Selection of particles by a gradient force in the near field of laser light
Klimov V. V., Letokhov V. S.
The spatially nonuniform intensity distribution of laser light diffracted by an aperture small in comparison with the wavelength leads to a resonant selection of atoms by virtue of a dipole gradient force acting on an atom. As a result, the effective cross section for the transmission of an atom through the aperture either increases or decreases from the geometric cross section. The direction of the change depends on the detuning of the frequency of the laser field from the frequency of the atomic transition. The effect is sensitive to both the species of the atom and its velocity.