Jastrow, U.
(U. Jastrow)

TUPOS13 On-Line Spectral Monitoring of the VUV FEL Beam at DESY
Piergiorgio Nicolosi, Maria-Guglielmina Pelizzo, Luca Poletto (INFM-LUXOR, Padova), Joseph Feldhaus, Ulrich Hahn, U. Jastrow, Elke Ploenjes, Kai Tiedtke (DESY, Hamburg)

A grazing-incidence flat-field spectrometer has been designed. The optical design is based on a Kirkpatrick-Baez configuration in which one of the optical elements is a spherical mirror and the other is a spherical grating [1]. This configuration gives high spectral and spatial resolution even for a large field-of-view. The grating is a variable-line-spaced one, in which the groove spacing changes along the surface following a polynomial law in order to obtain a flat-field focal surface nearly parallel to the grating normal. The detector can be both an EUV-enhanced CCD and a MCP-based detector. The spectrometer was tested in the 5-45 nm spectral region with spectra emitted both by a laser-produced-plasma and by a hollow-cathode lamp. Spectral resolution of about 2000 was measured at 20 nm, in good agreement with the theoretical predictions. Spatial resolution better than 0.1 mm over 2 mm field-of-view has been measured. At present, the instrument is installed at DESY (Hamburg, Germany) on the TESLA-Test-Facility and will be used for the monitoring of the spectral emission of the FEL radiation in the 25-45 nm spectral region.