Fabrication of Compound Refractive X-ray Lenses Using LIGA Process and Performance Tests

Abstract

Recent advances of X‐ray microscopy technology enable the visualization of some micro/nano‐scale objects which optical microscopy and electron microscopy cannot be used to observe. The X‐ray microscopy can be applied to observe the internal structure of a thicker sample than the electron microscopy can, and its spatial resolution is higher than that of the optical microscopy. Moreover, it has a powerful element specific imaging ability. For further improving the X‐ray microscope, it is indispensable to make X‐ray optics for focusing X‐rays more effectively. Recently, various X‐ray lenses such as diffraction lenses of FZP(Fresnel zone plate) and spatter‐sliced FZT, total reflection lenses of K‐B(Kirkpatrick‐Baez) mirror and Wolter mirror, and refractive lens of CRL(compound refractive lens) were introduced. Compared with the other types of lenses, CRL is easy to fabricate and handle. In this study, we designed and fabricated various types of CRLs using LIGA(LIthographie, Galvanoformung, Abformtechnik) process, and used PMMA(Poly(methyl methacrylate)) material as the material of CRL. Their performances are tested with varying parameters such as parabolic/kinoform shape, radius of curvature, wall thickness between adjacent lenses, and width of lenses. The performance tests were carried out by using a simple synchrotron X‐ray imaging method. The tests results revealed that hard x‐rays could be condensed well by the CRL of PMMA material at the focal point we expect We captured sample images one‐dimensionally magnified by CRLs. Furthermore, we found which parameter is more effective for enhancing focus efficiency and which parameter should be considered more carefully in the fabrication process of LIGA.