The Fabry-Perot etalon is a versatile device but it is not widely used because of the high cost of its components if purchased from a commercial supplier. The author has developed a method of making spacers of excellent quality for a large diameter (60 mm) etalon for less than 10% of the typical price quoted by specialty houses which make them to order. While the spacers described in this paper were made for use with the finest quality flats obtainable, the fact that 25.4-mm-diam, 1/20 wavelength, optical flats are available for less than $100.00 per pair, means that a Fabry-Perot etalon is now within the reach of even the most impecunious physics department. Such an etalon can always be up-graded by purchasing better-quality flats; no additional work on the spacers would be required.
F. M. PHELPS, III, "Making of Spacers for Fabry-Perot Etalons," J. Opt. Soc. Am. 55, 293-294 (1965)