The last lens is cut to indicate the structure of a single CRL. Intensity and coherence properties of the focused radiation are considered. Partially coherent radiation is generated in the undulator and is focused by a stack of CRLs. Our results can be naturally generalized to other types of focusing elements such as Fresnel zone plates. In this paper we describe the propagation of partially coherent X-ray radiation through such a focusing system and determine its size and coherence properties at any position downstream from the CRL. Synchrotron radiation is generated in the undulator and a focusing element consisting of a stack of CRLs focuses the beam. A typical focusing scheme is shown in Fig. Nowadays several techniques to focus X-ray beams at third- and fourth-generation sources are used, such as Kirkpatrick–Baez (KB) mirrors (Mimura et al., 2010 ), Fresnel zone plates (Sakdinawat & Attwood, 2010 ), bent crystals in Bragg geometry (Zhu et al., 2012 ) and compound refractive lenses (CRLs) (Snigirev et al., 1996 Schroer et al., 2003 ). These can be achieved by an effective use of focusing elements. A detailed knowledge of the coherence properties can even be used to improve the resolution obtained in the CXDI phase retrieval (Whitehead et al., 2009 ).įor scientific applications at the nanoscale, beam sizes from tens to hundreds of nanometers with high flux densities are required. As such, spatial coherence across the sample is essential and understanding the coherence properties of the incoming X-ray beams generated at new generation synchrotron sources is of vital importance for the scientific community. The key feature of all coherence-based methods is the interference of the field scattered by different parts of the sample. In CXDI static real space images of the sample are obtained by phase retrieval techniques (Fienup, 1982 ), whereas in XPCS dynamics of a system are explored by correlation techniques (Goodman, 2007 ). Most prominent among these techniques are coherent X-ray diffractive imaging (CXDI) (Vartanyants et al., 2010 Chapman & Nugent, 2010 Mancuso et al., 2010 Vartanyants & Yefanov, 2013 ) and X-ray photon correlation spectroscopy (XPCS) (Grübel & Zontone, 2004 ). The construction of these sources initiated developments of new research areas, which utilize partial coherence of the X-ray radiation. While ultimate storage rings, being diffraction-limited X-ray sources, are still under development (Bei et al., 2010 ), present third-generation synchrotrons are partially coherent sources (Vartanyants & Singer, 2010 ).
0 Comments
Leave a Reply. |