Interference Filters and Fabry-Perot Interferometers for the Far Infrared

Abstract

This paper describes measurements on transmission interference filters for the far infrared (100–800 μ region). The reflection layers of these filters are metallic mesh. The measured coefficients of finesse, ten to sixty, are comparable with the values which can be obtained for interference filters in other spectral regions. Peak-transmission values up to 0.9 were reached. From these measurements the absorptivity of the single grids has been determined. Measurements on a variable spacing interference filter showed that the finesse is proportional to the square of the wavelength in accordance with theoretical predictions for interference filters constructed with reflection layers of one-dimensional wire gratings.