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.

► We measured the emissivity of metal wire-grids at 150 GHz using a custom setup.
► This is a few %, larger than the emissivity of typical mirrors at 150 GHz.
► This dominates the background in room-temperature interferometers and polarimeters.