Krypton wavelength standard

The frequency stability obtained up to now is already better than 1x10 and therefore exceeds the accuracy of the optical wavelength standard (red krypton line) by more than three orders of magnitude 333b, c)... 

In 1960, the SI unit of length was redefined. While keeping the metre as the unit of length, it is now defined as 1 650763.73 wavelengths of the light emitted in vacuo by krypton-86. This is a sensible standard, because it can be reproduced in any laboratory in the world. 

Since 1960 the wavelength of the spectral lines of the krypton-86 isotope has been used as the standard for the length of the meter. One meter is now defined as 1,650,762.73 wavelengths of the reddish-orange spectral line of the Kr-86 isotope. 

Wavelength equivalent of one electron volt = 1.2398 x 10 " cm Standard of length, krypton 84 red line = 6057.802106 A (adopted October 1960 by the 11th General Conference on Weights and Measures, Paris)... 

The universal standard of length is the metre, and the definition of this in terms of wavelength of light was agreed by all countries in 1960. The metre was defined at this time as 1 650763.73 wavelengths of the orange radiation of the krypton-86 isotope in vacuo. At the same time the yard was defined as 0.9144 m, which gives an exact conversion of 1 inch = 25.4mm. 

In 1960 it was internationally agreed that the fundamental unit of length, the meter, would be defined in terms of the orange-red spectral line of krypton-86. In fact, 1 meter is exactly 1,650,763.73 wavelengths (in vacuo) of this line. This agreement replaced the standard platinum-iridium meter located in Paris. 

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