Generation of ultrashort VUV and THz pulses at the DELTA storage ring

The optical klystron (two undulators, separated by a dispersive section) at DELTA, formerly operated as storage ring FEL, will be seeded with ultrashort pulses from a Ti:Sapphire laser. This will induce an energy modulation of the electron bunch in the first undulator, which is, after passing the dispersive chicane, converted to a density modulation. In the second undulator, the electrons will coherently emit ultrashort pulses at harmonics of the fundamental seeding wavelength. This process, called ''coherent harmonic generation'' (CHG), shall also be exploited in pump-probe measurements due to its natural synchronization with the seeding laser. Nonlinear frequency conversion techniques for the seeding laser allow for the generation of CHG pulses at different wavelengths. Additionally, coherent ultrashort THz pulses will be generated several meters downstream of the optical klystron by the laser-induced gap in the electron bunch. These will be extracted using a dedicated beamline. Unlike the first CHG experiments at other facilities, the project at DELTA aims at the application of CHG during standard user operation and hence will deliver stable and reliable radiation for user experiments.