Bound electronic and free carrier nonlinearities in Silicon nanocrystals at 1550nm

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Abstract
We present a detailed investigation of the different processes responsible for the optical nonlinearities of silicon nanocrystals at 1550 nm. Through z-scan measurements, the bound-electronic and excited carrier contributions to the nonlinear refraction were measured in presence of two-photon absorption. A study of the nonlinear response at different excitation powers has permitted to determine the change in the refractive index per unit of photo-excited carrier density σr and the value of the real bound-electronic nonlinear refraction n2be as a function of the nanocrystals size. Moreover at high excitation power, a saturation of the nonlinear absorption was observed due to band-filling effects.