Single-mode power scaling in a multi-beam photonic free-electron laser

Multi-beam slow-wave devices, such as photonic free-electron lasers (pFEL), are promising for power up-scaling of THz sources. However, multi-beam concepts usually require wide and hence overmoded slow-wave structures. This could lead to undesired multimode output. Here, we present single-mode power up-scaling of a pFEL when increasing the electron beam number.