Nonadiabatic tunneling in circularly polarized laser fields: Derivation of formulas

TL;DR

This paper develops an analytical theory for strong field ionization of degenerate p orbitals by circularly polarized lasers, demonstrating gauge invariance and showing preferential ionization of counter-rotating electrons, with implications for non-adiabatic regimes.

Contribution

It provides a gauge-invariant analytical approach for p orbital ionization in circularly polarized fields, extending PPT theory and highlighting electron rotation effects.

Findings

Ionization preferentially removes counter-rotating electrons.

Results are gauge invariant under the dipole approximation.

Strong sensitivity of ionization to electron rotation sense.

Abstract

We provide detailed analysis of strong field ionization of degenerate valence p orbitals by circularly polarized fields. Our analytical approach is conceptually equivalent to the Perelomov, Popov, and Terent'ev (PPT) theory and is virtually exact for short range potentials. After benchmarking our results against the PPT theory for s orbitals, we obtain the results for p orbitals. We also show that, as long as the dipole approximation is valid, both the PPT method and our results are gauge invariant, in contrast with widely used strong field approximation (SFA). Our main result, which has already been briefly outlined in [I. Barth and O. Smirnova, Phys. Rev. A 84, 063415 (2011)], is that strong field ionization preferentially removes electrons counter-rotating to the circularly polarized laser field. The result is illustrated using the example of Kr atom. Strong, up to one order of magnitude, sensitivity of strong field ionization to the sense of electron rotation in the initial state is one of the key signatures of non-adiabatic regime of strong field ionization.