Upgrade plans for the intense THz source and beamline at the soft X-ray free electron laser FLASH

As part of the project of upgrading FLASH, the soft X-ray free electron laser (FEL) at DESY in Hamburg, into a seeded FEL, the intense undulator-based THz source will be geometrically separated from the XUV FEL. This allows the THz beamline to operate fully in parallel and largely independent of the XUV FEL, while the beamline transmission will be enhanced for frequencies higher than 6THz. In a newly designed semi-permanent endstation, the XUV beam (approx. 4-60nm), the intense THz beam (1-30THz) and a pump-probe laser (200nm to 1.25$\mu$m) can be combined to study solid state- and surface physics at ultra-short time scales, such as femto-magnetism. The upgrade is planned to be ready for users from 2025.