Optical absorption of THz-field-driven and dc-biased quantum wells

Linear optical absorption in a quantum well driven by a growth-direction-oriented THz electric field is investigated. We show that if in addition to the THz field a dc bias field is applied to the quantum well, the optical absorption becomes much more sensitive to the presence of the THz field. This results in the emergence of multiple replicas in the absorption spectrum of biased quantum wells for a low-frequency (compared with the subband energy spacing) THz field. We consider undoped quantum wells and develop an approach that allows us to treat nonlinear effects in THz field strength. We discuss separately the optical absorption due to free-electron-hole pairs and due to excitons.