title: Absolute frequency measurements of the 2(3)S1-->2(3)P 0,1,2 atomic helium transitions around 1083 nm.
abstract: We measure the frequency of the 2(3)S1-->2(3)P(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 2(3)P fine structure, we measure a centroid value of the 2(3)S-2(3)P frequency of 276 736 495 624.6(2.4) kHz, improving the previous interferometric measurement by 30 times. New accurate values of the 2(3)S-2(3)P and 2(3)P Lamb-shift energies are obtained.
authors.affiliation: Istituto Nazionale di Ottica Applicata (INOA), Largo E. Fermi 6, I-50125 Firenze, Italy.
authors.forename: P Cancio
authors.initials: PC
authors.lastname: Pastor
authors.forename: G
authors.initials: G
authors.lastname: Giusfredi
authors.forename: P
authors.initials: P
authors.lastname: De Natale
authors.forename: G
authors.initials: G
authors.lastname: Hagel
authors.forename: C
authors.initials: C
authors.lastname: De Mauro
authors.forename: M
authors.initials: M
authors.lastname: Inguscio