Different forms of laser–matter interaction operators and expansion in adiabatic states
Department of Physics and Astronomy, Aarhus University, 8000, Aarhus C, Denmark
Accepted: 24 December 2020
Published online: 8 April 2021
The interaction between atoms and molecules and intense laser pulses is typically described in either the velocity gauge, length gauge or in the Kramers–Henneberger frame. Here, certain relations between these forms are discussed. In particular expansions of the solution to the time-dependent Schrödinger equation in adiabatic states are considered. Such expansions in adiabatic states could be expected to be attractive for intense long-wavelength infrared laser pulses, where the external field changes on a slow timescale compared with the electron motion. It is shown that an expansion in velocity gauge adiabatic states gives the equations of motions that follow from an expansion in field-free states and by expressing the interaction operator in the length gauge. Likewise, it is shown that an expansion in the Kramers–Henneberger frame adiabatic states gives the equations of motion following an expansion in field-free states and using the velocity gauge interaction operator. Finally, an alternative form for the laser–matter interaction operator is considered, which is similar to the velocity gauge, but shifts the canonical momentum operator by the impulse associated with the Kramers–Henneberger interaction operator, rather than that of the electric field as is the case in the velocity gauge.
© The Author(s), under exclusive licence to EDP Sciences, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2021