Knowledge Bank

Measurements and $theory1$ have shown that metal wire gratings have reflectivity, transmissivity, and small absorptivity for radiation with the electric vector parallel to the wires at wavelengths longer than the grating constant. In contrast to the parallel polarization, the transmission is high for perpendicular polarization. A rectangular mesh does not have the polarization characteristic but has low loss transmission and reflection characteristics like the parallel case. The wavelength dependence is determined, in the main, by the wire spacing and the ratio of wire spacing to wire diameter. The measured transmission of a metal mesh of fifty micron spacing is shown for the 40-300 microns wavelength region. Such mesh has a high reflectivity and low loss in the long wavelength region and therefore is desirable for use in a Fabry-Perot etalon. Several types of etalons have been constructed. Typical experimental evaluation for first order at 250 microns: transmission band half width is one-thirtieth of central wavelength; maximum transmission is seventy percent.