Dynamics of optical nonlinearity of Ge nanocrystals in a silica matrix
نویسندگان
چکیده
The optical nonlinearity and excited carrier lifetime in Ge nanocrystals (nc-Ge) embedded in a silica matrix have been investigated by means of single beam z scan and pump-probe techniques with laser pulse duration of 35 ps and 532 nm wavelength. The nc-Ge samples were prepared using magnetron cosputtering and postgrowth annealing at 800 °C. The nonlinear absorption coefficient a2 and refractive index n2 were found to range between 190 and 760 cm/GW, and 0.0026 and 0.0082 cm/GW, respectively, and be proportional to the Ge concentration in the film. The confined excited carriers were found to depopulate with a lifetime of ;70 ps. The nonlinearity in Ge nanocrystals is deduced to originate mainly from excited carrier absorption, with two-photon absorption providing a small contribution. © 2000 American Institute of Physics. @S0003-6951~00!05249-9#
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