First-principle study of two-photon absorption in FeO.

Utilizing the length gauge and the electron density operator, we calculate the two-photon absorption (2PA) coefficient of FeO based on a full ab initio band structure. The pure two-photon interband transitions and those modulated by intraband transitions have been separated explicitly to determine their impact on the 2PA spectrum. A single main absorption peak instead of two will present in the spectrum by including the hybridization of inter- and intra-band transitions, which can be identified easily in future experimental studies.