Optical transitions involving impurities in semiconductors under additional infrared laser radiation

The influence of an intense infrared (IR) laser field on the optical absorption edge associated to acceptor impurities of a direct-gap semiconductor is discussed. It is shown that as the IR laser field intensity increases the absorption coefficient is modified so as to give rise to an absorption tail below the free-field forbidden gap. An application is made for the case of the GaAs irradiated by an intense CO2 laser.