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Photoelectron Angular Distributions for Two-photon Ionization of Helium by Ultrashort Extreme Ultraviolet Free Electron Laser Pulses
- Publication Year :
- 2012
-
Abstract
- Phase-shift differences and amplitude ratios of the outgoing $s$ and $d$ continuum wave packets generated by two-photon ionization of helium atoms are determined from the photoelectron angular distributions obtained using velocity map imaging. Helium atoms are ionized with ultrashort extreme-ultraviolet free-electron laser pulses with a photon energy of 20.3, 21.3, 23.0, and 24.3 eV, produced by the SPring-8 Compact SASE Source test accelerator. The measured values of the phase-shift differences are distinct from scattering phase-shift differences when the photon energy is tuned to an excited level or Rydberg manifold. The difference stems from the competition between resonant and non-resonant paths in two-photon ionization by ultrashort pulses. Since the competition can be controlled in principle by the pulse shape, the present results illustrate a new way to tailor the continuum wave packet.<br />Comment: 5 pages, 1 table, 3 figures
- Subjects :
- Physics - Atomic Physics
Subjects
Details
- Database :
- arXiv
- Publication Type :
- Report
- Accession number :
- edsarx.1204.4812
- Document Type :
- Working Paper
- Full Text :
- https://doi.org/10.1088/0953-4075/46/16/164018