Absolute measurement of hyperfine splittings of /sup 127/I/sub 2/ lines at h/spl lambda//spl ap/633 nm for improved wavelength standards

With the aid of two diode laser spectrometers around 633 nm, we report the measurement of the iodine hyperfine components of the R(60)8-4, R(125)9-4, P(54)8-4 transitions located -12 GHz from the classical red He-Ne laser stabilized on the R(127)11-5 transition of /sup 127/I/sub 2/, the P(33)6-3 transition roughly 1 GHz away, the P(39)6-3 transition 3.4 GHz above, and the R(59)8-4, P(53)8-4 transitions roughly 19 GHz above. The Doppler-free absorption signals were resolved using a third-harmonic detection technique and absolute frequency splittings by beat frequency techniques. The individual hyperfine transitions were linked by direct frequency measurements up to 16 GHz. The experimental uncertainty was typically below 8 kHz (<1.7/spl middot/10/sup -11/). First results on the strong group of transitions show a short-term stability better than that of the classical He-Ne laser, with a relative stability of 4/spl middot/10/sup -12/ for 1 s.