Double gratings and their applications as Fabry-Perot interferometers

A rigorous theoretical formalism describing the diffraction of a P polarised plane wave by a perfectly conducting double grating is presented. The use of such structures as long wavelength Fabry-Perot interferometers is investigated and the individual effects of the design parameters are determined. In particular, it is shown that the finesse of the interferometer is influenced by both the mark-space ratio and the groove depth, whereas the position of the resonance maxima are dictated almost entirely by the mark-space ratio.