title: Investigation of nonlinear absorption processes with femtosecond light pulses in lithium niobate crystals.
abstract: The propagation of high-power femtosecond light pulses in lithium niobate crystals (LiNb O3 ) is investigated experimentally and theoretically in collinear pump-probe transmission experiments. It is found within a wide intensity range that a strong decrease of the pump transmission coefficient at wavelength 388 nm fully complies with the model of two-photon absorption; the corresponding nonlinear absorption coefficient is beta(p) approximately = 3.5 cm/GW. Furthermore, strong pump pulses induce a considerable absorption for the probe at 776 nm. The dependence of the probe transmission coefficient on the time delay Delta t between probe and pump pulses is characterized by a narrow dip (at Delta t approximately = 0) and a long (on the picosecond time scale) lasting plateau. The dip is due to direct two-photon transitions involving pump and probe photons; the corresponding nonlinear absorption coefficient is beta(r) approximately = 0.9 cm/GW. The plateau absorption is caused by the presence of pump-excited charge carriers; the effective absorption cross section at 776 nm is sigma(r) approximately = 8 x 10(-18) cm(2). The above nonlinear absorption parameters are not strongly polarization sensitive. No specific manifestations of the relaxation of hot carriers are found for a pulse duration of approximately = 0.24 ps.
authors.affiliation: Institute of Physics, University of Bonn, Wegelerstr. 8, D-53115 Bonn, Germany. beyer@physik.uni-bonn.de
authors.forename: O
authors.initials: O
authors.lastname: Beyer
authors.forename: D
authors.initials: D
authors.lastname: Maxein
authors.forename: K
authors.initials: K
authors.lastname: Buse
authors.forename: B
authors.initials: B
authors.lastname: Sturman
authors.forename: H T
authors.initials: HT
authors.lastname: Hsieh
authors.forename: D
authors.initials: D
authors.lastname: Psaltis