Focusing of a Rydberg Positronium Beam with an Ellipsoidal Electrostatic Mirror

Slow atoms in Rydberg states can exhibit specular reflection from a cylindrical surface upon which an azimuthally periodic potential is imposed. We have constructed a concave mirror of this type, in the shape of a truncated oblate ellipsoid of revolution, which has a focal length of (1.50 ±0.01 ) m measured optically. When placed near the center of a long vacuum pipe, this structure brings a beam of n =32 positronium (Ps) atoms to a focus on a position sensitive detector at a distance of (6.03 ±0.03 ) m from the Ps source. The intensity at the focus implies an overall reflection efficiency of ∼30 %. The focal spot diameter (32 ±1 ) mm full width at half maximum is independent of the atoms' flight times from 20 to 60 μ s , thus indicating that the mirror is achromatic to a good approximation. Mirrors based on this principle would be of use in a variety of experiments, allowing for improved collection efficiency and tailored transport or imaging of beams of slow Rydberg atoms and molecules.