Monochromator beamline for FLASH

Abstract

The design of a high resolution monochromator for the vacuum ultraviolet free electron laser at Hamburg (FLASH), DESY, is described. The monochromator is constructed as a plane grating monochromator using collimated light. Modifications have been made to take into account the free electron laser (FEL) beam characteristics, in particular, the extremely high peak power density of the radiation. Ray tracing simulations yield a resolving power in the range of 10 000–70 000 depending on the photon energy and the grating in use. Our monochromator is equipped with a 200line∕mm grating for the energy range of 20–200eV—the operation regime of FLASH—and a high resolution 1200line∕mm grating for the energy range of 100–600eV, covering the higher harmonic radiation of the FEL.