Theory of the radiation pressure on dielectric surfaces

The radiation pressures exerted by light beams incident normally on dielectric surfaces are calculated by evaluation of the quantum-mechanical Lorentz force. The free-space surface of an almost transparent dielectric and the interface of a lossy dielectric with a transparent medium are treated in detail. Light beams in the forms of a short single-photon pulse and a continuous-mode narrow-band coherent excitation are considered. The use of a pulse excitation enables discrimination of the surface and bulk contributions to the force. It is shown that the surface force is directed inwards to the dielectric for entrance and exit of the pulse from and to free space, contrary to the conclusions of some earlier work. For the interface of lossy and transparent dielectrics, it is shown that the high-reflectivity mirror modelled by an appropriate limit of the lossy dielectric experiences a force enhanced by the refractive index of the transparent medium, in agreement with experiments on a mirror suspended in liquid dielectrics. The results for the Lorentz force are used to identify the effective momenta of photons in dielectrics.