Improved far-field optical trap for cold atoms (molecules) with phase-modulated circular aperture diffraction

Abstract

We propose a scheme to trap cold atoms (or molecules) by using an improved red- or blue-detuned far-field optical trap, which is formed by an optical system composed of a binary phase plate and a circular aperture illuminated by a plane light wave. We calculate the relative intensity distribution of the far-field trap and study its dependence on the phase $\ensuremath{\varphi}$ of the binary phase plate. Our study shows that the binary phase plate can be used to improve some geometric and optical parameters of the far-field optical trap, and realize the evolution of the far-field optical trap from a red-detuned trap to a blue-detuned one. In particular, when the phase $\ensuremath{\varphi}$ of the binary phase plate is changed from 0 to $\ensuremath{-}\ensuremath{\pi}$, the maximum intensity of the far-field trap and its well depth will be enhanced by $\ensuremath{\sim}4$ times, and the corresponding trapping volume will be increased by $\ensuremath{\sim}8$ times, with respect to a trapping beam obtained from the diffraction by a circular aperture.