Laser-modified Long-range Forces Between Neutral Atoms

Abstract

Modification of the long-range forces between atoms by laser light has been considered by Thirunamachandran (1980). More recently, Grossel and van Labeke (1994) treated the modified interaction between a conducting surface and an atom. In the present paper we establish the formulas for laser-modified Casimir forces between neutral atoms using a semiclassical formalism. These forces appear as a result of interaction of atomic dipoles with the background vacuum, in which spectral density is modified by the laser field. In particular, the interaction potential between two neutral atoms displays non-monotonic behaviour in an external field for certain polarisations. The averaging of this result over the mutual position of the atoms coincides with Thirunamachandran's result for the laser-modified Casimir forces. We give estimates for the value of this interaction, which may dominate the Casimir force for distances comparable to the wavelength. The validity of the semi-classical method is proven by comparison with the results of second-order perturbation theory. Furthermore, the method is used to calculate the external field modification of dispersive forces between a magnetically polarisable body and an electrically polarisable one and a chiral system coupled to both electric and magnetic fields.