Energy band-gap dependence of two-photon absorption

We present measurements of the two-photon absorption coefficients β2 of 10 different semiconductors having band-gap energies between 1.4 and 3.7 eV. We find that β2 varies as Eg−3, as predicted by theory. In addition, the absolute values of β2 agree with theory, which includes the effect of nonparabolic bands, the average difference being less than 26%. This agreement permits confident predictions of two-photon absorption coefficients of other materials at other wavelengths.