Role of interaction time in light pressure force on atoms

In this paper we studied the possibility of an analytical description of the light pressure forces acting on a two-level atom in the field of a transversely modulated monochromatic running wave. It has been shown that in three cases - small interaction time (Ω^-1≪T≪γ^-1), long interaction time (γ^-1≪T) and moderate interaction time (γ^-1≲T) - the light pressure force can be described by simple analytical expressions, where Ω is the detuning and γ is the line half-width. It has been shown that the universally accepted expressions for the light pressure forces are a zero-order term of expansion of `real' force into powers of inverse interaction time T^-1. The first-order corrections have been calculated. The inclusion of these corrections gives rise to dissipative terms in the gradient force. The reflection of atoms from a light-induced mirror has been numerically simulated. The results are in good agreement with the analytical expressions obtained. It has been shown that after a moderate interaction time (γ^-1≲T) the mirror-like character of reflection is disturbed. The nonadiabatic corrections to the light pressure force obtained in this study describe this deviation well.