The monochromator beamline at FLASH: performance, capabilities and upgrade plans

The monochromator beamline at the FLASH facility at DESY is the worldwide first XUV monochromator beamline operational on a free electron laser (FEL)source. Being a single-user machine, FLASH demands a high flexibility of the instrumentation to fulfil the needs of diverse experiments performed by a multidisciplinary user community. Thus, the beamline has not only been used for high-resolution spectroscopy that it was originally designed for, but also for pump-probe experiments controlling the temporal-spectral properties at moderate resolution, and as a filter for high harmonics of the FEL at very low resolution. The present performance and capabilities of the beamline are discussed with emphasis on particularities arising from the nature of the FEL source, and current developments are presented aiming to enhance its capabilities for accommodating a wide variety of experiments.