Complete bleaching of the intersubband absorption in GaAs/AlGaAs quantum wells using a far-infrared free-electron laser

Abstract
The intensity-dependent intersubband absorption in GaAs/AlGaAs quantum wells with a subband separation smaller than the optical phonon energy has been measured with a pulsed far-infrared free-electron laser. Complete bleaching of the absorption is observed at I=200 kW/cm2. Fitting the data with a two-level system yields a characteristic time constant of 1–2 ps. Possible interpretations, considering the finite pulse width of the laser, are discussed.