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20 May 2011 Multilayer mirrors for FERMIatELETTRA beam transport system
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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.
© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A. J. Corso, P. Zuppella, P. Nicolosi, D. Cocco, and 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);

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