부산대학교 도서관

We have calculated, using second order perturbation theory, the two photon ionization cross section of a K-shell electron of chlorine forE=1.6 keV incident photons. Two classes of intermediate states must be considered, those in which a 1s electron moves to an emptyp-orbital, and those in which an electron from an occupiedp-orbital moves into the continuum. The first class of intermediate states is followed by the ejection of ap-electron into the continuum. The second class of intermediate states is followed by the transfer of a 1s electron into an emptyp-state. The largest contribution comes from 3p [right arrow]d-continuum followed by 1s [right arrow] 3p transition. Our result is [sigma].sup.(2)/I=2.06x10.sup.41 cm.sup.4/W where [sigma].sup.(2) is the two photon ionization cross-section andI is the light intensity.