Berlin 2008 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 14: Electric, electromechanical and optical properties II

DF 14.8: Vortrag

Donnerstag, 28. Februar 2008, 16:20–16:40, EB 407

Self-induced fixing of index gratings in LiNbO₃:Fe using a single laser beam — •Volker Dieckmann, Andreas Selinger, and Mirco Imlau — Department of Physics, University of Osnabrück, Barbarastr. 7, D-49069 Osnabrück, Germany

Self-induced fixing of noisy refractive-index gratings is discovered in single crystals of iron-doped LiNbO₃ (0.1 wt.% Fe) upon long-term exposure to a single laser beam of high intensity (I= 100 W/cm²) at ambient temperature. The extraordinary polarized laser beam (λ=532 nm) impinges normal to the c-axis of the sample. At the beginning of exposure, this results in the recording of noisy refractive-index gratings and in a nearly symmetric angular intensity distribution in ± c-direction of scattered light (Goulkov et al., Phys. Rev. B, 65, 195111 (2002)). Further exposure to the high intense laser beam leads to a decrease of the scattered light intensity and, on the long-term, to an increase of an asymmetric scattering intensity distribution in −c-direction only. This distribution cannot be erased by white-light exposure, i.e. the underlying noisy refractive-index gratings are permanently fixed. Temperature-dependent measurements of the thermally activated decay of the gratings yield an activation energy of (0.97± 0.06) eV, which points to a contribution of charge-carriers with a low mobility, such as ions. The experimental procedure and the measured activation energy suggest an explaination via the effect of laser-induced local heating of the sample in combination with the well-known simultaneous thermal fixing procedure.

Financial support by the DFG (projects IM 37/2-2, GRK 695).