Measurement and direct regulation of the velocity of a fast beam using doppler-tuned laser photon-atom interactions

An optical method is described that uses the Doppler shift to measure the velocity of a fast particle beam merged with a photon beam from a laser. The Doppler-tuned resonance signal is used in a feedback loop to regulate directly the velocity of the beam. The method is demonstrated using a beam of ⁴He atoms pumped by CO₂ laser photons into high Rydberg pure quantum states. Applications to other areas of fast beam physical research are discussed.