Effective aperture of X‐ray compound refractive lenses. (12th April 2017)

• Record Type: Journal Article
• Authors: Kohn, V. G.
• Is Part Of: Journal of synchrotron radiation. Volume 24:Part 3(2017)
• Page Start: 609
• Page End: 614
• Publication Date: 2017-04-12
• Subjects: X‐ray focusing theory -- compound refractive lens -- effective aperture -- X‐ray absorption -- computer simulations; Synchrotron radiation -- Periodicals; Free electron lasers -- Periodicals; 539.73505
• DOI: 10.1107/S1600577517005318
• Languages: English
• ISSNs: 0909-0495

Abstract

Abstract : A new definition of the effective aperture of the X‐ray compound refractive lens is proposed. Abstract : A new definition of the effective aperture of the X‐ray compound refractive lens (CRL) is proposed. Both linear (one‐dimensional) and circular (two‐dimensional) CRLs are considered. It is shown that for a strongly absorbing CRL the real aperture does not influence the focusing properties and the effective aperture is determined by absorption. However, there are three ways to determine the effective aperture in terms of transparent CRLs. In the papers by Kohn [(2002). JETP Lett. 76, 600–603; (2003). J. Exp. Theor. Phys. 97, 204–215; (2009). J. Surface Investig. 3, 358–364; (2012). J. Synchrotron Rad. 19, 84–92; Kohn et al. (2003). Opt. Commun. 216, 247–260; (2003). J. Phys. IV Fr, 104, 217–220], the FWHM of the X‐ray beam intensity just behind the CRL was used. In the papers by Lengeler et al. [(1999). J. Synchrotron Rad. 6, 1153–1167; (1998). J. Appl. Phys. 84, 5855–5861], the maximum intensity value at the focus was used. Numerically, these two definitions differ by 50%. The new definition is based on the integral intensity of the beam behind the CRL over the real aperture. The integral intensity is the most physical value and is independent of distance. The new definition gives a value that is greater than that of the Kohn definition by 6% and less than that of the Lengeler definition by 41%. A new approximation for the aperture function of a two‐dimensional CRL is proposed which allows one to calculate the two‐dimensional CRL through the one‐dimensional CRL and to obtain an analytical solution for a complex system of many CRLs.