Thermal poling of silica in air and under vacuum: The influence of charge transport on second harmonic generation

A comparison between thermal poling of silica in air and in vacuum is repor ted. It is shown that the second-order susceptibility and thickness of the nonlinear layer as well as their time evolution are highly dependent on the surrounding poling atmosphere. In the vacuum case a charge distribution (u nder the anode) more complex and broader than that for the air case has als o been revealed by laser induced pressure pulse measurements. A multiple ch arge carrier model can explain the formation and evolution of the depletion region under the anode. The findings are relevant to achieve improved nonl inearities in fiber and waveguide devices. (C) 1999 American Institute of P hysics. [S0003-6951(99)03617-7].