Second harmonic generation and Raman study of second-order nonlinearity in PbO/B2O3 glass

The Maker fringe patterns of second harmonic generation (SHG) signals were measured in 0.43PbO/B2O3 glass samples poled at 2.5, 4.0 and 5.5 kV with a constant poling temperature of 400degreesC and a poling time of 120 min. By fitting theoretical Maker patterns to the experiment, a relationship between the thickness of the nonlinear layer in the glass sample and the poling voltage was obtained. By observing the change of polarised Raman spectra of samples before and after thermal poling, information was obtained regarding the structural origin of the second order nonlinearity (SON) in a lead borate glass. Compared with the normalised peak at 1350 cm(-1) before poling, the band intensity at 770 and 980 cm(-1) increased after poling. After poling, the band intensity at 980 cm(-1) in the VV spectrum, in which the polarisation of both the incident and the scattering lights are parallel to the direction of applied poling electric field E-P, is higher than that in the HH spectrum, in which the polarisation of both are vertical to E-P It was found for the first time that the asymmetric three coordinated borate units in the diborate groups play an important role in the SON of lead borate glass.