Measuring the speed of light by independent frequency and wavelength determination

The most recent measurements of the speed of light have been based on a separate determination of the frequency and wavelength of laser radiation. As a result of the increased precision and the imbalance in precision between frequency and wavelength measurements, the speed of light in a vacuum c (299,792,458 m/s) has been proposed as a defined standard constant connecting time and length measurements. This paper reports on a student experiment at the intermediate undergraduate level that contains the fundamental elements found in the most recent determination of c. Harmonic mixing is utilized for the frequency determination and interferometry for the wavelength determination of a 9‐GHz electromagnetic source.