1. R. B. Armstrong and H. L. Welsh, quoted by C. B. Moore, J. Chem. Phys. 49, 1111 (1968).
2. H. J. Gerritsen and M. E. Heller, Appl. Opt. Suppl. #2, 73 (1965). See also K. Sakurai and K. Shimoda, Japan J. Appl. Phys. 5, 744 (1966).
3. J. L. Hall and Ch. Bordé, Phys. Rev. Letters 30, 1101 (1973).
4. In their June, 1973, Paris meeting, the Comité Consultatif pour la Définition du Mètre recommended a wavelength value for the methane P(7) F component, λ = 3392231.4 x 10-12 m. They also recommended a value for a certain iodine transition at.633 µm and for the speed of light, c = 299,792,458 m/sec. The assigned fractional uncertainties of these quantities is ±4 x 10-9.
5. J. L. Hall, IEEE J. Quant. Electron. QE4, 638 (1968).