Time-resolved photoelectron angular distributions and cross-section ratios of two-colour two-photon above threshold ionization of helium

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.

Keywords:

• high-order harmonic generation
• above threshold ionization
• time-resolved velocity map imaging

Acknowledgements

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.

Notes

‡On appointment as a Miller Research Professor in the Miller Institute for Basic Research in Science.

Additional information

Notes on contributors

Stephen R. Leone‡

‡On appointment as a Miller Research Professor in the Miller Institute for Basic Research in Science.