Laser-induced resonant transition at 470.724 nm in thev=n-l-1=2 cascade of metastable antiprotonic helium atoms

A laser-induced resonant transition in metastable antiprotonic helium atoms has been found at a wavelength of 470.724±0.002 nm and assigned to the transition (n,l)=(37,34)→(36,33). From the time evolution of the laser resonance intensity, the decay rate of the (37,34) state was determined to be 1.17±0.09 μ${\mathrm{s}}^{\mathrm{-}1}$, about 60% larger than the theoretical radiative decay rate. The sum of the initial populations in the v=n-l-1=2 decay chain was 23±4% of the total number of metastable atoms formed.