It is shown that a three-band, nonparabolic, model for zinc-blende semiconductors provides a universal curve for the frequency dependence of the two-photon coefficient, whose magnitude differs between semiconductors by the factor ${\left(E_g{{}_{}{}^3{}_{}{}^{}n_p^{}{}_{}{}^{}}^2\right)}^{-1\mathrm{}}$. Good agreement is obtained with reported coefficients at 300°K for InSb, ${\mathrm{Hg}}_{1-x}{\mathrm{Cd}}_x\mathrm{Te}$, GaAs, and CdTe.

• Received 9 April 1979

DOI:https://doi.org/10.1103/PhysRevLett.42.1785