A transfer standard of the Mètre: an air wavelength reference

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the Mètre, nanometric accuracy by interferometric measurement techniques can be reached only for measurements made under vacuum or by taking into account the fluctuations of the refractive index of air. We have developed a new type of laser source whose wavelength is insensitive to slow fluctuations of the refractive index of air. The sensitivity of our air wavelength standard to some characteristics (such as temperature, pressure, ageing behaviour...) has been measured. Results show that the relative uncertainty level of the wavelength of our source is below 10−8.