Intersubband stimulated emission in GaAs/AlGaAs quantum wells: Pump-probe experiments using a two-color free-electron laser

Intersubband stimulated emission under optical pumping has been observed in the conduction band of GaAs-AlGaAs quantum wells. The asymmetric coupled quantum wells which exhibit three conduction bound levels are designed to exhibit population inversion under optical pumping. An optical excitation at lambda = 9.2 mu m is used to bleach the absorption between the ground and second excited subband. The population inversion between excited subbands is pumped and probed on a picosecond time scale by a tunable two-color free-electron laser. The stimulated amplification is studied at low temperature in infrared waveguides as a function of the waveguide length and of the probe wavelength. A stimulated gain approximate to 80 cm(-1) is measured at 12.5 mu m in agreement with calculations. (C) 1997 American Institute of Physics.