Characterization of dimensional stability for materials used in ultra-stable structures

Modern observatories including ultra-stable spectrographs, optical telescopes and gravitational wave observatories rely on ultra-stable structures to meet their science objectives. These structures must exhibit pm to nm level length stability over a few seconds to a few hours and mu m-level length stability over mission duration of several years in some cases. The use of ultra-low CTE glass substrates provide the required stability while being highly fragile, having limited adaptability while driving turnaround times longer. We characterized structures made using materials that can provide the required stability while improving on the adaptability, turnaround times, structural mass and strength. These include a compound structure made using ALLVAR Alloy, a metal with a negative CTE, a second structure made of HB-Cesic, a full-ULE structure and a metal-ULE hybrid structure. In this work, we present a comparative analysis of the measured length noise and the long-term length stability for these structures.