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A: Atomphysik
A 18: Multiphotonionisation II
A 18.1: Talk
Thursday, March 25, 2004, 16:30–16:45, HS 133
Photoionization of helium atoms irradiated with intense VUV free-electron laser light: Multiphoton versus single photon processes — •T. Laarmann1,2, H. Wabnitz1, J. Schulz1, P. Gürtler1, W. Laasch1, A. R. B. de Castro3, and T. Möller1 — 1HASYLAB at DESY, Notkestr. 85, 22603 Hamburg, Germany — 2Max Born Institute, Max-Born-Str. 2a, 12489 Berlin, Germany — 3LNLS 13084-971 Campinas SP, Brazil
With the discovery of above-threshold ionization (ATI) in 1979 [1], tremendous efforts both experimentally and theoretically have begun to investigate highly non-linear phenomena in rare gas atoms irradiated with intense optical fs-laser pulses. Very recently, the free-electron laser (FEL) at DESY has opened the door to a new regime of strong-field matter interaction in the vacuum-ultraviolet (VUV) [2]. This contribution reports on time-of-flight mass and photoelectron spectroscopy of He atoms irradiated with 100 fs FEL pulses at 95 nm (∼13 eV). At peak intensities of 1010−1013 W/cm2, ionization of He is observed which is due to both, non-linear multiphoton ionization with the fundamental and single-photon ionization with 3rd harmonic radiation. The experimentally observed photoemission lines will be discussed in the context of a theoretically predicted 3-photon ionization peak (ATI) and ionization processes due to 3rd harmonic FEL light.
[1] P. Agostini et al., Phys. Rev. Lett. 42, 1127 (1979)
[2] H. Wabnitz et al., Nature 420, 482 (2002)