Penning plasma laser utilizing new transitions in the helium atom resulting in the emission of visible light

When an He–H₂ mixture was excited in a pulsed beam discharge, lasing was observed due to new helium lines at λ=728.1 nm (3¹S–2¹P) and 667.8 nm (3¹D–2¹P), as well as at 706.5 nm (3³S–2³P) observed earlier. The condition for a population inversion and lasing agreed with the theoretical model of a plasma recombination laser with a Penning clearing of the lower active levels, which was used to predict lasing due to these transitions.