ULTRAFAST DYNAMICS OF NONLINEAR INTERSUBBAND ABSORPTION IN N-TYPE MODULATION-DOPED GAINAS ALINAS QUANTUM-WELLS/

Tile nonlinear intersubband absorption of a quasi-two-dimensional elec tron plasma in n-type modulation doped Ga0.47In0.53As/Al0.48In0.52As m ultiple quantum wells is investigated by femtosecond pump-probe measur ements in the mid-infrared. We observe a strong dependence of the tran sient nonlinear intersubband absorption on the spectral position of th e pulses within the intersubband absorption line. The time-resolved me asurements demonstrate that the absorption dynamics is determined not only by intersubband relaxation with a time constant of 1.3 ps but als o by the intrasubband thermalization and subsequent cooling of the n = 1 electron distribution.