ABSTRACT
The National Bureau of Standards has had a long history of interest in the speed of light. As early as 1907, Rosa and Dorsey determined the speed of light from the ratio of the capacitance of a condenser as measured in electrostatic and electromagnetic units. By the late 1960s, lasers stabilized in frequency to atomic and molecular resonances were becoming reliable research tools. These could be viewed as providing stable reference for either optical frequency or wavelength. This duality of frequency and length produced the suggestion that a simultaneous measurement of frequency and length for the laser transition would yield a good measurement of the speed of light. The measurement of the speed of light by the Boulder group involved the development of a new method. The approach taken was to synthesize signals at progressively higher and higher frequency using harmonic-generation-and-mixing methods and to lock the frequency of a nearby oscillator or laser to the frequency of this synthesized signal.
