Radiative forces exerted on a two-level atom at rest

JOSIP SEKE

Daniel T. Stack

Over the past 30 years, optical manipulation of neutral atoms has been primarily performed with a monochromatic laser beam. The simplest tool for the control of atomic motion is the radiative force exerted by a monochromatic laser on a twolevel atom. The radiative force arises from absorption followed by spontaneous emission, and its magnitude is limited by the atom's excited state lifetime. The coherent momentum exchanges between light elds and atoms can be exploited to produce long-range optical forces much greater than the radiative force through the use of absorption-stimulated emission processes. Adiabatic Rapid Passage (ARP) is a long-existing method to invert the population of a two-level nuclear spin system. Its extension to the optical domain necessitates a frequency chirped light pulse to interact with a two-level atom via the dipole interaction. I will first present a numerical study of the properties of optical forces on moving atoms derived from purely stimulated processes produced by multiple ARP sequences. This will be followed by experimental observations of long-range ARP forces much larger than the radiative force in metastable helium. Sequences of properly timed laser pulses may be used for rapid deceleration of neutral atomic (or molecular) beams. | 171 pages

A. I. Alekseev

YE Yong-hua, Gao-Jian Zeng, Jinhui Li

We study the behaviour of an atomic wave packet in a circularly polarized light, and especially give the calculation of the radiative force exerted by the circularly polarized light on the atomic wave packet under the resonance condition. A general method of the calculation is presented and the result is interesting. For example, under the condition that the wave packet is very narrow or/and the interaction is very strong, no matter whether the atom is initially in its ground state or excited state, as time approaches to infinity, the resonance-radiation force exerted by the light on the atom approaches to zero. If the atom is initially in its ground state and excited state with the probability 1/2 respectively, and if the momentum density is a even function, then the resonance-radiation force exerted by the light on the atom is equal to zero.

Sunil Kumar, C. L. Mehta

Erik J. Bochove, Peter W. Milonni

We demonstrate, by solution of the Heisenberg equations of motion of the pseudo-spin and momentum operators of a two-level atom interacting with a phase- conjugate mirror (PCM) and a quantized radiation field, that a force is exerted by the PCM on the ground state atom. The expression found for the force is F=gRA(P1-P2)pvn̂, where P1 and P2 are the ground and excited state occupation probabilities, A=Einstein A-coefficient, pv=photon momentum at resonance, R=PCM reflectivity, n̂=unit outward normal to the PCM, and g=an aperture factor (g=9/64 for a dipole parallel to the plane of the PCM and solid angle=Ω= 2╔) . This result has a simple physical interpretation in terms of vacuum fields that are conjugated or amplified by the PCM (1,2).