A description is given of a Fabry-Perot interferometer whose plates are maintained automatically parallel independently of their separation. Errors in the spacing of the plates due to lack of parallelism nowhere exceed the errors in the flatness of the plates themselves. The mounting of piezoelectric barium titanate ceramics to achieve rapid scanning rates is discussed.
J. V. Ramsay, "A Rapid-Scanning Fabry-Perot Interferometer with Automatic Parallelism Control," Appl. Opt. 1, 411-413 (1962)