Transient optical absorption upon femtosecond pulse irradiation in lithium niobate crystals

摘要

Formation and relaxation dynamics of electron polarons in lithium niobate crystals is investigated by measuring transient absorption induced by blue femtosecond pulses. Anisotropy in absorption change distinguishes between small free polarons and small bound polarons, revealing that the dynamics is influenced by MgO-doping and stoichiometry control. In crystals doped with MgO at concentrations above threshold, small free polarons are generated within 100 fs and decay at tens of nanosecond. In the presence of antisite defects, sequential formation of polaronic states occurs: electrons initially trapped as small free polarons become trapped as small bound polarons at picosecond time scale. The results are relevant for nonlinear optical applications of pulsed or high-power lasers.