AUTHOR=Wang Wen-Wei , Chen Zhi-Ang , Zhang Han , Du Shize , Wu Rui , Qiao Chang , Kuang Shiyin , Zhang Xibo 

TITLE=Design and realization of a 3-K cryostat for a 10-cm ultrastable silicon cavity

JOURNAL=Frontiers in Physics

VOLUME=Volume 11 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2023.1176783

DOI=10.3389/fphy.2023.1176783

ISSN=2296-424X

ABSTRACT=Crystalline optical cavities operating at cryogenic temperatures provide a promising route for realizing the next generation of ultrastable lasers with extremely low thermal noise floor. However, it remains challenging to realize a closed-cycle cryostat for cooling a relatively long cavity to very low temperatures.
Here we report on the design and experimental realization of a cryostat operating continuously at 3.1~K for an ultrastable 10-cm silicon cavity. Based on a combination of active temperature control and passive thermal damping, we realize at 3.1~K a two-second temperature instability of $6\times 10^{-8}$~K for the cavity. By implementing separate supporting structures for the cryocooler and the sample chamber, we realize vibration control on the $1\times 10^{-7}g$ level at one second in each spatial direction, where $g$ is the gravitational acceleration. With all these features, our cryostat can support an ultrastable silicon cavity with instability near its fundamental thermal noise floor at averaging time of 1 to 50~s. With proper upgrading, our platform holds promise for realizing ultrastable lasers with $3\times 10^{-17}$ or better frequency stability, which will in turn enable numerous studies on precision metrology and quantum manybody physics.