| Summary: | A Surko-type positron trap has been used to produce intense positron pulses, and thus a dilute positronium (Ps) gas in vacuum with an initial density of 10^7 cm-3. This gas was excited with lasers for a variety of experiments. n = 2 atoms were prepared using a single-photon excitation scheme (1S to 2P) in controlled electric and magnetic fields for studies of Stark and Zeeman effects, measurements of Ps cooling via Doppler spectroscopy, and for the produciton of ensembles of atoms in pure 2S states. The first measurements of Ps excitation to specific Rydberg-Stark states were performed via a two-color two-photon excitation scheme ( 1S to 2P to nS/nD). Ps atoms in low-field–seeking Rydberg Stark states were prepared at the entrance of an electrostatic quadrupole guide which was used to control the trajectories and velocity distributions of the Ps atoms. These advances, together with the results from numerical simulations, suggest that these methods could be used in to perform Stark deceleration and trapping of Rydberg Ps, high-precision Ps spectroscopy, and to create positron-atom bound states.
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