Application of Green’s-function technique to the calculation of multiphoton absorption coefficients of crystalline solids

The Green’s-function method is introduced to avoid the sums over intermediate states occurring in the calculation of multiphoton absorption coefficients of crystalline solids. Up to four-photon absorption coefficients of NaCl are obtained by this method. The results are in accord with those obtained by carrying out the summations directly. The advantages of the method and its further applications are also discussed in the paper.