Optical performance of materials for X-ray refractive optics in the energy range 8–100 keV

Abstract

A quantitative analysis of the crucial characteristics of currently used and promising materials for X-ray refractive optics is performed in the extended energy range 8-100 keV. According to the examined parameters, beryllium is the material of choice for X-ray compound refractive lenses (CRLs) in the energy range 8-25 keV. At higher energies the use of CRLs made of diamond and the cubic phase of boron nitride (c-BN) is beneficial. It was demonstrated that the presence of the elements of the fourth (or higher) period has a fatal effect on the functional X-ray properties even if low-Z elements dominate in the compound, like in YB. Macroscopic properties are discussed: much higher melting points and thermal conductivities of C and c-BN enable them to be used at the new generation of synchrotron radiation sources and X-ray free-electron lasers. The role of crystal and internal structure is discussed: materials with high density are preferable for refractive applications while less dense phases are suitable for X-ray windows. Single-crystal or amorphous glass-like materials based on Li, Be, B or C that are free of diffuse scattering from grain boundaries, voids and inclusions are the best candidates for applications of highly coherent X-ray beams.

Polished diamond X-ray lenses

“…As noted by Serebrennikov et al (2016), diamond lenses are the material of choice for X-ray lenses at higher X-ray energies, i.e. above 30 keV, when the advantage of higher transmission and larger effective aperture of Be lenses decreases.…”

“…Diamond is an excellent material for X-ray optics (Shvyd'ko et al, 2017) as it can withstand high heat loads due to its unrivalled thermal conductivity, absorbs little due to its low atomic number (Z = 6), can be obtained in pure and crystalline form with reasonable quality, and, as a refractive element such as a focusing lens, offers a refraction-to-absorption ratio / (Serebrennikov et al, 2016) higher than all typical lens materials except for Be. Since the advent of X-ray focusing lenses (Tomie, 1997;Snigirev et al, 1996), significant effort has been put into the fabrication of diamond X-ray lenses.…”

Feasibility Analysis of Sapphire Compound Refractive Lenses for Advanced X-Ray Light Sources

“…where δ is the refractive indices, which is positively related to the atomic number and density. And β is the absorption coefficient, which is also positively related to the atomic number and density [7,19]. In the process of using the lens, it is hoped that the refraction effect of the material is good and the absorption is small.…”

Modelling phase imperfections in compound refractive lenses

“…The same is valid for the cases where the distance between them can be ignored. Typical materials used for X-ray lenses have 10 −7 ≤ δ ≤ 10 −3 for their usual application energies (Serebrennikov et al, 2016). To overcome the weak refraction of a single element, several X-ray lenses are stacked (Tomie, 1994;Snigirev et al, 1996).…”

“…3(b). This can be justified by the fact that at their typical operation energy, the materials used for lens manufacturing have a very low δ (Serebrennikov et al, 2016), rendering the individual lenslets a weak focusing element where the projection approximation holds (Protopopov & Valiev, 1998). The complex transmission representation of a CRL based on the MS approach is given by:…”