Optical absorption in mesoscopic structures in intense THz-fields

We have theoretically studied the effect of THz radiation on the linear optical absorption spectra of semiconductor structures. A general theoretical framework, based on nonequilibrium Green functions, is formulated and applied to the calculation of linear optical absorption spectrum for several nonequilibrium mesoscopic structures. We show that a blue-shift occurs and sidebands appear in bulk-like structures (the dynamical Franz-Keldysh effect). The properties of the calculated side-band intensities and energies appear to resolve problems in the interpretation of data obtained with the Free Electron Laser at UCSB. An analytical calculation leads to the prediction that in the case of superlattices distinct stable steps appear in the absorption spectrum when conditions for dynamical localization are met.