Compound Refractive Lenses Research Articles

Cylindrical compound refractive x-ray lenses using plastic substrates

We have measured the intensity profile of x rays focused by compound refractive lenses (CRLs) fabricated using acrylic (Lucite) and polyethylene plastics. A linear array of closely spaced holes acts as multiple cylindrical lenses. The important parameters for this type of focusing are the focal length and absorption, and, for wavelengths shorter than 3 Å, low atomic number plastics are suitable. We have experimentally demonstrated that we can achieve one-dimensional focusing for photon energies between 9 and 19.5 keV with focal lengths between 20 and 100 cm. For example, using 12 keV x rays we have achieved focal full width at half maximum linewidths down to 21 μm at a distance of only 20 cm from the CRL. The x-ray source was a synchrotron emitter whose source size in the vertical dimension was 445 μm.

A microscope for hard x rays based on parabolic compound refractive lenses

We describe refractive x-ray lenses with a parabolic profile that are genuine imaging devices, similar to glass lenses for visible light. They open considerable possibilities in x-ray microscopy, tomography, microanalysis, and coherent scattering. Based on these lenses a microscope for hard x rays is described, that can operate in the range from 2 to 50 keV, allowing for magnifications up to 50. At present, it is possible to image an area of about 300 μm in diameter with a resolving power of 0.3 μm that can be increased to 0.1 μm. This microscope is especially suited for opaque samples, up to 1 cm in thickness, which do not tolerate sample preparation, like many biological and soil specimens.

A microcapillary lens for X-rays

A new design of a compound refractive lens for X-rays is proposed. The lens is made as a set of glue microlenses placed in a glass capillary. The technique of lens fabrication is described. Results of ray tracing calculations for 8 and 15 keV photons are represented.

Optimization of compound refractive lenses for X-rays

The theory of compound refractive lenses for the focusing of Synchrotron radiation X-ray beams is reviewed. The optimization of the transmission and minimization of the image size is discussed for both circular and parabolic holes. A comparison is made with ray tracing. The small-angle scattering expected from the surface roughness and the density fluctuation of the material is addressed. A successful comparison is made with the transmission and spot sizes measured on focusing lenses made of beryllium and Pyrocarbone between 20 and 30 keV on the ID6 undulator beamline of the ESRF. A rms spot size of 6.8 μm×100 μm has been recorded at a photon energy of 23.8 keV in a two plane focusing geometry. The peak spectral flux per unit surface in the focused beam is 26 times higher than that observed without lens. The expected transmission of such lenses placed at a distance of 24 m from an undulator or a bending magnet source point of the ESRF is given in the 1–100 keV energy range for focal length varying between 1 and 24 m. These lenses are inexpensive, very flexible and insensitive to heat load. They are particularly well suited to the undulator beamlines of the third generation sources in the 1–200 keV range. Future developments are discussed.

Focusing high-energy x rays by compound refractive lenses

Compound lenses made from low-Z materials (e.g., Be, B, C, and Al) set up as a linear array of refractive lenses are proposed for submicrometer focusing of high-energy x rays (>5 keV) in one or two dimensions. A theory of focusing based on Maxwell's equation and the Fresnel-Kirchhoff approach is presented. Compound refractive lenses were manufactured by drilling into an Al block a linear array of 200 closely spaced holes 0.5 mm in diameter for linear focusing and two crossed arrays of 100 holes each for point focusing. Focal spots of 3.7 mum and 8 mum x 18 mum were obtained at 30 keV for linear and two-dimensional lenses, respectively. Different technologies of manufacturing and possible applications of the proposed lenses are discussed.

Compound refractive optics for the imaging and focusing of low-energy neutrons

Low-energy neutrons are essential for the analysis and characterization of materials and magnetic structures. However, both continuous (reactor-based) and pulsed (spallation-based) sources of such neutrons suffer from low fluence. Steering and lensing devices could improve this situation dramatically, so increasing spatial resolution, detectable sample volume limits and even perhaps opening the way for the construction of a neutron microscope. Neutron optics have to date exploited either Bragg diffraction1,2, such as bent crystals, or reflection, as in mirror3 guides or a Kumakhov lens4,5. Refractive optics remain an attractive alternative as they would permit full use of the beam cross-section, allow a compact and linear installation and, because of similarity to conventional optics, enable the use of commercial design and simulation tools. These advantages notwithstanding, single-element refractive optics have previously been considered impractical as they are too weakly focusing, too absorptive and too dispersive. Inspired by the recent demonstration6 of a compound refractive lens (CRL) for high-energy X-rays, we have designed, built and tested a prototype CRL for 9–20-A neutrons by using readily available optical components: our CRL has gains greater than 15 and focal lengths of 1–6 m, well matched to small-angle neutron scattering.

A compound refractive lens for focusing high-energy X-rays

THE development of techniques for focusing X-rays has occupied physicists for more than a century. Refractive lenses, which are used extensively in visible-light optics, are generally considered inappropriate for focusing X-rays, because refraction effects are extremely small and absorption is strong. This has lead to the development of alternative approaches1,2 based on bent crystals and X-ray mirrors, Fresnel and Bragg–Fresnel zone plates, and capillary optics (Kumakhov lenses). Here we describe a simple procedure for fabricating refractive lenses that are effective for focusing of X-rays in the energy range 5–40 keV. The problems associated with absorption are minimized by fabricating the lenses from low-atomic-weight materials. Refraction of X-rays by one such lens is still extremely small, but a compound lens (consisting of tens or hundreds of individual lenses arranged in a linear array) can readily focus X-rays in one or two dimensions. We have fabricated a compound lens by drilling 30 closely spaced holes (each having a radius of 0.3 mm) in an aluminium block, and we demonstrate its effectiveness by focusing a 14-keV X-ray beam to a spot size of 8 μm.