Limitation due to three-photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap

We report measurements of the spectral dispersion and the magnitude of three-photon absorption in Al0.18Ga0.82As for photon energies between one half and one third the band gap and show that a two-parabolic-band model is valid in this material. These results indicate that there is a limited spectral range below half the band gap in AlGaAs (and presumably all semiconductors) in which the bound electronic optical nonlinearity can be used without significant multiphoton absorption.