Abstract
A novel and economical approach for fabricating compound refractive lenses for the purpose of focusing hard X-rays is described. A silicon master was manufactured by UV-lithography and deep reactive ion etching (DRIE). Sacrificial structures were utilized, which enabled accurate control of the etching profile and were removed after DRIE. By electroplating, an inverse nickel sample was obtained, which was used as a mold insert in a commercial polymer injection molding machine. A prototype lens made of polyethylene with a focal length of 350 mm was tested using synchrotron radiation at photon energies of 17 keV. A 55 µm long line focus with a minimal waist of 770 nm (FWHM) and a total lens transmittance of 32% were measured. Due to its suitability for cheap mass production, this highly efficient optics may find widespread use in hard X-ray instruments.
Highlights
Refractive X-ray lenses are versatile optical components in synchrotron beamlines and act e.g. as condensers or objectives in hard X-ray microscopes [1,2]
A silicon master was manufactured by UV-lithography and deep reactive ion etching (DRIE)
An inverse nickel sample was obtained, which was used as a mold insert in a commercial polymer injection molding machine
Summary
Refractive X-ray lenses are versatile optical components in synchrotron beamlines and act e.g. as condensers or objectives in hard X-ray microscopes [1,2]. Polymeric multi-prism lenses were molded from anisotropically etched silicon masters [18,19] or structured by laser ablation [20] These optics face technological challenges when sub-micron focusing is required [21]. DRIE was a critical process step in ensuring the near-90° sidewalls required to guarantee both lens uniformity and the successful release of the polymeric part from the mold To this end, we utilized sacrificial structures, which facilitated accurate profile control [23]. Due to the slightly tapered sidewall, R varied by ± 2% along the 200 μm deep structure We accepted this minor deviation from an ideal cylindrically parabolic shape for the first demonstration of the injection molded polymeric lenses. A shim was cut from the wafer by laser micro machining and inserted into the tool of an ENGEL Victory Tech injection molding machine
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