Measurement of the speed of light I. Introduction and frequency measurement of a carbon dioxide laser

This, and part II following, describe a determination of the speed of light made by measuring the frequency and wavelength of radiation from a CO₂ laser. This laser was operated on the 9.3 μm R(12) transition, and stabilized by reference to fluorescence in an external CO₂ absorption cell. The laser frequency was measured via a sequence of harmonic-mixing stages involving the HCN and H₂O lasers as transfer oscillators, and was found to be 32 176 079 482 ± 14 kHz ( ± 4.2 parts in 10¹⁰). A correction to this value of — 10 kHz is necessary to obtain the centre frequency of the CO₂ reference transition. The wavelength measurements and value of c are described in part II.