标题： 非共振双光子X射线吸收在铜中 显示英文标题

标题： Non-resonant two-photon x-ray absorption in Cu

摘要： 我们提出了一种实空间格林函数理论和双光子X射线吸收（TPA）的计算。 我们的重点是金属铜中的非共振K壳层TPA，这已在强X射线自由电子激光（XFEL）源中被实验观察到。 该理论基于Kramers-Heisenberg方程的独立粒子格林函数处理，以及对非共振中间态求和的一种近似，该近似用静态四极矩跃迁算符表示。 XFEL效应通过部分耗尽的d带进行建模。 这种方法被证明在定量上与XFEL实验和Bethe-Salpeter方程方法的结果一致。 我们还简要讨论了多体修正和TPA求和规则。 显示英文摘要

摘要： We present a real-space Green's function theory and calculations of two-photon x-ray absorption (TPA). Our focus is on non-resonant K-shell TPA in metallic Cu, which has been observed experimentally at intense x-ray free electron laser (XFEL) sources. The theory is based on an independentparticle Green's function treatment of the Kramers-Heisenberg equation and an approximation for the sum over non-resonant intermediate states in terms of a static quadrupole transition operator. XFEL effects are modeled by a partially depleted d-band. This approach is shown to give results for K-shell TPA in quantitative agreement with XFEL experiment and with a Bethe-Salpeter Equation approach. We also briefly discuss many-body corrections and TPA sum-rules.