Smith–Purcell effect

The Smith–Purcell effect is a phenomenon that occurs when a charged particle, such as an electron, moves past a periodic structure, such as a grating or series of slits. As the charged particle travels at a speed comparable to the speed of light, it can generate electromagnetic radiation at specific wavelengths. This effect arises from the interaction between the moving charge and the periodic structure, which causes the radiation to be emitted in a direction that depends on the geometry of the setup.