STUDY ON THE OPTICAL SECOND-ORDER NONLINEARITY OF SUBMICROSPHERICAL SILICA GLASS

Undoped and Ce-doped silica submicrospheres are prepared by using the sol-gel method. The gel-like glass becomes thin glass plates by means of heat drying and densification. The nanospheres with diameters between 200 to 300 nm are sediment to an ordered layer of close-packed structure. Before measuring the optical second harmonic generation (SHG), samples are processed either by laser poling or thermal poling. Compared with fused silica glasses, the sample has a lower laser damage level. The submicrospheres inhibit from SHG for its centrosymmetric structure. Samples subjected to thermal poling at a temperature of 1050°C under a bias of 5kV for four days reveal an illustrious SHG. The X-ray diffraction pattern indicates an alternation of structure from nanocrystalline to amorphous, then to a close-packed cluster of SiO2 nanospheres as the thermal annealing temperature increases from 800 to 1050°C.