The non-local nature of free-carrier nonlinearity : theory and novel applications

Orateur : Yonatan SIVAN (Ben Gurion University)

One of the most fundamental nonlinear optical effects is the change of the refractive index of the material induced by light propagating in it. This effect is used in countless applications, most prominently, in modulations of semiconductor-based electro-optic components. Thes e modulations are most frequently based on changing the free charge-carrier density. In this case, the modulation speed is limited by the natural pico-second to nano-second carrier recombination times. However, femto-second modulation times are required for many technological applications as well as for the study of various fundamental physics problems. Conventional approaches for shortening the carrier lifetime rely on material-science-based modifications of the material platform. In this talk I will introduce a different approach, based on novel ideas from wave physics, and on an aspect of the nonlinear response of free-carrier which was so far ignored – carrier diffusion, or the non-local nature of the free-carrier nonlinearity. We show that this effect becomes dominant when the spatial distribution of the free-carrier has nano-scale features, e.g., in the case of transient Bragg gratings. Based on this phenomenon, I will show how we can easily achieve sub-picosecond switching times in semiconductors and metals, how to time-reverse short pulses, and most importantly, how to use this configuration to generate short pulses of arbitrary wavelength and duration via a phenomenon we coin as spectral inheritance. I will provide intuitive explanations to these phenomena, but also review the complex analysis and numerics associated with this unusual regime of pulsed wave interactions and give a glimpse into the non-equilibrium dynamics of the hot charge-carriers.

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