title: Hidden reservoir of photoactive electrons in LiNbO3 crystals.
abstract: We show that a continuous-wave (cw) pump beam at a wavelength of 532 nm produces substantial light-induced (LI) absorption in the visible range in initially transparent undoped LiNbO3 crystals. The LI absorption coefficient stays linear in the pump intensity I(p) up to I(p)(max)=48  kW/cm2. Together with other features including long-term stretched-exponential relaxation of the LI absorption, it indicates that the present concept of LI electron processes in this important optical material must be revised: the amount of photoactive electrons increases already within the cw intensity range. A quantitative model is proposed that explains the experimental data and employs two-step excitations from filled localized states near the valence band via intermediate deep centers into the conduction band. The introduced localized states serve as a hidden reservoir of electrons.
authors.affiliation: Institute of Physics, University of Bonn, Wegelerstrasse 8, 53115 Bonn, Germany. luedtke@physik.uni-bonn.de
authors.forename: F
authors.initials: F
authors.lastname: Luedtke
authors.forename: K
authors.initials: K
authors.lastname: Buse
authors.forename: B
authors.initials: B
authors.lastname: Sturman