Attosecond-Resolved Evolution of a Laser-Dressed Helium Atom: Interfering Excitation Paths and Quantum Phases

Niranjan Shivaram, Henry Timmers, Xiao-Min Tong, and Arvinder Sandhu
Phys. Rev. Lett. 108, 193002 – Published 9 May 2012

Abstract

Using high-order harmonic attosecond pulse trains, we investigate the photoionization dynamics and transient electronic structure of a helium atom in the presence of moderately strong (1012Wcm2) femtosecond laser pulses. We observe quantum interferences between photoexcitation paths from the ground state to different laser-dressed Floquet state components. As the intensity ramps on femtosecond time scales, we observe switching between ionization channels mediated by different atomic resonances. Using precision measurements of ion yields and photoelectron distributions, the quantum phase difference between interfering paths is extracted for each ionization channel and compared with simulations. Our results elucidate photoionization mechanisms in strong fields and open the doors for photoabsorption or photoionization control schemes.

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  • Received 31 July 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.193002

© 2012 American Physical Society

Authors & Affiliations

Niranjan Shivaram1,*, Henry Timmers1, Xiao-Min Tong2, and Arvinder Sandhu1,†

  • 1Department of Physics, University of Arizona, Tucson, Arizona 85721, USA
  • 2Center for Computational Sciences, University of Tsukuba, Ibaraki 305-8573, Japan

  • *niranjan@physics.arizona.edu
  • sandhu@physics.arizona.edu

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Vol. 108, Iss. 19 — 11 May 2012

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