Metal Mesh Interference Filters for the Far Infrared

Abstract

Far ir Fabry-Perot type interference filters consisting of two parallel, closely spaced metal meshes have been reported by others. Using improved techniques, filters of this type have been fabricated with larger finesse and peak transmittance. Measured transmittance curves, obtained with the Aerospace lamellar grating interferometer have led to transmittance peaks whose sharpness appears to be limited principally by the beam convergence angle within the instrument (8 degrees ). From the measured peaks, finesses as large as 100 are obtained. Available mesh materials permit the construction of filters for any frequency from 10 cm(-1) (or lower) to at least 200 cm(-1). These will require absorbing components to eliminate unwanted harmonics.