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- Zitnik, M, et al.
(author)
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High resolution multiphoton spectroscopy by a tunable free-electron-laser light.
- 2014
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:19
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Journal article (peer-reviewed)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.
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