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Hidden reservoir of photoactive electrons in LiNbO3 crystals

: Luedtke, F.; Buse, K.; Sturman, B.


Physical review letters 109 (2012), No.2, Art.026603
ISSN: 0031-9007
ISSN: 1079-7114
Journal Article
Fraunhofer IPM ()

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/cm(2). 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.