Quasienergy spectroscopy of excitons

We theoretically study nonlinear optics of excitons under intense THz irrad iation. In particular, the linear near-infrared absorption and resonantly e nhanced nonlinear sideband generation are described. We predict a rich stru cture in the spectra which an be interpreted in terms of the quasienergy sp ectrum of the exciton, via a remarkably transparent expression for the susc eptibility, and show that the effects of strongly avoided quasienergy cross ings manifest themselves directly, both in the absorption and transmitted s idebands.