An optically controllable terahertz filter

Using a mixed type-I/type-II GaAs/AlAs multiple-quantum-well sample, we hav e demonstrated an optically controllable and tunable terahertz (THz) filter . Long-lived electron-hole pairs in the quantum wells allow for efficient T Hz attenuation over a large THz spot size (2 mm) for extremely low optical cw power. This sample can also be used as an optically tunable THz phase sh ifter. The optically induced change of the GaAs quantum wells from a dielec tric to a conducting material leads to the observed attenuation and the shi fting of the THz wave forms. (C) 2000 American Institute of Physics. [S0003 -6951(00)02920-X].