Abstract

LiNbO₃ (LN) and LiTaO₃ (LT) are key materials for optical frequency conversions. The major issues of these materials were light-induced absorption (LIA) and photorefractive (PR) damage. It was revealed that the small bound polaron (an electron is trapped at the antisite defect) causes LIA and PR damage in congruent LN crystals [1,2]. The MgO doping eliminated the antisite defects and suppressed LIA and PR damage [3,4]. Nowadays, the application of these materials has been extended to frequency conversion of pulsed lasers. Here peculiar LIA issues come up. Even if the photon energy is less than the energy bandgap, the pulsed light causes two-photon absorption (TPA) and parasitic harmonic generations, that lead to carrier excitations. The carriers are trapped at polaronic states, inducing optical absorption. Recently, it has been revealed that a large absorption in the near infrared is optically induced in MgO doped LNs [5-7].

© 2011 IEEE