Competition between one- and two-photon processes in Ar irradiated by the Shanghai soft x-ray free electron laser
Shanghai Soft X-ray Free Electron Laser facility has entered user operation, delivering soft x-ray pulses in self-amplified spontaneous emission mode with an intensity of the peak fluence of ∼1.0×10^{−2}µJ/µm^{2} at a focus point. With these conditions, at a photon energy of 260 eV, we expect sequen...
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| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
American Physical Society
2025-08-01
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| Series: | Physical Review Research |
| Online Access: | http://doi.org/10.1103/j4rx-55m2 |
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| Summary: | Shanghai Soft X-ray Free Electron Laser facility has entered user operation, delivering soft x-ray pulses in self-amplified spontaneous emission mode with an intensity of the peak fluence of ∼1.0×10^{−2}µJ/µm^{2} at a focus point. With these conditions, at a photon energy of 260 eV, we expect sequential processes in which Ar^{2+} created by the Auger decay following the 2p photoionization may be resonantly excited to the 2p^{−1}3p^{−2}3d inner-shell excited state and thus resonant Auger decay produces Ar^{3+}, which can also be competitively produced by the direct double Auger decay (DDAD) following the one-photon 2p ionization of Ar. Ar^{4+} ions dominantly arise from Ar^{2+} with a resonant excitation and subsequent DDAD, involving two-photon absorption. The measured charge distributions as a function of the free-electron laser (FEL) fluence are well reproduced by ab initio calculations that include DDAD, normally neglected in the previous FEL studies, and resonant Auger decay. The present results demonstrate that the low peak fluence of the FEL pulses can be determined if the competition between the one- and two-photon processes is precisely described along with DDAD and resonant Auger decay. |
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| ISSN: | 2643-1564 |