Second-harmonic generation from thermally poled mixed alkali silicate glasses containing various alkaline-earth oxides

Second-harmonic generation (SHG) was observed from thermally poled alkaline earth containing mixed alkali silicate glasses. Since no SHG could be obse rved in alkaline-earth oxide-free glasses, it was considered that alkaline- earth oxide played a significant role in the generation. The intensity of S HG increased with the time and applied voltage of poling. However, no oscil lation fringe pattern was observed even in the glasses poled most intensive ly in the present work, at 3 kV for 6h, which indicates that the poled laye r 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 b eneath the glass surface on the anode side. From the finding that the migra tion of cations or ion depiction on the anode side was larger in the glass containing layer alkaline-earth ions, it was considered that the large migr ation reduced the space charge gradient and resulted in a lower SHG intensi ty.