We report on a detailed study of the focusing properties of inhomogeneous magnetic fields. The experiment is performed using cold cesium atom clouds released from a magneto-optical trap. The sample longitudinal distributions are being compressed under the influence of a pulsed parabolic magnetic potential. Achromatic imaging potentialities are demonstrated. Analogies with usual optics are pointed out. A velocity compression is obtained, leading to a cloud longitudinal effective temperature down to 220 nK for a proper choice of the experimental parameters. The observation of strong compressions is corroborated by numerical simulations in excellent agreement with the experimental data. The principle of the method is presented in view of an elementary one-dimensional model and its limits are discussed.

• Received 5 October 1998

DOI:https://doi.org/10.1103/PhysRevA.59.4636