Photoluminescence from ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells quenched by intense far-infrared radiation

We present an experimental study of the effects of intense far-infrared (FIR) radiation on the excitonic photoluminescence (PL) from ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs quantum wells. The FIR electric field was polarized parallel to the plane of undoped, 100-Å-wide ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As/GaAs wells. Electron-hole pairs, created by relatively weak visible pulses, were excited by FIR pulses with intensities of up to 70 kW/${\mathrm{cm}}^2$ at frequencies of 29.5 and 43.3 ${\mathrm{cm}}^{\mathrm{-}1}$ (3.7 and 5.4 meV). Both quenching and broadening of free-exciton PL peaks were observed for rms FIR field strengths above a threshold of order 100 V/cm.