Characterization of the long-term dimensional stability of a NEXCERA block using the optical resonator technique

NEXCERA is a machinable and highly polishable ceramic with attractive properties for use in precision instruments, in particular because its coefficient of thermal expansion exhibits a zero crossing at room temperature. We performed an accurate measurement of the long-term drift of the length of a 12~cm long NEXCERA block by using it as a spacer of a high-finesse optical cavity. At room temperature, we found a fractional length drift rate $L^{-1}d\Delta L/dt=-1.74\times10^{-8}~\mathrm{yr}^{-1}$.