20 May 2011 Multilayer mirrors for FERMIatELETTRA beam transport system
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Abstract
Experiments performed in a Free Electron Laser (FEL) facility can require a selection of higher harmonics; a typical example is the pump and probe experiments in which the system under test is pumped with a fundamental wavelength and probed with its third harmonic. The wavelengths selection performed by a monochromator can affect beam properties such as wavefront deformation or time elongation and its usage in the beam manipulation should be avoided. Nevertheless, for a limited number of wavelengths, the selection can be performed using periodic multilayer coatings (MLs) with the reflectivity peak tuned at the desired harmonic: this technique is already foreseen at the new FERMI@Elettra FEL facility for selecting 20nm, 16nm, 13.5nm and 6.66nm harmonics. In order to improve the fundamental rejection, the MLs have been overcoated by different capping-layers; in particular at shortest wavelength higher rejection ratio have been obtained by the use of a third absorbent material in the capping layer. However, this same approach has not showed considerable improvements at the longest wavelengths, where interferential aperiodic capping-layers designed using a method based on the control of standing wave distribution are to be preferred.
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A. J. Corso, A. J. Corso, P. Zuppella, P. Zuppella, P. Nicolosi, P. Nicolosi, D. Cocco, D. Cocco, M. G. Pelizzo, M. G. Pelizzo, } "Multilayer mirrors for FERMIatELETTRA beam transport system", Proc. SPIE 8078, Advances in X-ray Free-Electron Lasers: Radiation Schemes, X-ray Optics, and Instrumentation, 80780F (20 May 2011); doi: 10.1117/12.886870; https://doi.org/10.1117/12.886870
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