Nondegenerate two-photon absorption in GaAs/AlGaAs multiple quantum well waveguides

Abstract

We present femtosecond pump-probe measurements of the nondegenerate (1960-nm excitation and 1176–1326-nm probe) two-photon absorption spectra of 8-nm GaAs/12nmAl_{0.32}Ga_{0.68}As quantum well waveguides. Experiments were performed with light pulses copolarized normal and tangential to the quantum well plane. The results are compared to perturbative calculations of transition rates between states determined by the k·p method with an 8- or 14-band basis. We find excellent agreement between theory and experiment for normal polarization, then use the model to support predictions of orders-of-magnitude enhancement of nondegenerate two-photon absorption as one constituent photon energy nears an intersubband resonance.