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Science 5 December 2008:
Vol. 322. no. 5907, pp. 1525 - 1529
DOI: 10.1126/science.1163439
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Reports

Attosecond Ionization and Tunneling Delay Time Measurements in Helium

P. Eckle,1 A. N. Pfeiffer,1 C. Cirelli,1 A. Staudte,2 R. Dörner,3 H. G. Muller,4 M. Büttiker,5 U. Keller1

It is well established that electrons can escape from atoms through tunneling under the influence of strong laser fields, but the timing of the process has been controversial and far too rapid to probe in detail. We used attosecond angular streaking to place an upper limit of 34 attoseconds and an intensity-averaged upper limit of 12 attoseconds on the tunneling delay time in strong field ionization of a helium atom. The ionization field derives from 5.5-femtosecond-long near-infrared laser pulses with peak intensities ranging from 2.3 x 1014 to 3.5 x 1014 watts per square centimeter (corresponding to a Keldysh parameter variation from 1.45 to 1.17, associated with the onset of efficient tunneling). The technique relies on establishing an absolute reference point in the laboratory frame by elliptical polarization of the laser pulse, from which field-induced momentum shifts of the emergent electron can be assigned to a temporal delay on the basis of the known oscillation of the field vector.

1 Physics Department, Eidgenössische Technische Hochschule (ETH) Zürich, CH-8093 Zürich, Switzerland.
2 Steacie Institute for Molecular Sciences, National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario K1A 0R6, Canada.
3 Institut für Kernphysik, Johann Wolfgang Goethe Universität, Max-von-Laue-Straße 1, 60438 Frankfurt am Main, Germany.
4 Stichting voor Fundamenteel Onderzoek der Materie–Institute for Atomic and Molecular Physics, Kruislaan 407, 1098 SJ Amsterdam, Netherlands.
5 Physics Department, University of Geneva, CH-1211 Geneva, Switzerland.

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
Laser Tunnel Ionization from Multiple Orbitals in HCl.
H. Akagi, T. Otobe, A. Staudte, A. Shiner, F. Turner, R. Dorner, D. M. Villeneuve, and P. B. Corkum (2009)
Science 325, 1364-1367
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