Compound refractive lenses (CRLs) are arrays of concave lenslets used to focus X-rays. For a given incident X-ray
beam energy, the focal length of a CRL depends on the material and shape of the individual lenslets, and in particular is
inversely related to the number of lenslets in the array. The throughput of a lens array is heavily affected by absorption
of the X-rays in the lens. For this reason, it is necessary to employ low-atomic-number materials and fabricate the
lenses as thin as possible, especially for low to moderate X-ray energy range (~ 5 - 20 keV) photons.
Lithium and beryllium are two of the best candidate materials for X-ray lenses due to their relatively high (real
decrement) index of refraction and low X-ray absorption. Lithium is very malleable, however, and reacts strongly with
moisture in the air, requiring a special fabrication environment and housing. Beryllium, on the other hand, is a solid
metal and is easy to machine and handle.
This paper summarizes the recent work at the Advanced Photon Source (APS) on parabolic lithium and cylindrical
beryllium lenses. These lenses have been tested on APS X-ray beamlines. Their performance in terms of the focal size
and gain is described and further improvements including tighter manufacturing tolerances and thinner lens walls are
Compound refractive lenses (CRLs) are arrays of lenses designed to focus x-rays. The advantage of a focused x-ray beam is improvement in imaging resolution for applications such as microscopy and tomography. CRLs are desirable due to their simple designs and ease in implementation and alignment. One method of fabricating CRLs is extrusion. Extrusion can be employed to produce, for example, aluminum CRLs for high-energy applications because many aluminum products are produced in this manner. Multiple lenses can be extruded in an array in a single run. This method is relatively cost effective compared to others methods of fabricating CRLs. Two generations of extruded aluminum CRLs have been manufactured to date with lens wall thicknesses of 200 and 100 μm, respectively. The first-generation CRL yielded focusing and established the potential to produce high gain if reduced wall thicknesses could be achieved. Testing of the second generation is reported here.