Optical saturation of intersubband absorption in GaAs-AlxGa1−xAs quantum wells

Abstract

We have investigated intersubband absorptions between the conduction ground state and the first excited state of two Al_xGa_1−xAs/GaAs/Al_xGa_1−xAs multiple quantum well structures with x=0.3 and 85 Å well width, and with x=0.57 and 96 Å well width. Small‐signal measurements show absorption peaks at 10.45 and 10.15 μm, respectively. Under an intense resonant excitation from a pulsed CO₂ laser, saturation of the intersubband absorption occurred. The saturation intensity is estimated to be 340±120 kW/cm² for the first sample and 375±120 kW/cm² for the second. From these values, we have deduced subband decay times of the order of 10.6±3.5 ps for the first sample and 15.5±5 ps for the second.