Optical trapping of neutral atoms and dielectric particles by radiation pressure

Arthur Ashkin

John E. Bjorkholm, Richard R. Freeman, Arthur Ashkin +1 more

Arthur Ashkin, J. P. Gordon

We prove an optical radiation Earnshaw theorem: A small dielectric particle cannot be trapped by using only the scattering force of optical radiation pressure. A corollary is that the gradient or dipole force is necessary to any successful optical trap. We discuss the implications of the theorem for recent proposals for the optical trapping of neutral atoms.

Harold J. Metcalf, P. van der Straten

Arthur Ashkin

The basic scattering and gradient forces of laser radiation pressure on atoms, dielectric particles, and biological particles are introduced, and experimental demonstrations of these forces are reviewed. As uses for radiation pressure forces, we consider the slowing, cooling, and trapping of neutral atoms at low temperatures; and the trapping and manipulation of dielectric and living biological particles in the Mie and Rayleigh size regimes.

Arthur Ashkin

Radiation pressure forces have been proposed for making stable optical traps for neutral atoms and other dielectric particles. Recently introduced optodynamic or alternating beam traps based on the scattering force are compared with cw traps based on the gradient force. Trapping experiments on micron-sized dielectric particles are described which demonstrate the basic principles of alternating beam light trapping. The relationship of these traps to the optical Earnshaw theorem is considered. The implications for trapping of recently demonstrated sources of slow atoms are also discussed.