An interferometric determination of the refractive part of optical constants for carbon and silver across soft X-ray absorption edges

Abstract : Interferometric, direct determinations of the f 1 scattering factor near absorption edges in the soft x-ray range is demonstrated. The interferometric system, which is based on wave front division (no beam splitter) with plane mirrors only, produces a linear fringe pattern. The principle consists in direct measuring of the fringe shift occurring upon insertion of a sample into one interferometer arm, by means of a dedicated detection system. This provides the optical thickness, which in turn gives the f 1 factor, knowing either the sample mass per unit surface, or the sample thickness and density. With the sample being probed in transmission under near normal incidence, the determination of f 1 is not perturbed by the absorption part of the complex scattering factor. Therefore, f 1 data obtained here can be said new and independent with respect to those obtained previously, in the sense that they are obtained from a new, purely experimental technique, and are neither deduced from nor perturbed by absorption. The interferometer design used can be implemented in a very large spectral range. For demonstrating the ability of this interferometric system to provide such new f 1 data, a thin free-standing carbon foil near the K edge (from 4.1 to 4.65 nm, 302-267 eV), and a membrane-supported silver layer near an M edge (from 2.6 to 3.8 nm, 477-326 eV) were used as test objects.
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Denis Joyeux, François Polack, Daniel Phalippou. An interferometric determination of the refractive part of optical constants for carbon and silver across soft X-ray absorption edges. Review of Scientific Instruments, American Institute of Physics, 1999, 70 (7), pp.2921-2926. ⟨hal-00867750⟩

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