Absolute frequency measurements of the 2³S₁-2³P_0,1,2 atomic Helium transitions around 1083 nm

We measure the frequency of the 2³S₁-2³P_0,1,2 transitions of helium in a metastable beam using an optical frequency comb synthesizer. The relative uncertainty of these measurements ranging from 5x10^-11 to 7x10^-12 is, to our knowledge, the most precise result for any optical helium transition. Considering existing accurate values of the 2³P fine structure, we measure a centroid value of the 2³S-2³P frequency of 276 736 495 624.6(2.4) kHz, improving the previous interferometric measurement by 30 times. New accurate values of the 2³S-2³P and 2³P Lamb-shift energies are obtained.