Laser measurement of the speed of light (Evenson)
Medida de la velocidad de la luz con láser (Evenson)
- Date
- 1972 · confidence high
- Place
- Boulder, Colorado, United States
- Credited to
- Kenneth Evenson and colleagues (NBS)
- Field
- Knowledge & symbols
What was discovered
They measured the frequency and wavelength of a methane-stabilised helium-neon laser, obtaining c = 299,792,456.2 ± 1.1 m/s, a hundred times more precise than before. It showed that the wavelength and frequency of light could be compared exactly.
The experiment was carried out at the NBS laboratories in Boulder; the general conference adopted in 1975 the value of 299,792,458 m/s and in 1983 the metre was fixed.
What it led to
- the recommended value of c (1975) with an uncertainty of 4 mm/s
- definition of the metre by the speed of light (1983)
- frequency chains linking microwaves and light