Infrared Response of a Quasi-Crystalline Filter*

The cosmic microwave background (CMB) is the left over radiation from the Big Bang. Studying this faint microwave signature gives insight into the conditions of the early universe. In order to make precision measurements of the CMB polarization, cryogenic detectors maintained at ~0.1 Kelvin are needed to operate the detectors. Background infrared radiation can warm the instrument and degrade its performance. This thermal radiation can be mitigated by using a series of infrared blocking filters. Traditionally, infrared metal mesh filters consist of several layers of a translationally symmetric tiling (e.g. squares or hexagons) are used to block radiation in large apertures. This approach can lead to diffraction at large angles, which can create a pattern in the angular response. This decreases the angular resolution and beam symmetry, which is vital for polarimetry measurements. This study uses a rotationally symmetric tilling of pentagons which cannot be tiled in two dimensional translational space, also known as a non-periodic quasi-crystal. The quasi-crystalline filter has been fully designed and is awaiting fabrication.