NONLINEAR INTERSUBBAND ABSORPTION OF A HOT QUASI-2-DIMENSIONAL ELECTRON-PLASMA STUDIED BY FEMTOSECOND INFRARED-SPECTROSCOPY

The transient (n=1) to (n=2) intersubband absorption of a pure electro n plasma in n-type Ga0.48In0.53As/Al0.48In0.52As quantum wells is stud ied in femtosecond pump-probe experiments. The ultrafast dynamics of n onlinear absorption shows strong changes when tuning the midinfrared p ulses over the intersubband absorption line. The nonlinear optical res ponse is determinedby both intersubband relaxation with a time constan t of 1.3 ps and the intraband dynamics of (n=1) electrons, which are m onitored in an independent experiment.