Transient four-wave mixing on (InGa)As/InP multiple quantum wells using a femtosecond optical parametric oscillator

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Abstract
We present femtosecond four-wave mixing (FWM) experiments on unstrained, thin (InGa)As/InP multiple quantum wells in the spectral region around 1175 nm. These experiments became feasible by employing a stabilized femtosecond optical parametric oscillator which generates tunable 160 fs pulses in the near-infrared. The dephasing time of the heavy-hole exciton is determined to be 1.2 ps at low temperature, corresponding to a homogeneous linewidth of 1.1 meV. In addition, a beating of the FWM signal with a time period of 1.3 ps corresponding to an energy spacing of 3.2 meV is observed. We attribute this to the simultaneous excitation of localized excitons and excitons bound to an impurity or defect, which are not spectrally resolved in the linear optical spectra due to considerable inhomogeneous broadening.