Nonlinear focusing of atom clouds by a short-focal-length magnetic lens

Utilizing the Stern-Gerlach effect, magnetic lenses are used to focus atom clouds, reducing their dimensions, and boosting the central cloud density. In this research, a theoretical model based on nonlinear Zeeman splitting in high-intensity magnetic fields is established to explore the nonlinear focusing of a tightly focused magnetic lens. The research concentrates on the motion and focusing of ⁸⁷Rb atoms in various Zeeman substates within an atom fountain under pulsed magnetic fields and establishes a correlation between the field curvature and the effective focal length. The nonlinear model has been validated in the experiment conducted in the fountain. Atoms in different Zeeman substates were selectively focused by the magnetic lens which has applications in precise manipulation of atoms including collimation, concentration, and spatial filtering. A spatial filter based on this method has been deployed in the phase-shear atomic interferometer to prepare an atom cloud in a pure Zeeman substate.