An intense collimated beam of metastable helium atoms by two-dimensional laser cooling

Abstract

A compact apparatus has been developed to generate an intense beam of helium atoms in the metastable 2 3S state. A liquid nitrogen cooled DC discharge with a 0.25 mm diameter nozzle produces a beam with an intensity of 2 × 10 14 metastable atoms per second per sterad, an average velocity ν = 1030 m/s and a velocity spread of Δν FWHM ν =0.3 . Transverse two-dimensional laser cooling using curved wavefronts has been applied to capture atoms within a 30 mrad cone, to collimate the atomic beam and to enhance its intensity by a factor 50. An atomic beam with a cross section of 3 × 3 mm 2 and an intensity of 1 × 10 10 metastable triplet atoms per second per mm 2 has been realised using a laser cooling section with an interaction length of 18 cm.