A fully crystalline ultra-stable optical reference cavity​​*

State-of-the-art neutral atom clocks employing ultra-stable reference Fabry-Perot cavities push the frontiers of precision measurements and metrology [1], [2]. To date, the ultra-stable reference cavity frequency stability record is set by a 21-cm silicon cavity operating at 124 K with 4 × 10-17 stability at 1 to 103 s averaging time, limited by coating Brownian noise floor [3]. This coating-limited stability performance motivates the search for novel coating materials with lower thermal noise floors [4]. In this talk/poster, we’ll present the current frequency stability performance of a 6-cm silicon cavity with crystalline coating operating at 16 K [5]. Comparison with a strontium atomic clock allows characterizations of the cavity’s long-term frequency stability. The improved performance opens up possibilities of robust operations of optical atomic clocks and makes timekeeping with all optical technology a promising prospect [6].