Light Forces

V. E. Shapiro

The work is aimed at drawing attention to peculiar properties and the considerable magnitude of the vortical part of the light force which make it important for light-induced effects of atomic drift, cooling and trapping in gas. The author introduces basic notions that specify the vortical force, determine its properties and the functional structure and give estimates in the weak-field limit. The vortical force like the light gradient force and the light frictional force sharply increases in the light field resonantly exciting the atom, but depends quite differently on the resonance detunings, wavevectors, polarisation and light wave phases. The results give insight into how to control the vortex effect of light under what conditions it dominates critically the effect of light friction and gradient forces.

J. Weiner

Atom traps Light forces It is well known that a light beam carries momentum and that the scattering of light by an object produces a force. This property of light was first demonstrated by Frish [139] through the observation of a very small transverse deflection (3 × 10 –5 rad) in a sodium atomic beam exposed to light from a resonance lamp. With the invention of the laser, it became easier to observe effects of this kind because the strength of the force is greatly enhanced by the use of intense and highly directional light fields, as demonstrated by Ashkin [20, 21] with the manipulation of transparent dielectric spheres suspended in water. The results obtained by Frish and Ashkin raised the possibility of using light forces to control the motion of neutral atoms. Although the understanding of light forces acting on atoms was already established by the end of the 1970s, unambiguous demonstration of atom cooling and trapping was not accomplished before the mid 1980s. In this section we discuss some fundamental aspects of light forces and schemes employed to cool and trap neutral atoms. The light force exerted on an atom can be of two types: a dissipative, spontaneous force and a conservative, dipole force. The spontaneous force arises from the impulse experienced by an atom when it absorbs or emits a quantum of photon momentum.

S. Brandt, Hans Dieter Dahmen

Adam T. Black, James K. Thompson, Vladan Vuletić

We study resonator-induced light forces arising from cooperative atom–light interaction. For such collective processes, the force on the sample can be orders of magnitude larger than the sum of conventional light forces on individual atoms. Since resonator-induced light forces can be dissipative even when the incident light is far detuned from atomic transitions, they may be applicable to target particles with a complex level structure. (Some figures in this article are in colour only in the electronic version)