First observation of resonant excitation of high-nstates in positronium

We have performed the first excitation of high-n states of positronium using resonant, two-photon excitation applied to the n=1 to 2 and 2 to n transitions. Absolute values for the line positions were quantitatively determined for n=14 and 15 and compared well with calculated predictions. The prediction of the ${\mathit{n}}^{\mathrm{-}3}$ scaling of the relative transition rates was observed for n=12 to 19.