Transportable single-crystal silicon ultra-stable cavity toward space applications

Abstract

Ultra-stable lasers with extremely low-frequency noise are essential for space-based precision metrology. Transportable single-crystal silicon optical reference cavities offer lower thermal noise floors in compact volumes, making them ideal candidates for ultra-stable lasers deployed in space. However, achieving low vibration sensitivity in transportable designs remains challenging due to the anisotropic mechanical properties of silicon. In this work, we present a finite element method (FEM) optimized design for transportable single-crystal silicon cavities, featuring a 112.5 mm long spacer supported by an Invar six-point mounting frame, and a predicted thermal noise floor of 8.9×10 −17 . The assembly successfully withstood in-vehicle transportation and cryogenic thermal cycling tests. Moreover, we have established an ultra-stable laser system based on the cavity operating at 124 K, experimentally measured its total vibration sensitivity of 4.9(1)×10 −10 /g, and estimated the fractional frequency instability of 4×10 −16 for averaging times ranging from 0.5 to 100 s. These results demonstrate that our cavity design takes the first step in the way for future ultra-stable lasers for space-based precision metrology and fundamental physics experiments.