Comparative study on light-induced absorption between MgO:LiNbO3 and MgO:LiTaO3

A comparative study on the light-induced absorption was performed for lithium niobate and lithium tantalate crystals in which the antisite defects were eliminated by MgO doping. The induced absorption was measured in a spectral window ranging from visible to near infrared with a time resolution of 10 ns. Upon pulsed-light irradiation, a broad absorption peaking near 1250 nm was induced in MgO-doped lithium niobate. It was attributed to the small free polaron, an electron trapped at the regular Nb ion site. In contrast, such absorption in the near infrared originating from the free polaron was absent in MgO-doped lithium tantalates. The findings are highly relevant to the frequency conversion performances of high-power and pulsed lasers based on the current periodically-poled devices. The results also suggest guidelines for improving the crystal qualities.