Dispersion of the two-photon absorption coefficient in ZnSe

The dispersion of the degenerate two-photon absorption coefficient is measured in ZnSe in the energy region from 2.66 to 3.52 eV, corresponding to 0.5<hν/Eg<0.66. Our results clearly show the sizeable contribution of the split-off band to the strength of the nonlinear absorption. By contrasting our measurement with several theoretical calculations, we find that at least the lowest four-bands should be included in the band-structure model of the two-photon absorption. General scaling laws for the calculation of the two-photon absorption coefficient provide a good estimate of the strength of the absorption but fail to account for details of the spectrum.