Index of refraction determination in the near-mm wavelength range using a mesh Fabry-Perot resonant cavity

A plane-parallel mesh Fabry-Perot resonant cavity has been used to determine the indices of refraction of a number of low-loss materials at 245.351 GHz using a C13H3F far-IR laser. The necessary apparatus is readily available in many far-IR laser laboratories and is readily extendable to other laser and millimeter-wave source frequencies. The values were compared to the measurements of other researchers at neighboring frequencies as available.