Laser induced line narrowing in three-level systems: Application to the determination of the wavenumber of the 3s 2-2p 4 neon line (λ = 6328 Å)

The Doppler-free absorption line narrowing technique (A.L.N.) is applied to the ²⁰Ne (3s ₂-2p ₄-1s ₅) three-level system, using a ¹²⁷I ₂ stabilized He-Ne laser (λ = 6328 Å) and a tunable single-frequency cw dye laser (λ = 5945 Å). The relative frequency positions of the ²⁰Ne 3s ₂-2p ₄ line and of some iodine hyperfine components are measured with an uncertainty of 1 MHz. The wavenumber of the ²⁰Ne line at low pressure (0.2 Torr) is deduced from these measurements and is found to be σ( ²⁰Ne, 3s ₂-2p ₄) = 1579800.060 ± 0.005 m ^-1. With regard to the previous results, the accuracy is increased by two orders of magnitude.