[en] Transient light-induced absorption changes α_li(t), caused by optically generated small polarons, are investigated in LiNbO₃:Mg below and above the optical-damage-resistance threshold (ODRT). The lifetime of α_li(t) is reduced by three orders of magnitude above the ODRT while a significantly enhanced amplitude α^max_li is observed in the infrared. Our observations are in full accordance with the predictions of microscopic models for the ODRT, namely the removal of Nb_Li antisite defects upon incorporation of Mg ions, and an enhanced dark conductivity. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (Abstract Copyright [2008], Wiley Periodicals, Inc.)

[en] The number densities and absorption cross sections of both optically generated and reduction-induced small electron and hole polarons in LiNbO₃ are determined by means of time-resolved pump-multiprobe spectroscopy. The data are obtained for free (Nb_Nb⁴⁺) and bound (Nb_Li⁴⁺) electron polarons, bound Nb_Li⁴⁺:Nb_Nb⁴⁺ electron bipolarons, and bound O^- hole polarons. The peak absorption cross sections are in the range of σ_pol∼(4-14) x 10^-22 m², comparable to that for Fe²⁺. In all cases the ratio of occupied to unoccupied polaronic sites is less than 10^-2.