Second-Harmonic Generation from Thermally Poled Mixed Alkali Silicate Glasses Containing Various Alkaline-Earth Oxides

Abstract

Second-harmonic generation (SHG) was observed from thermally poled alkaline earth containing mixed alkali silicate glasses. Since no SHG could be observed in alkaline-earth oxide-free glasses, it was considered that alkaline-earth oxide played a significant role in the generation. The intensity of SHG increased with the time and applied voltage of poling. However, no oscillation fringe pattern was observed even in the glasses poled most intensively in the present work, at 3 kV for 6 h, which indicates that the poled layer is limited near the surface area and thinner than the coherent length. On the basis of IR reflection spectroscopy and electron probe microanalysis (EPMA) data, the SHG was related to the positive ion depletion immediately beneath the glass surface on the anode side. From the finding that the migration of cations or ion depletion on the anode side was larger in the glass containing larger alkaline-earth ions, it was considered that the large migration reduced the space charge gradient and resulted in a lower SHG intensity.