Dispersion of phonon-assisted nonresonant third-order nonlinearities
01 November 2003
An analysis of the dispersion of two-photon absorption and Kerr nonlinearity of indirect semi-conductors below the indirect bandgap is presented. Similar to the case of the linear absorption, third-order nonlinear processes are found to be mediated by phonon-assisted transitions.
The re-sulting Kerr coefficient n2 is positive below the indirect gap, and the dispersion of the third-order nonlinearities is reduced relative to direct semiconductors. The results are compared with exist-ing experimental data in silicon.