Air-Spaced Etalons

Air-spaced etalons have appropriate grade fused silica (UV-visible or IR) substrates. Outside-face AR coatings and wedges on the substrates prevent extraneous interference patterns from forming. Spacers, optically contacted to the substrates, determine the parallelism of the mirrored surfaces and the etalon’s free spectral range. Depending upon the application, the spacers can be fused silica or a low thermal expansion material such as ULE.