Far-infrared dichroic bandpass filters

Certain applications of far-IR photometry to plasma diagnostics and astrophysics require the simultaneous measurement of transient phenomena in one region of space at several frequencies. Inductive cross metal mesh is presently used as a reflective coating on solid dielectric Fabry-Perot etalons, in order to yield dichroic filters whose quality factors are in the 3-10 range. These filters, which reflect strongly in the frequencies below the bandpass while retaining that bandpass at incidence angles as large as 45 deg, have been used to make an efficient, far-IR dichroic photometer with six frequency bands between 10 and 100/cm wavelengths.