Anomalous strong-field ionization of oxygen

Abstract

Circularly polarized light, does not allow the ionized electron to ever return to the ion core. Thus, to test for dissociative recombination, we measured the ion yields of Xe and O/sub 2/ for both linear and circular polarization. Circular polarization shows almost the same degree of suppression. From this, we conclude that dissociative recombination cannot account for the bulk of the suppression of the O/sub 2/ ion yield. For this and a variety of other reasons, it is becoming increasingly important to have an established model for the tunneling rate of molecules in strong laser fields. To address this problem, we have developed a model to calculate the tunneling rate of an arbitrary one-dimensional potential in a strong electric field. We calculate the spectrum of a potential at a given field strength by choosing an energy and numerically integrating the Schrodinger equation across the potential far enough into the allowed region to where the applied electric field dominates. At this point, the solutions of Schrodinger's equation are the well known Airy's functions. If we simply match to these functions, we can determine the free amplitude of the wavefunction. The square of the ratio of the bound to be free character will give a measure of the bound strength of the wavefunction. Plotting this ratio as a function of energy gives the spectrum of the potential. As expected, the spectrum shows resonance peaks near the zero field bound states, but with nonzero widths from which we can determine ionization rates. Applying this model to Xe and O/sub 2/ confirms the fact that they should have nearly identical ionization rates in a strong laser field. Thus, the large discrepancy in rate clearly points to the existence of new physics in the behavior of molecules in strong laser fields.