Optically tunable hollow Gaussian beams using thin metal films

Abstract

We report the formation of optically tunable, smooth, hollow beams by reflection of a TEM00 Gaussian beam off a metal thin film. Hollow (doughnut-like) beams (HB) with controllable profiles are created by a phase distortion at the surface. Two regimes of operation are observed: below a certain power threshold, the hollow beam formation is reversible and optically tunable on a time scale of milliseconds; above that threshold, alterations on the film surface make the effect permanent. Optical control of the hollow beam shape is demonstrated by tuning the power of a second beam. High stability in the radial intensity profile and the possibility of adjusting the spatial distribution and aspect ratios make this technique promising for applications such as atom trapping and manipulation of Bose-Einstein condensates.