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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.