T-ray multilayer interference filter

An optical multilayer interference filter is made from two or more different dielectric materials layered in such a way that it promotes constructive/destructive wave interference for a selected frequency in the direction normal to the layers. Usually, each layer has the thickness of a quarter of wavelength at which the stopband is required. In this paper, a quarter-wave interference filter is realised for T-ray applications. The dielectric materials used are high-resistivity silicon and free space, both of which have high transparency to T-rays and flat responses over the frequencies of interest. The designed thickness of both materials is in the order of a hundred microns. The THz-TDS measurement of the finished structure is in agreement with theory.