Strong-field ionization and gauge dependence of nonlocal potentials

Abstract

Nonlocal potential models have been used in place of the Coulomb potential in the Schrodinger equation as an efficient means of exploring high field laser-atom interaction in previous works. Although these models have found use in modeling phenomena including photo-ionization and ejected electron momentum spectra, they are known to break electromagnetic gauge invariance. This paper examines if there is a preferred gauge for the linear field response and photoionization characteristics of nonlocal atomic binding potentials in the length and velocity gauges. It is found that the length gauge is preferable for a wide range of parameters.

Ionisation of H 2 O by a strong ultrashort XUV pulse: a model within the single active electron approximation

“…The problem of the gauge invariance in the context of nonlocal potentials has been discussed in great detail in various references. 9,17,18 In particular, it is shown in 9 that it is possible to formulate our separable potential model in various ways that can be grouped into two families such that within a given family, the length and velocity gauge formulations give the same value for the observables. This shows clearly the non-existence of a privileged gauge but does not solve the problem of the "global" gauge invariance since formulations belonging to the first and the second family give different results for the observables.…”