Abstract
We study the gauge invariance of the laser-matter interaction. The velocity gauge, where the vector potential is expanded to the order with respect to the spatial coordinate, and the length gauge, where the electric and magnetic fields are expanded to the and orders, respectively, are mutually gauge transformed, describing the physically equivalent situation. The latter includes up to the electric -pole and magnetic -pole interactions as well as two extra terms. The finding serves to develop consistent nonperturbative simulation methods beyond the electric dipole approximation.
- Received 23 June 2018
DOI:https://doi.org/10.1103/PhysRevA.98.063410
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