Interferometric techniques for measuring dimensional stability of passive etalons.

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 10(8). The precision of the measurements defined as L/DeltaL when DeltaL is the smallest detectable change in the optical length L is also of this order.