Ross E. Sheldon
Tests of Quantum Electrodynamics Using n = 2 Positronium
Lokesh Gurung
Precision Microwave Spectroscopy of the Positronium n = 2 Fine Structure
Alberto M. Alonso
Spectroscopy and manipulation of positronium in excited states
Ben S. Cooper
Laser excitation of positronium produced by various materials at a range of temperatures