Di-positronium Molecules and the Quest for the Annihilation Gamma Ray Laser

Positronium, (atomic symbol Ps) is a purely leptonic hydrogen-like atom formed from an electron and its positron antiparticle. A few years ago the production of di-positronium molecules demonstrated the possibility of experiments with a dense gas of positronium. The enabling technologies included techniques for moderating, trapping, accumulating, compressing, and bunching positrons obtained from high energy beta-decay or pair-produced sources. Recent experiments using nanosecond pulses containing 20 million positrons implanted into a solid target allowed production of nearly 100% polarized positronium atoms via Ps-Ps spin exchange collisions, and revealed a production rate of positronium in vacuum from a Si target that is nonlinear in the positron density. We are now measuring the Lyman-alpha-like transition in the di-positronium molecule predicted at an optical wavelength of 251 nm. Increasing in the density of the matter-antimatter gas to around that of ordinary air will enable making short lived Ps Bose-Einstein condensates at room temperature. Continuing efforts to increase the strength and quality of primary positron sources suggest the eventual possibility of coherent gamma ray laser bursts of electron-positron annihilation radiation.