Evidence of microscopic-scale modifications in optical glasses supporting second harmonic generation

Abstract

We explore, by means of inelastic neutron scattering, the extent of changes in dynamic correlations induced by thermal poling of vitreous SiO2. The measured vibrational density of states shows an excess of modes in certain frequency regions as well as a narrowing of the 100 meV peak. These findings indicate that such alterations cannot be ascribed to the appearance of new well defined vibrational modes, such as those coming from localized topological defects, but rather arises from an increase in ordering in the material as attested in a reduced spread of the inter-tetrahedral angles.

Mechanism of Thermal Charge Relaxation in Poled Silicate Glasses in a Wide Temperature Range (From Liquid Nitrogen to Glass Melting Temperature)

“…In poling of isotropic media, orientation of these dipolar groups under the applied DC electric field breaks the central symmetry of the medium and results in a material demonstrating a second harmonic generation (SHG). The latter is actually observed in poled glasses, − including the glass under study and other oxide glasses. − …”