Time resolved intersubband optical transitions in optically pumped semi conductor lasers

Summary form only given. We use visible-infrared dual beam time-resolved spectroscopy to study the dynamics of carriers in optically pumped laser devices containing quantum heterostructures within their active layers. By tuning the probe energy through the intersubband absorption resonance, we directly measure the electron population in various momentum states within the first conduction subband of the lasing device. We use, for the first time, time-resolved intersubband absorption to directly probe the dynamics of the excited electronic plasma. We study GaAs/AlGaAs semiconductor quantum well (QW) lasers at various excitation densities, below and above their lasing threshold. The excitation, by an above bandgap, spectrally tunable, picosecond optical laser pump pulse, is followed by a mid-IR picosecond probe pulse, spectrally tuned to the QW intersubband optical transition resonance. By changing the delay time between the pump and the probe pulses, we investigate the temporal evolution of the photoexcited electrons before, during and after the lasing action.