High resolution multiphoton spectroscopy by a tunable free-electron-laser light

M Žitnik; A Mihelič; K Bučar; M Kavčič; J-E Rubensson; M Svanquist; J Söderström; R Feifel; C Såthe; Y Ovcharenko; V Lyamayev; T Mazza; M Meyer; M Simon; L Journel; J Lüning; O Plekan; M Coreno; M Devetta; M Di Fraia; P Finetti; R Richter; C Grazioli; K C Prince; C Callegari

doi:10.1103/PhysRevLett.113.193201

High resolution multiphoton spectroscopy by a tunable free-electron-laser light

Phys Rev Lett. 2014 Nov 7;113(19):193201. doi: 10.1103/PhysRevLett.113.193201. Epub 2014 Nov 7.

Authors

M Žitnik¹, A Mihelič², K Bučar², M Kavčič², J-E Rubensson³, M Svanquist³, J Söderström³, R Feifel⁴, C Såthe⁵, Y Ovcharenko⁶, V Lyamayev⁷, T Mazza⁸, M Meyer⁸, M Simon⁹, L Journel⁹, J Lüning⁹, O Plekan¹⁰, M Coreno¹⁰, M Devetta¹⁰, M Di Fraia¹¹, P Finetti¹⁰, R Richter¹⁰, C Grazioli¹⁰, K C Prince¹², C Callegari¹⁰

Affiliations

¹ Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia.
² Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia.
³ Uppsala University, Department of Physics and Astronomy, P.O. Box 530, S-75121 Uppsala, Sweden.
⁴ Uppsala University, Department of Physics and Astronomy, P.O. Box 530, S-75121 Uppsala, Sweden and University of Gothenburg, Department of Physics, SE-412 96 Gothenburg, Sweden.
⁵ MAX IV Laboratory, Lund University, P.O. Box 118, 22100 Lund, Sweden.
⁶ Technische Universität Berlin, Institut für Optik und Atomare Physik, Eugene-Wigner-Building Hardenbergstrasse 36, D-10623 Berlin, Germany.
⁷ Institute of Physics, University of Freiburg, Hermann-Herder Strasse 3a, D-79104 Freiburg, Germany.
⁸ European XFEL GmbH, Albert-Einstein-Ring 19, 22761 Hamburg, Germany.
⁹ Sorbonne Université, UPMC Univ Paris 06, UMR 7614, LCPMR, 75005 Paris, France and CNRS, UMR 7614, LCPMR, 75005 Paris, France.
¹⁰ Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, I-34149 Basovizza, Trieste, Italy.
¹¹ Department of Physics, University of Trieste, Via Valerio 2, I-34124 Trieste, Italy.
¹² Elettra-Sincrotrone Trieste, Strada Statale 14-km 163, 5, I-34149 Basovizza, Trieste, Italy and eChemistry Laboratory, Faculty of Life and Social Sciences, Swinburne University of Technology, Hawthorn, Melbourne, Victoria 3122, Australia.

PMID: 25415905
DOI: 10.1103/PhysRevLett.113.193201

Abstract

Seeded free electron lasers theoretically have the intensity, tunability, and resolution required for multiphoton spectroscopy of atomic and molecular species. Using the seeded free electron laser FERMI and a novel detection scheme, we have revealed the two-photon excitation spectra of dipole-forbidden doubly excited states in helium. The spectral profiles of the lowest (-1,0)(+1) (1)S(e) and (0,1)(0) (1)D(e) resonances display energy shifts in the meV range that depend on the pulse intensity. The results are explained by an effective two-level model based on calculated Rabi frequencies and decay rates.