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DOE OSTI · 2588146

Nonresonant two-photon x-ray absorption in Cu

Kas, J. J. [Univ. of Washington, Seattle, WA (United States)]·Rehr, J. J. [Univ. of Washington, Seattle, WA (United States)] (ORCID:0000000244113125)·Stöhr, J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000158151918)·Vinson, J. [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)] (ORCID:0000000276197060)
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Abstract

We present a real-space Green's function theory and calculations of two-photon x-ray absorption (TPA). Our focus is on nonresonant 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 independent particle Green's function treatment of the Kramers-Heisenberg equation and an approximation for the sum over nonresonant 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. Furthermore, we also briefly discuss many-body corrections and TPA sum rules.

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Approximation methods for many-body systemsElectronic structureFirst-principles calculationsGreen's function methods

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Kas, J. J. [Univ. of Washington, Seattle, WA (United States)], Rehr, J. J. [Univ. of Washington, Seattle, WA (United States)] (ORCID:0000000244113125), Stöhr, J. [SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)] (ORCID:0000000158151918), Vinson, J. [National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)] (ORCID:0000000276197060). 2025-07-10. Nonresonant two-photon x-ray absorption in Cu. https://doi.org/10.1103/t8cn-d9yy

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Approximation methods for many-body systems↗