The FLASH pump–probe laser system: Setup, characterization and optical beamlines

We describe the optical pump–probe laser system at the XUV free-electron laser FLASH at DESY. A growing interest in optical laser pulses combined with the free-electron laser (FEL) beam for time-resolved experiments raise high demands on the stability of operation and knowledge on the status of synchronization between the XUV and optical pulses. In this publication we describe this system, the characterization of the optical pulses, synchronization and timing schemes as well as beamlines that transport beam to experimental stations.