Infrared Response of a Quasi-Crystalline Filter

There is an abundance of infrared radiation throughout the universe, which presents a challenge when studying the cosmic microwave background and other astronomical objects. In order for our team to study the cosmic microwave background polarization, the detectors need to be kept at approximately 0.1 Kelvin, and, if present, will warm the instrument. This thermal radiation can be mitigated by using an infrared filter. Traditionally, infrared metal mesh filters consist of several layers of a translationally symmetric tiling of squares are used to block radiation in large apertures. This approach can lead to diffraction at large angles, which, if present, can also create a pattern in the angular response. This decreases the angular resolution and beam symmetry, which is vital for polarimetry measurements. The main goal of this project was to design a filter with a different geometric tiling approach that has the potential to decrease diffraction at large angles. Instead of using a square tiling, this study uses a rotationally symmetric, tilling of pentagons. The resulting tiling is referred to as a non-periodic quasi crystal, meaning that it cannot be tiled in two dimensional translational space. In order to better understand the optical behavior of the quasi-crystalline tiling, a simplified version of the filter was primarily studied due to computational restrictions. The quasi-crystalline filter has been fully designed and is awaiting fabrication.