Effect of sodium addition and thermal annealing on second-order optical nonlinearity in thermally poled amorphous Ta2O5 thin films

We demonstrate second-order optical nonlinearity (SON) induced in amorphous tantalum pentoxide (Ta2O5) films by thermal poling. The effects of sodium addition and thermal annealing on the efficiency and stability of second harmonic generation (SHG) have been investigated. Maker fringe analysis has been used to quantify the poling-induced SON. χ(2) of 0.46 ± 0.02 pm/V and 0.34 ± 0.02 pm/V was achieved for sodium-containing and pure Ta2O5 films, respectively. Both the strength and the temporal stability of the induced nonlinearity are discussed with respect to the poling mechanisms and measured electrical conductivity. The lower density of uncombined charges of the Ta2O5 thin films is believed to play a role in the strength of SHG signal, and the rate of SHG decay decreases with thermal annealing.