Electron Rescattering from Molecules in Intense Laser Fields

C.L. Cocke
(Physics Department, Kansas State University)

One process whereby molecules are multiply ionized by pulses of intense laser radiation is electron rescattering. An electron removed from the neutral molecule by the laser field returns to ionize or excite the molecule further through inelastic electron-molecular-ion scattering. Since these electrons revisit the ion at multiples of half the laser period (1.3 fs for 800 nm light), this pulsed excitation source provides a fast-ticking clock whereby the vibrational motion of the disintegrating molecule can be timed. In the case of the hydrogen (or deuterium) molecule, the resulting kinetic energy release (KER) of pairs of protons (deuterons) generated in the double ionization of the molecule can be used as a measure of the internuclear distance at which the final ionization occurs. I will discuss some recent experiments in which the full momentum vectors of the coincident ion pairs are used to provide both the KER and the the dependence of the ionization process on the angle between the the electric field vector and the internuclear vector. The spectra show three distinct mechanisms for double ionization: rescattering, sequential ionization and enhanced ionization. Each of these generates a characteristic signature in the KER and angular spectrum. Comparison of the experimental results with a quantitive model reveals that good understanding of these processes is in hand. Extension of this work to other more complex molecules such as nitrogen and oxygen will also be presented.

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 DAMOP, May 2004 in Tucson, AZ.

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