Induction and relaxation of optical second-order nonlinearity in tellurite glasses

Second harmonic generation has been examined for 30ZnO . 70TeO(2) glass with a two-step poling procedure in order to understand the poling temperature dependence of second harmonic intensity. When the poling temperature increases, the second harmonic intensity increases, manifests a maximum at the temperature which we call an optimum poling temperature, and decreases drastically just below the glass transition temperature. The glass treated with two-step poling, which includes poling at 300 degrees C and subsequent poling at the optimum poling temperature, i.e., 280 degrees C, exhibits much smaller second harmonic intensity and more unambiguous Maker fringe pattern than that poled only at 280 degrees C. This fact suggests that the decrease in second harmonic intensity with an increase in poling temperature cannot be attributed to a reversible process like a thermal fluctuation of dipoles, but is governed by an irreversible one. Based on a linear relation between the optimum poling temperature and glass transition temperature, the irreversible process is deduced to consist of some oxidation reactions such as a migration of nonbridging oxide ions to and subsequent evaporation of oxygen gas at the anode side. Decay of the second harmonic intensity for 30NaO(1/2). 70TeO(2) glass as well as 30ZnO . 70TeO(2) glass has also been examined at room temperature. Whereas the 30ZnO . 70TeO(2) glass does not show a decay, the second harmonic intensity of the 30NaO(1/2). 70TeO(2) glass decays rapidly with an average relaxation time of 10 h. This relaxation behavior is explainable in terms of the difference in mobility between Zn2+ and Na+ ions. (C) 1999 American Institute of Physics. [S0021-8979(99)04704-0].