A Free Electron Laser (FEL) is a type of laser that generates high-intensity light by using free electrons instead of atoms or molecules. In an FEL, a beam of electrons is accelerated and then passed through a magnetic structure called an undulator. As the electrons move through this undulator, they emit coherent light, which can be tuned across a wide range of wavelengths, from infrared to X-rays. FELs are unique because they do not rely on a specific material to produce light, allowing for greater flexibility in applications. They are used in various fields, including materials science, biology, and medicine, to study the properties of matter at the atomic level and to develop new technologies.