TERAHERTZ DYNAMICS OF EXCITONS IN GAAS ALGAAS QUANTUM-WELLS/

By monitoring changes in excitonic photoluminescence that are induced by far-infrared (FIR) radiation, we observed resonant FIR absorption b y magnetoexcitons in GaAs/AlGaAs quantum wells. The dominant resonance is assigned to the 1s --> 2p(+) transition of the heavy-hole exciton, and agrees well with theory. At low FIR and interband excitation inte nsities, the 1s --> 2p(+) absorption feature is very narrow and broade ns as either of these intensities is increased. The 1s --> 2p(+) absor ption feature persists even when the FIR electric field is comparable to the electric field which binds the exciton.