Phase locking of a $D_2O$ laser to a frequency standard

An oscillator chain phase-locked to a primary frequency standard was developed: this chain included $D_2O$ and $HCN$ lasers, as well as klystrons emitting in the millimeter and centimeter ranges. Phase locking to a frequency standard of wavelength shorter than 100 $\mu m$ was achieved for the first time. The error of tracking of the standard frequency by the frequency of the $D_2O$ laser did not exceed $3\cdot10^{-13}$ and the nominal frequency of this laser was 3557147500000 Hz. This laser was used to measure the frequency of a $CO_2/OsO_4$ laser with an error of $\thicksim3\cdot10^{-11}$ and this error was due to the frequency instability of the $CO_2/OsO_4$ laser. It should be possible to improve the precision of these measurements by two orders of magnitude.