Metrological basis of laser frequency measurements in the USSR

The subject of high-precision laser frequency measurement is considered. The laser multiplication chain is presented and the main parameters listed. The idea of phase locking the laser chain is explained. The chain is included into the State Time and Frequency Standard and allows the measurement of laser frequencies in the range up to 3 × 10
¹³
Hz with an error of less than 1 × 10
^-12
and in the range up to 9 × 10
¹³
Hz with an error not greater than 2 × 10
^-11
.