An Atomic Lens Using a Focusing Hollow Beam

We propose a new method to generate a focused hollow laser beam by using an azimuthally-distributed 2π-phase plate and a convergent thin lens, and calculate the intensity distribution of the focused hollow beam in free propagation space. The relationship between the waist w₀ of the incident collimated Gaussian beam and the dark spot size of the focused hollow beam at the focal point, and the relationship between the focal length f of the thin lens and the dark spot size are studied respectively. The optical potential of the blue-detuned focused hollow beam for ¹⁸⁵Rb atoms is calculated. Our study shows that when the larger waist w of the incident Gaussian beam and the shorter focal length f of the lens are chosen, we can obtain an extremely-small dark spot size of the focused hollow beam, which can be used to form an atomic lens with a resolution of several angstoms.