Commissioning the First Free Electron Laser Based on a Variable-Period Undulator

Variable period undulators (VPUs) have a number of advantages over conventional undulators, but until recently they have not been used in free electron lasers (FELs). In the summer of 2021, such an undulator was installed on the second track of the Novosibirsk free electron laser, and lasing in the spectral range of 15–120 μm was obtained. This article describes the design of this undulator and presents the results of measurements of the radiation parameters.