Fabrication and performance of a lithium X-ray lens

Compound refractive lenses (CRLs) are arrays of concave lenses whose simple design and case in implementation and alignment make them an attractive optic to focus x-rays. Factors considered in designing CRLs include lens material, fabrication, and assembly. Lithium is a desirable material because it provides the largest index of refraction decrement per unit absorption length of any solid elements. Lithium is a difficult material to handle and fabricate because it is rather malleable and more importantly, it reacts with moisture, and to a lesser extent, with oxygen and nitrogen in air. It also tends to adhere to molds and dies. We report on the fabrication and performance of a parabolic lithium lens consisting of 32 lenslets. Lenslets are fabricated in a precision press using an indenter with a parabolic profile and a 100 mu m tip radius. The indenter is made of stainless steel and is figured using a computer numerically controlled (CNC) machine. The lens is designed to have a 1.7 in focal length at 10 keV energy. In an experiment conducted at the Advanced Photon Source (APS), a 0.5 mm x 0.5 mm monochromatic undulator beam strikes the lens. A focal length of 1.71, a focal spot size of 24 mu m x 34 mu m, and a peak intensity gain of over 18 are obtained.