Frequency combs for precision synthesis and characterization of optical atomic standards

Over the past 20 years, optical frequency combs with atomic clocks, have been a powerful and enabling technology in the context of time and frequency measurement. Impressively, optical atomic clocks have yielded a 100 million-fold improvement in uncertainty in the past 30 years. These improvements are fueling a push toward redefinition of the SI second to optical atomic references, as well as application of atomic clocks to tests of fundamental physics and as relativistic gravitational sensors. Unfortunately, the long times needed to average down clock quantum projection noise and laser noise to reach a measurement stability at and beyond the 10 −18 level limit the feasibility of next-generation applications. Here I describe the measurement advances in clock comparisons enabled by optical frequency combs and how differential measurement can improve the measurement stability. This paper will also include a discussion of optical frequency combs and their application to precision time/frequency metrology.