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 similar to 30%. The focal spot diameter (32 +/- 1) mm full width at half maximum is independent of the atoms' flight times from 20 to 60 mu 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.