Quasistatic limit of the strong-field approximation describing atoms in intense laser fields: Circular polarization

TL;DR

This paper extends the understanding of ionization rates in intense laser fields by deriving analytical expressions for circular polarization, showing a different frequency dependence than linear polarization in the quasistatic limit.

Contribution

It provides new analytical formulas for ionization rates under circular polarization, highlighting their dependence on higher powers of laser frequency in the quasistatic limit.

Findings

Ionization rate proportional to higher powers of laser frequency for circular polarization.

Derived asymptotic expressions are accurate in the quasistatic limit.

Expressions do not involve summations over multiphoton contributions.

Abstract

In the recent work of Vanne and Saenz [Phys. Rev. A 75, 063403 (2007)] the quasistatic limit of the velocity gauge strong-field approximation describing the ionization rate of atomic or molecular systems exposed to linearly polarized laser fields was derived. It was shown that in the low-frequency limit the ionization rate is proportional to the laser frequency (for a constant intensity of the laser field). In the present work I show that for circularly polarized laser fields the ionization rate is proportional to higher powers of the laser frequency for hydrogenic atoms. The new analytical expressions for asymptotic ionization rates (which become accurate in the quasistatic limit) contain no summations over multiphoton contributions. For very low laser frequencies (optical or infrared), these expressions usually remain with an order-of-magnitude agreement with the velocity gauge strong-field approximation.