On the duration of continuous operation of an optical frequency standard based on strontium atoms

This paper examines methods for increasing the duration of autonomous continuous operation of optical frequency standards. We have realised the secondary cooling of strontium atoms without using phase stabilisation during the formation of cooling and intermixing light beams and proposed a clock laser frequency stabilisation algorithm that compensates for the acoustic noise-induced laser frequency instability. Experiments have been performed using two distinct algorithms for laser frequency stabilisation to the frequency of an atomic transition. The maximum duration of continuous autonomous operation of the system was 25 000 to 50 000 s with one stabilisation algorithm and 70 000 to 200 000 s with the other algorithm.