The FPI 100 is a confocal, scanning Fabry-Perot interferometer with a built-in photodetector unit, designed for measuring and controlling the mode profiles of continuous wave (cw) lasers. The FPI is available with different mirror sets and photodetectors for wavelength ranges between 330 nm and 3000 nm. The standard mirror reflectivity is 99.8 %, corresponding to a typical finesse of > 400, resolving even narrow laser lines.