Polaron dynamics in lithium niobate upon femtosecond pulse irradiation: Influence of magnesium doping and stoichiometry control

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