First Lasing of FLASH2 at DESY

The free-electron laser FLASH at DESY in Hamburg, Germany, has been extended by a second undulator line in a separate tunnel and a new experimental hall (Figure 1). The existing undulator line, called FLASH1, and the new one, which includes provisions for external seeding to be realized later, called FLASH2, both use the same linear accelerator. They are operated in tandem by separating the pulse train into two sections, which are then directed to the different undulators. The linac energy is determined by the needs of the experiments at FLASH1, whereas the wavelength at FLASH2 can be varied in the limits of the tuning range of the undulators.