An high precision interferometric system for nanodeplacement measurements

This paper presents the principle of an air wavelength standard for high accuracy length metrology. According to the definition of the metre, 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. We now have adapted this source to a commercial interferometric system working at 633 nm. Length variation measurements in air have been made. Results show that the wavelength of our source is insensitive to slow variations of the refractive index of air at a level of 10/sup -8/, giving the possibility of making distance measurements in air without the need to make any index correction.