TERAHERTZ DYNAMICS IN CONFINED MAGNETOEXCITONS

We have investigated the linear and nonlinear response of confined mag netoexcitons to intense terahertz (THz) radiation. By monitoring photo luminescence from THz-driven GaAs quantum wells, we have observed for the first time internal transitions in direct excitons. The spectrum o f excitations is enriched by the complexities of the valence band and is well explained by an effective-mass theory. At high THz-field stren gths, the emission properties of the driven quantum wells are complete ly dominated by new near-band-gap features, or optical sidebands, whic h appear at frequencies omega(NIR) +/- 2n omega(THz), where omega(NIR) is the exciton-creation frequency, omega(THz) is the driving frequenc y, and n is an integer. The intensity of the sidebands exhibits pronou nced enhancement when omega(THz) coincides with one- and two-photon ex citon internal transitions, providing new and accurate information on the internal dynamics of excitons. (C) 1998 Elsevier Science B.V. All rights reserved.