Optical Stark Shift in Quantum Wells

Abstract

Excitonic resonances are at the origin of large optical nonlineari-ties, especially in Multiple Quantum Well Structures (MQWS) where moreover they are present even at room temperature. These features make MQWS very attractive both from a fundamental point of view and for applications to optical devices. The recently reported optical Stark effect^1,2,3,4 has raised a wide current of interest since it corresponds to the coupling of electronic states with photons of energy below the absorption edge. The use of a pump wavelength in the transparency region of the MQWS offers great promise for optical devices since it implies an ultrafast response time and almost the absence of heat dissipation. It was already known for atoms that the virtual absorption and re-emission of non-resonant photons leads to a shift of the atomic levels. In solids such a situation is also encountered for transitions like excitons. The small magnitude of the corresponding energy shift with respect to typical excitonic transitions linewidth requires the use of lasers with quite high peak power. This is obtained by using very short laser pulses (10⁻¹³ s) which in the same time provide direct information on the dynamics of this optical Stark effect(OSE).