First demonstration of room temperature intersubband-interbanddouble-resonance spectroscopy of GaAs/AlGaAs quantum wells

Intersubband-interband double-resonance experiments in undoped GaAs/Al_0.33Ga_0.67As multiple quantum well (MQW) structures at room temperature are discussed. The well width is 78 Å. A Ti:sapphire laser is used to pump the interband transitions, while the first intersubband transition is probed with a CO₂ laser. The intersubband absorption is found to peak at 10.6 μm, and a 10-meV linewidth is measured. The absorption signal is also recorded at a fixed CO₂ tuning while varying the pump laser wavelength from 700 to 850 nm. A high-resolution spectrum is obtained, reflecting the steplike density of states with sharp peaks at the exciton resonances