On the emissivity of wire-grid polarizers for astronomical observations at mm-wavelengths

We have measured, using a custom setup, the emissivity of metallic wire-grids, suitable for polarimeters and interferometers at mm and far infrared wavelengths. We find that the effective emissivity of these devices is of the order of a few %, depending on fabrication technology and aging. We discuss their use in astronomical instruments, with special attention to Martin Puplett Interferometers in low-background applications, like astronomical observations of the Cosmic Microwave Background.