Methods are described for investigating the dimensional stability of passive Fabry-Perot etalons with spacers made of low expansion materials. The measurements are made in terms of the Krypton 86 primary length standard which is reproducible to 1 part in 108. The precision of the measurements defined as L/ΔL when ΔL is the smallest detectable change in the optical length L is also of this order.
C. F. Bruce and R. M. Duffy, "Interferometric Techniques for Measuring Dimensional Stability of Passive Etalons," Appl. Opt. 9, 743-747 (1970)