Abstract
Time-resolved anisotropy parameters and cross-section ratios of the positive and negative sidebands from two-colour two-photon above threshold ionization of helium atoms are measured using photoelectron velocity map imaging with the selected 19th high-order harmonic at 29.1 eV in an 810 nm perturbative dressing field. The intensities of both the sidebands and the single-photon ionization depletion follow a Gaussian correlation function where the photoelectron angular distributions and cross-section ratios of the sidebands do not change as a function of the temporal delay between the extreme ultraviolet and infrared pulses. The experimental results are compared with theoretical predictions using the soft-photon approximation, showing poor agreement, and analytical expressions are derived using second-order perturbation theory to determine the relative magnitudes of the resulting S and D partial waves of the above threshold ionization features.
Original language | English |
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Pages (from-to) | 1241-1251 |
Number of pages | 11 |
Journal | Molecular Physics |
Volume | 108 |
Issue number | 7-9 |
DOIs | |
State | Published - Oct 2010 |
Externally published | Yes |
Funding
The authors would like to thank Daniel Strasser for many helpful discussions. The authors gratefully acknowledge financial support by the Director, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, U.S. Department of Energy under contract No. DE-AC02-05CH11231.
Keywords
- Above threshold ionization
- High-order harmonic generation
- Time-resolved velocity map imaging