Time sequencing short pulse double ionization mechanisms in molecular hydrogen
J.R. Macdonald Laboratory, Department of Physics, Kansas State University, Manhattan, KS 66506, USA
Heavy particle motion in the simplest of all molecules, H2, can be monitored in real time using the optical period of radiation in a short intense-field pulse. If the molecule is doubly ionized, it produces two protons whose kinetic energy release (KER) is approximately a measure of the internuclear distance at which the molecule reached the double ionization potential curve. We have used COLTRIMS momentum imaging techniques to record the comprehensive vector momentum spectra of pairs of coincident protons from pulses of 800 nm radiation of pulse duration between 8 and 35 fs and intensities between 1 and 8 x 1014 W/cm2 to study this decay channel. We isolate and identify in the spectra three distinct double ionization mechanisms: enhanced ionization, rescattering ionization and sequential ionization. Each produces very unique and recognizable features which can be used to deduce the time history of the ionization process on a fs time scale. Comparison of the experimental results with a quantitative model  will be presented.
 X.-M. Tong and C.D.Lin, Phys. Rev. A , 2004 (submitted).
This work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,
Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.
Submitted to Ultrafast X-Ray Science, April 2004 in San Diegeo, CA.
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