Complete reconstruction of bound and unbound electronic wavefunctions in two-photon double ionization


To be complete, the characterization of the photoionization process of atoms and molecules requires the extraction of all quantum-mechanical phases and amplitudes. So far, complete experiments have accessed only the ionization process of neutral atoms and molecules. Here we report the quantum-mechanically complete characterization of the single and double ionization of neon to yield doubly charged ions. The first ionization step by intense, polarized extreme ultraviolet light from a free-electron laser leaves the ion in a polarized state (that is, one in which the angular momentum of the ion is aligned in space). By controlling the polarization of the light, we determine the bound and continuum components of the system in the first and second ionization steps leading to the formation of doubly charged neon ions. We test the validity of our approach by characterizing the influence of autoionizing ionic states on the two-photon double-ionization mechanism. Our results are important for understanding the physics of the interaction of extreme ultraviolet radiation with ions.

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Fig. 1: Energy-level diagram and photoelectron spectrum for the two-photon double ionization of neon.
Fig. 2: Two-photon double ionization of neon in the spectral range 44.0–62.0 eV.
Fig. 3: Two-photon double ionization of neon in the region of autoionizing states 2s2p53p.
Fig. 4: Complete experiment on photoionization of Ne+ 2p5 2P to the Ne2+ 2p4 3P state at the photon energy 53 eV.
Fig. 5: Complete experiment on photoionization of Ne+ 2p5 2P to the Ne2+ 2p4 3P state at the photon energies close to the region of autoionizing resonances.
Fig. 6: Reconstruction of bound and unbound electronic density distributions.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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Financial support by the Italian Ministry of Research (project FIRB no. RBID08CRXK) is gratefully acknowledged. This project has also received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 641789 MEDEA. D.F and M.N. acknowledge support from the European Research Council Starting Research Grant UDYNI (grant agreement no. 307964). K.U. acknowledges support by the X-ray Free Electron Laser Utilization Research Project and the X-ray Free Electron Laser Priority Strategy Program of the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), by the Cooperative Research Program of ‘Network Joint Research Center for Materials and Devices: Dynamic Alliance for Open Innovation Bridging Human, Environment and Materials’, by the bilateral project CNR-JSPS ‘Ultrafast science with extreme ultraviolet Free Electron Lasers’ and by the IMRAM project for the international co-operation. M.M. acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) under grant no. SFB 925.

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K.U., G.S. and A.N.G.-G. conceived the present study. M.R., D.F., M.N., K.U., F.F., F.S., Y.O., M.M., O.P., P.F., K.C.P., C.C. and G.S. conducted the experiment. P.A.C. analysed the experimental data. A.D. contributed to the development of the analysis programmes. E.V.G., S.M.B. and A.N.G.-G. developed the theoretical background and performed the numerical simulations. E.V.G., A.N.G.-G. and G.S. drafted the manuscript. All authors discussed the experimental results and the final version of the manuscript.

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Correspondence to A. N. Grum-Grzhimailo or G. Sansone.

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Carpeggiani, P.A., Gryzlova, E.V., Reduzzi, M. et al. Complete reconstruction of bound and unbound electronic wavefunctions in two-photon double ionization. Nature Phys 15, 170–177 (2019).

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