Dimensional Stability of Fused Silica, Invar, and Several Ultra-low Thermal Expansion Materials

We have measured length change vs time for several low thermal expansion materials maintained in evacuated environments at constant temperature (near 300 K). Materials were two types of fused silica, Cer-Vit, ULE, Zerodur, Invar, and super Invar. Δ L/L was measured over a period of 170 days to a precision of two to three parts in 10 9 . In addition, we have measured time-dependent changes in optical contact interfaces and have placed an upper limit on drift of optical phase shift on reflection from multilayer dielectric coatings.