Get 2-2021: State Primary Standard of the Unit of Length – the Meter

The principal stages in the process of improving the State Primary Standard of the unit of length – the meter are described. Results of investigations of the metrological characteristics of sources of standard radiation at wavelengths of 633 and 532 nm are presented. Investigations are conducted by means of an He–Ne/I₂ laser stabilized by a saturated absorption line in molecular iodine-127, a plant for the measurement of the frequency difference of sources of laser radiation, and a complex of equipment for measurement of the frequency (wavelength in a vacuum) of lasers in the wavelength range 500–1050 nm based on an optical frequency comb generator. As a result of investigations, the basic sources and limits of the components of the nonexcluded systematic error, standard Type B uncertainty, and mean Type A standard deviation are determined. A comparative analysis of the metrological characteristics of GET 2-2010 and GET 2-2021 is also presented, demonstrating the implementation of specific problem in the course of improvement of the standard. Thus, it became possible to reproduce the unit of length at a wavelength of 633 nm with standard deviation 1.6·10^–12 and at a wavelength of 532 nm with standard deviation 1.3·10^–12 and expand the range of transmission of the unit of length to sources of laser radiation and other modern high-precision means of measurement. The metrological characteristics of the standard whicha re obtained are not inferior to the best international analogues. GET 2-2021, the State Primary Standard of the unit of length – the meter, successfully underwent testing and was approved by order of Rossstandart.