Investigation of mid-infrared intersubband stimulated gain under optical pumping in GaAS/AlGaAs quantum wells

We have investigated the mid-infrared intersubband stimulated emission under optical pumping in GaAs/AlGaAs coupled quantum wells. The quantum wells exhibit four levels bound in the conduction band. The energy between the ground and first excited subband is close to the optical phonon energy enabling population inversion. Intersubband stimulated gain between subbands E-3 and E-2 is observed around 14 mu m wavelength by optically pumping the E-1-E-3 intersubband transition at 10 mu m. The gain measurement is performed by time-resolved pump-probe experiments using a two-color picosecond free-electron laser. The dependence of the intersubband stimulated emission is analyzed as a function of the pump intensity, and the pump and probe wavelengths. We show that very large intersubband stimulated gain can be achieved at liquid nitrogen temperature in a 2 mm thick waveguide. The stimulated gain is resonant with the pump wavelength with a broadening approximate to 25 meV. The experimental results are explained with a nonperturbative matrix density treatment of a three-level system. (C) 1998 American Institute of Physics.