Extreme-ultraviolet laser metrology of O I transitions

Some 16 transitions in atomic oxygen originating from its 3 P ground state were measured using a tunable narrow-band extreme-ultraviolet laser source, with an unprecedented accuracy of �λ/λ = 8 × 10 −8 . The results are relevant for comparisons with spectral absorption features observed in the line of sight of quasars, in order to test a possible variation of the fine-structure constant α on a cosmological time-scale.