Seeded supersonic alkali atom beams

A seeded supersonic beam source for alkali atoms is described which provides velocities up to ∼ 5 km/sec. Potassium or rubidium vapor at ∼ 0.02 to 0.2 Torr is mixed with a diluent gas of H2, He, or Ar at ∼ 800 Torr and expanded through a pinhole nozzle. The beam properties are found to compare well with the simple theory of isentropic expansions. Typically, the alkali flux is ∼ 1016 atoms sr−1 sec−1 and the velocity spread is ∼ 8% (FWHM).