EMERGENCE OF STRUCTURAL ANISOTROPY IN OPTICAL-GLASSES TREATED TO SUPPORT 2ND-HARMONIC GENERATION

Structural alterations induced by ''thermal poling'' in upsilon-SiO2, a treatment which enables the glass to double the frequency of impingi ng infrared light, are revealed by neutron diffraction to be a breakdo wn of macroscopic isotropy. This leads to concomitant changes in the v ibrational density of states measured by inelastic neutron scattering. The observations are consistent with emergence of partial ordering wi thin the glassy matrix along the direction of an electrostatic field a pplied during the poling treatment, [S0031-9007(98)07619-4].