Production of long-lived positronium states via laser excitation to 3$^3$P level

The 3$^3$P state of positronium is an intermediate level suitable for producing long-lived positronium states. On one hand, it can be used in a two-step laser excitation scheme from the ground state to Rydberg levels. On the other hand, excitation of positronium to 3$^3$P P level is a simple pathway for producing metastable 2$^3$S positronium atoms by spontaneous radiactive decay. In this work, experiments showing the production of such long-lived levels, using the 3$^3$P state as intermediate state, are presented. The characteristics of the two long-lived levels, in view of experiments of deflectometry/interferometry with positronium, are discussed.