Im{Chi((3))} Spectra Of 110-Cut Gaas, Gap, And Si Near The Two-Photon Absorption Band Edge

Spectra of the degenerate two-photon absorption coefficient beta(omega), anisotropy parameter sigma(omega), and dichroism parameter delta(omega) = [sigma(omega + 2 eta(omega)]/2 of crystalline 110-cut GaAs, GaP, and Si, at 300 K were measured using femtosecond pump-probe modulation spectroscopy over an excitation range in the vicinity of each material's half-bandgap E-g/2 (overall < 0.62 < (h) over bar omega, 1.91 eV or 2000 > lambda > 650 nm). Together, these three parameters completely characterize the three independent components of the imaginary part of the degenerate third-order nonlinear optical susceptibility tensor Im{chi((3))(abcd)(omega)}. In direct-gap GaAs, these components peak at (h) over bar omega approximate to 0.78 E-g, which is close to the peak at (h) over bar omega = 0.71 E-g predicted by the Jones-Reiss phenomenological model. The dispersion is comparable with ab initio calculations. In indirect-gap GaP and Si, these components tend to increase with (h) over bar omega over our tuning range. In Si, the dispersion differs significantly from predictions of semi-empirical models, and ab initio calculations do not account for transitions below the twophoton direct bandgap, motivating further investigation. Kleinman symmetry was observed to be broken in all three materials. We also note anomalies observed and their possible origins, emphasizing the advantages of a 2-beam experiment in identifying the contribution of various nonlinear effects.