Excitonic optical absorption in semiconductors under intense terahertz radiation

The excitonic optical absorption of GaAs bulk semiconductors underintense terahertz (THz) radiation is investigated numerically. Themethod of solving initial-value problems, combined with the perfectmatched layer technique, is used to calculate the opticalsusceptibility. In the presence of a driving THz field, in additionto the usual exciton peaks, 2p replica of the dark 2p exciton andeven-THz-photon-sidebands of the main exciton resonance emerge inthe continuum above the band edge and below the main excitonresonance. Moreover, to understand the shift of the position of themain exciton peak under intense THz radiation, it is necessary totake into consideration both the dynamical Franz--Keldysh effect andac Stark effect simultaneously. For moderate frequency fields, themain exciton peak decreases and broadens due to the field-inducedionization of the excitons with THz field increasing. However, forhigh frequency THz fields, the characteristics of the exciton recureven under very strong THz fields, which accords with the recentexperimental results qualitatively.