Emission of fast atoms from a cold Rydberg gas

Rydberg-Rydberg collisions in a cold, dense Rydberg gas can lead to the conversion of internal energy into center-of-mass energy of the colliding atoms, resulting in Rydberg-atom velocities much larger than the initial velocities in the gas. We prepare cold Rydberg-atom gases by laser excitation of laser-cooled atom clouds and use time-of-flight measurements to demonstrate the production of fast Rydberg atoms. The velocity distributions of Rydberg atoms emerging from the Rydberg-atom gases are obtained. State-selective field ionization spectra indicate a correlation between the production of fast Rydberg atoms and the presence of Penning ionization signatures. The dependence of the yield of fast Rydberg atoms on Rydberg atom density is measured.