TIME-DOMAIN MEASUREMENT OF INTERSUBBAND OSCILLATIONS IN A QUANTUM-WELL

We report time-domain measurements of electron intersubband oscillatio ns in quantum wells. We use an interferometric technique to measure th e change in the profile of a few-cycle THz pulse due to propagation th rough a modulation-doped Al0.3Ga0.7As/GaAs multiple quantum well struc ture (10x510 Angstrom wells). From this data we obtain the absorption and the index of refraction due to electrons in the quantum well, and due to the GaAs substrate, Unlike existing studies of coherent charge oscillations of electrons and holes in heterostructures excited by ult rashort pulses of band-gap light, our all-THz measurements quantitativ ely determine the linear optical properties of the quantum well electr ons. (C) 1998 American Institute of Physics.