Longitudinal focusing of an atomic cloud using pulsed magnetic forces

We report on a detailed study of the focusing properties of inhomogeneous m agnetic fields. The experiment is performed using cold cesium atom clouds r eleased from a magneto-optical trap. The sample longitudinal distributions are being compressed under the influence of a pulsed parabolic magnetic pot ential. Achromatic imaging potentialities are demonstrated. Analogies with usual optics are pointed out. A velocity compression is obtained, leading t o a cloud longitudinal effective temperature down to 220 nK For a proper ch oice of the experimental parameters. The observation of strong compressions is corroborated by numerical simulations in excellent agreement with the e xperimental data. The principle of the method is presented in view of an el ementary one-dimensional model and its limits an discussed. [S1050-2947(99) 05206-3].