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8 October 2014 Time-delay-compensated grating monochromator for FEL beamlines
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We present the design of a time-delay-compensated monochromator explicitly designed for extreme-ultraviolet FEL sources, in particular the upcoming FLASH II at DESY (Hamburg). The design originates from the variable-line-spaced (VLS) grating monochromator by adding a second grating to compensate for the pulse-front tilt given by the first grating after the diffraction. The covered spectral range is 6-60 nm, the spectral resolution is in the range 1000–2000, while the residual temporal broadening is lower than 15 fs. Accounting for typical FLASH II divergences, the grazing angles on the different optics have been chosen so that the mirrors and gratings are respectively shorter than 500 mm and 300 mm. The proposed design: 1) minimizes the number of optical elements, since just one grating is added with respect to a standard VLS monochromator B-L; 2) guarantees high focusing properties in the whole spectral range of operation; 3) requires simple mechanical movements, since only rotations are needed to perform the spectral scan.
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Fabio Frassetto, Elke Ploenjes, Marion Kuhlmann, and Luca Poletto "Time-delay-compensated grating monochromator for FEL beamlines", Proc. SPIE 9210, X-Ray Free-Electron Lasers: Beam Diagnostics, Beamline Instrumentation, and Applications II, 92100I (8 October 2014);

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