Self-deformation of Kramers–Henneberger atoms in focused laser beams of circular polarization

In intense field laser dressing of atoms, electrons follow the laser oscillation and undergo quiver motion just like free electrons but still weakly bound to the atomic core, thus forming a set of specific dressed states named Kramers–Henneberger (KH) states. For decades, it was widely believed that ground KH state hydrogen atoms in a circularly polarized laser field exhibit the symmetric structure of a perfect ring. But our study shows this is not a common structure because of the fact that KH atoms can only exist in intense laser fields which are practically focused laser beams. In focused laser field, KH state electrons have to experience the ponderomotive force, which might polarize the atom and reshape its structure. Only in a laser beam with small quiver amplitude and high frequency, can the symmetric circular structure be fully or partially preserved.