry to monitor the distribution of charged impurities. Lithium and sodium ions are observed to form depletion regions. Potassium and sodium ions as well as a hydrogenated species appear to be injected from the surface. The extent of the space-charge region evolves approximately logarithmically with poling time well after the nonlinearity as measured by second-harmonic generation has been established. The evolution of the space charge region can be qualitatively understood by an ion-exchange model that allows interaction of two ionic carriers with vastly different mobilities. (C) 1999 American Institute of Physics. [S0021-8979(99)02524-4].