Optical Microscopy, SHG, Polarized micro-Raman and IR Reflectivity Characterization
of Thermally Poled Sodium-Niobium Germanate Glasses
Glass surface before and after thermal poling as obtained on a x100 confocal optical microscope used for micro-Raman spectroscopy.
Thermal poling of a sodium-niobium germanate glass leads to the development of a thin layer with NLO properties, as manifested by the second harmonic generation Maker-fringe pattern measured for pp polarization.
Isotropic (a) and anisotropic (b) micro-Raman and IR reflectivity spectra (c) of a sodium-niobium germanate glass before (black lines) and after thermal poling (red lines). The vibrational spectra show that thermal poling induces structural changes in a thin glass layer under the anode. The thickness of this layer, as well as the depth-profile of the refractive index, can be evaluated from simulations of interference fringes observed in the high frequency part of IR spectra, see inset in (c). These findings allow correlations between thermal poling parameters (temperature, applied electrostatic field, duration and atmosphere) and second harmonic generation efficiency.