HIGHER-ORDER SUPPRESSION IN DIFFRACTION-GRATING MONOCHROMATORS USING THIN-FILMS

Although a continuously tuneable source of photons is a Very desirable feature of synchrotron radiation it has one main drawback: the contam ination of the photon beam by higher-order diffracted light. Several e lements have absorption edges which lie between 10 and 200 eV, a range prone to high second-and third-order content in XW monochromators. Th ey can, therefore, be used as transmission filters to reduce this high er-order content. This paper describes the use of thin filters to redu ce the higher-order content in diffraction-grating monochromators. The ir suppression efficiency, transmission and ageing have been character ized using photoelectron spectroscopy and compared with calculated val ues. The effect of oxide contamination on their performance has been a ssessed. Filters are now installed on eight XUV beamlines and have bee n in routine use for several years.