2-COLOR MIDINFRARED SATURATION SPECTROSCOPY OF INTERSUBBAND TRANSITIONS IN MULTIQUANTUM WELLS

A two-color pump-probe study of bound-to-bound and bound-to-quasibound intersubband transitions in InGaAs/AlGaAs and GaAs/AlGaAs multiquantu m wells (MQW), with transition energies near 250 meV has been performe d. Electrons were optically excited from the lowest to the upper subba nd using short midinfrared pulses of intensities up to 10(8) W/cm(2) f rom a dual optical parametric generator. Differential transmission spe ctra, taken with the weaker probe pulses, evidence homogeneous line br oadening behavior. From the width of the coherence peak, centered near the pump frequency, and arising from a dynamic population grating, th e upper state lifetime (bound-to-bound transition) was found to be 0.6 ps, in good quantitative agreement with absorption saturation data. ( C) 1996 American Institute of Physics.