Nonlinear reflection of medium-infrared light from a structure containing highly doped GaAs layers

The optical non-linearity based on the non-parabolicity and the intervalley transfer in highly doped n-GaAs has been proposed. A large fraction of the light mass central valley population can be effectively transferred to the heavy mass satellite valleys by optically heating the free carriers with CO2 laser light, leading to a non-linear refractive index n2 of the order of 10-8 cm2/W. Integrating such non-linear layers in a suitable interferometer drastically decreases the non-linear threshold value. Together with the intrinsically small intravalley and intervalley relaxation times (picosecond time scale), this optical heating effect can be used as a versatile tool for improving our understanding of carrier- lattice interactions and hot electron effects in highly doped semiconductors as well as an optical spectroscopic probe for investigating other ultrafast physical, chemical, or biological processes. By introducing feed-back mechanisms, all-optical clocks and delay lines could be conceived with response times of the order of a few ps.