Describe five methods of interacting with a system
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2.1 Molecular Hamiltonian in the presence of a laser field
Many forms of the Hamiltonian operator describing a system interacting with a radiation field are currently in use [1, 4, 17, 18]. These are defined within either of two descriptions: One is fully quantized and treats both the laser field and the molecular system quantum mechanically. The other is semiclassical and assumes at the outset a classical field while the charged particles are treated quantum mechanically. We recall here the expression of the Hamiltonian of a laser-driven molecule written in the semiclassical description; this will serve to lay the ground work for the construction of the models encountered in the subsequent Sections. It is to be recalled also that many equivalent forms of the radiative interaction exist, corresponding to different choices of the electromagnetic field’s gauge. We will systematically refer to the so-called Coulomb length gauge in writing the interaction between a charged particle of a molecule and a radiation field. Also, only electric dipole interactions are considered within the so-called long-wavelength approximation.