Status of sFLASH, the Seeding Experiment at FLASH

Recently, the Free electron LASer in Hamburg FLASH at DESY has been upgraded considerably [1]. Besides increasing the maximum energy to about 1.2 GeV and installation of a third harmonic rf cavity linearizing the longitudinal phase space distribution of the electron bunch, an FEL seeding experiment at wavelengths of about 35 nm has been installed. The goal is to establish direct FEL seeding employing coherent VUV pulses produced from a powerful drive laser by high harmonic generation HHG in a gas cell. The project, called sFLASH, includes generation of the required HHG pulses, transporting them to the undulator entrance of a newly installed FEL amplifier, controlling spatial, temporal and energy overlap with the electron bunches and setting up a pump probe pilot experiment. Sophisticated diagnostics is installed to characterize both HHG and seeded FEL pulses, both in time and frequency domain. Compared to SASE FEL pulses, almost perfect longitudinal coherence and improved synchronization possibilities for the user experiments are expected. In this paper the status of the experiment is presente