Two-photon absorption spectroscopy in GaAs quantum wells

Two-photon absorption spectroscopy was performed in GaAs quantum wells with photon energy ħω near half the band gap ${\mathrm{E}}_{\mathrm{g}}$. For the case of incident light polarized perpendicular to the confinement direction ε^⊥z^, the onset of two-photon absorption occurs at the 2P state of the lowest-energy heavy-hole exciton and the absorption increases linearly with 2ħω-${\mathrm{E}}_{\mathrm{g}}$. For ε^∥z^, the two-photon spectrum is stepped with superpositions of sharp 1S exciton features at odd ΔN light-hole–conduction-band transitions. These results are used to accurately determine exciton binding energy, successive subband energy splittings, and band offsets.