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Phase-resolved attosecond near-threshold photoionization of molecular nitrogen

2009; American Physical Society; Volume: 80; Issue: 1 Linguagem: Inglês

10.1103/physreva.80.011404

1538-4446

Stefan Haessler, B. Fabre, J. Higuet, Jérémie Caillat, Thierry Ruchon, P. Breger, B. Carré, E. Constant, A. Maquet, E. Mével, P. Salières, Richard Taïeb, Y. Mairesse,

Spectroscopy and Quantum Chemical Studies

We photoionize nitrogen molecules with a train of extreme ultraviolet attosecond pulses together with a weak infrared field. We measure the phase of the two-color two-photon ionization transition (molecular phase) for different states of the ion. We observe a $0.9\ensuremath{\pi}$ shift for the electrons produced in the ionization channels leading to the $X\text{ }{^{2}\ensuremath{\Sigma}}_{g}^{+}$, ${v}^{\ensuremath{'}}=1$, and ${v}^{\ensuremath{'}}=2$ states. We relate this phase shift to the presence of a complex resonance in the continuum. By providing both a high spectral and temporal resolution, this general approach gives access to the evolution of extremely short-lived states, which is often not accessible otherwise.