1998 Volume 62 Issue 10 Pages 932-938
The mechanism of second-harmonic generation (SHG) was investigated for the thermal poled fused quartz and synthesized silica glasses. The current was measured for silica glasses during the thermal poling process. As a result, fused quartz with a relatively higher current generated SHG. We discussed the relationship between crystallization from glass to crystal and second-order nonlinearity, based on a continuous-heating transformation (C-H-T) diagram and the sample temperature, which was calculated from the Joule’s heat of the poling process. It was observed that grain size of the α-quartz and α-cristobalite crystal was about 20 nm at the depth at 5 μm from the anodic surface in the poled fused quartz (553 K, 4 kV, 103.56 s), by a field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD) analysis. The distribution of intensity of the second-harmonic (SH) signal was measured in a layer of SHG near the anodic surface. As a result the mechanism of SHG was deemed due to crystallization from silica glass to the orientated α-quartz possessing second-order nonlinearity under a high electric field and Joule’s heat in the thermal poling condition. It was considered that the intensity of SH signal was higher with increasing quantity of orientated nano-crystals, but was lower with decreasing orientation of the nano-crystals, but was lower with decreasing orientation of the nano-crystals, along with decreasing electric field.
