Excited-state dynamics and nonlinear optical response of Ge nanocrystals embedded in silica matrix

We use a dedicated Z -scan setup, arranged to account for cumulative effects, to study the nonlinear optical response of Ge nanocrystals embedded in silica matrix. Samples are prepared with plasma-enchanced chemical-vapor deposition and post-thermal annealing. We measure a third-order nonlinear refraction coefficient of γ=1× 10-16 m2 W. The nonlinear absorption shows an intensity-independent coefficient of Β=4× 10-10 mW related to fast processes. In addition, we measure a second Β component around 10-9 mW with a relaxation time of 300 μs that rises linearly with the laser intensity. We associate its origin to the absorption of excited carriers from a surface-defect state with a long depopulation time. © 2006 American Institute of Physics