Laser Interactions with Atomic and Molecular Positronium

Positronium (Ps), the bound state between an electron and its antiparticle, the positron, may be efficiently created by bombarding certain porous materials with intense bursts of positrons obtained from a positron accumulator. Using a Surko-type buffer gas trap we have produced a high-density pulsed positron beam makes it possible to study interactions between Ps atoms, allowing for measurements of molecular Ps$_{2}$ formation and Ps-Ps scattering. Moreover, even at a low spatial density the $\sim $ 1 ns wide pulses are well suited to laser spectroscopy of Ps atoms; numerous experiments are possible, including measurements of atomic energy intervals (e.g., the hyperfine interval), the effects of confinement on transition wavelengths, Ps cooling and the production of long-lived Rydberg Ps atoms. High density pulses used with lasers have also been used to perform optical spectroscopy on the Ps$_{2}$ system.