Chapter 9: Fabry–Perot cavities and Gaussian beams

Fabry–Perot cavities are ubiquitous in advanced interferometric gravitational-wave detectors. Among their applications, they are used to enhance the gravitational-wave signal, to filter laser noises and to remove unwanted spatial modes from the detector’s output. The goal of this chapter is to provide a description of the properties of Fabry–Perot cavities in the context of a gravitational-wave detector and an introduction to Gaussian beams.