Spatial filtering of structured light

Abstract: Spatial filtering is a commonly deployed technique to improve the quality of laser beams by optically filtering the noise. In the "textbook" example, the noise is usually assumed to be high frequency and the laser beam, Gaussian. In this case, the filtering is achieved by a simple pin-hole placed at the common focal plane of two lenses. Here, we explain how to generalize the concept of spatial filtering to arbitrary beam profiles: spatial filtering of structured light. We show how to construct the spatial filters using a range of structured light examples, and highlight under what conditions spatial filtering works. In the process, we address some misconceptions in the community as to how and when spatial filters can be applied, extend the concept of spatial filtering to arbitrary beam types and provide a theoretical and experimental framework for further study at both the undergraduate and graduate level.