Experimental study of the origin of the second-order nonlinearities induced in thermally poled fused silica

Second-harmonic generation (SHG) experiments at the surfaces and in the volumes of thermally poled commercial fused-silica samples have been performed. The experimental results show, for the first time to our knowledge and in agreement with our model, that second-order nonlinearity is induced on both cathodic and anodic interfaces. No contribution from the bulk of the sample could be detected. Moreover, our data also reveal that reorientable moieties are at the origin of the induced nonlinearity. The second-order susceptibility, evaluated by a surface SHG experiment, is chi((2))(333) similar to 1 pm/V. The estimated susceptibility associated with the dc Kerr effect is negligible. (C) 1997 Optical Society of America.