Second-order optical nonlinearity and accompanying near-surface structural modifications in thermally poled soda-lime silicate glasses

Abstract

Soda-lime silicate (SLS) glasses were thermally poled at 230°C-280°C with dc voltages up to 2kV applied to induce a second-order optical nonlinearity. Accompanying structural modifications to the thermally poled SLS glasses were investigated with scanning electron microscopy. On the cathode surface, sodium metasilicate crystals were formed through the reduction of migrating sodium ions at the cathode. At the anode, intense phase separation occurred within several micrometers beneath the anode surface during the thermal poling process. These structural modifications are attributed to the electric field enhancement effect. The second-order nonlinearity induced in such poled samples was found to still be present after a long period of high-temperature annealing, perhaps mainly due to a hindering effect from the phase separation and/or accumulated calcium ions to the recombination of space charges.