Berlin 2008 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 2: Electric, electromechanical and optical properties I
DF 2.8: Vortrag
Montag, 25. Februar 2008, 12:40–13:00, EB 107
Dynamics of optical degradation on LiB3O5-crystal surfaces during SFG — •Stefan Möller, Änne Andresen, and Mirco Imlau — Department of Physics, University of Osnabrück, D-49069 Osnabrück
We have investigated the phenomenon of optical degradation of LiB3O5 single crystal surfaces during sum-frequency generation (SFG) of UV-light (λ = 355 nm) by a focused Q-switched Nd:YAG laser (f = 20 kHz, τ1064 = 10 ns, P1064 = 1.5 W). The investigations were performed on timescales > 100 h and UV-intensities below the light induced damage threshold of the crystals. The degradations were studied with optical and analytical methods.
As a result we found a steady deposition of foreign material on the output crystal surface in the illuminated area. Here, XPS uncovered several foreign elements as Na, S, Si, Ca, C beside B and O depending on the composition of the ambient atmosphere during SFG. The temporal development of the degradation could be observed by measuring the beam profile behind the crystal. The beam divergence increased as a function of the deposition height, which led to a complex intensity profile in the far-field. Further illuminating lead to a catastrophic break-down of the surface and the beam profile. This is due to thermal damage originating from the UV-absorption of the deposited material. Three models for the deposition process are discussed: a) diffusion out of the LiB3O5-subsurface, b) deposition of atoms of the ambient atmosphere, c) chemical reactions of LiB3O5, water, and boric acid. Financial support by the DFG (TFB 13, project A5/13-04).