Generation of a localized hollow laser beam using crossed nonlinear optical crystals

A nonlinear optical approach to generate a localized hollow laser beam and its array using crossed nonlinear ZnSe crystals is proposed. We calculate the intensity distributions of the hollow beam and its propagating properties in free space, and study the dependences of the dark spot size of the hollow beam on the incident beam waist radius and the crystal length. Our studies show that the longitudinal size of the hollow beam can be reduced by ∼660 times than that generated by a single nonlinear crystal. Such laser beam with a dark hollow region and a large intensity gradient can be used to trap cold neutral atoms, molecules and microscopic particles.