Slowing Supersonic Beams via Elastic Reflection from Moving Crystals: An Atomic Paddle

We report the slowing of a supersonic beam of helium using specular reflection from a receding crystal. We use an Even-Lavie pulsed supersonic nozzle to generate a 511 m/s beam of helium at 250 mK. The beam is reflected from a Si(111)-H(1x1) crystal prepared \textit{ex-situ }via wet etching and mounted on the tip of a spinning rotor. By controlling the rotor velocity we can continuously tune the velocity of the slowed beam. We have slowed the beam to as low as 246 m/s without affecting its temperature. Applications to slowing of molecular hydrogen and deuterium will be discussed.