Zeeman deceleration of electron-impact-excited metastable helium atoms

We present experimental results that demonstrate—for the first time—the Zeeman deceleration of helium atoms in the metastable 2³S₁ state. A more than 40% decrease of the kinetic energy of the beam is achieved for deceleration from 490 m ^-1 to a final velocity of 370 m s^-1. Metastable atom generation is achieved with an electron-impact-excitation source whose performance is enhanced through an additional discharge-type process which we characterize in detail. Metastable helium is efficiently generated even in a mixture of other noble gases that have much lower excitation energies. Comparison of deceleration data at different electron beam pulse durations confirms that a matching between the initial particle distribution and the phase-space acceptance of the decelerator is crucial for the production of a decelerated packet with a well-defined velocity distribution. The experimental findings are in good agreement with three-dimensional numerical particle trajectory simulations.