Subpicosecond Laser Spectroscopy of Blue-Light-Induced Absorption in KNbO_3 and LiNbO_3

摘要

Pulses of 427-nm light from am amplified Ti:sapphire frequency-doubled laser are absorbed in two-photon band-gap excitations of KNbO_3 and LiNbO_3. Induced absorption spectra measured in the visible and recently extended in the infrared have been recorded as a function of delay from 0 to 250 ps after two-photon blue excitation. Samples include stoichiometric as well as congruent LiNbO_3. Comparison is made to transient absorption in the nanosecond and longer time range induced by electron pulses of approx 10 ns width and 270 keV energy. Parts of the absorption can be attributed to bound and free polarons, including thei ntrinsic electron polaron.