Imaging properties of a spherical compound refractive x-ray lens

Abstract

Compound refractive x-ray lens is a unique device to form image of opaque object which is illuminated by x-rays. It is consisted of a lot number of placed in-line concave microlenses and works like ordinary refractive lens for visual light. In contrast to other x-ray optical devices, it could achieve satisfying resolution without complicated equipment. The spherical compound refractive x-ray lens used in this experiment is composed of 123 biconcave microlenses of 200 μm diameter. Each microlens was formed by the epoxy between two bubbles which were injected into an epoxy-filled glass capillary. There are three advantages ensuring good image quality of the lens for using in hard x-rays: (1) The epoxy (C100H200O20N, 1.08 g/cc) is composed of carbon, hydrogen and nitrogen, each of them is characterized by a low absorption coefficient for 5-30 keV x-rays. (2) Because of the nature of physics forming the bubble, the lens surface quality is extremely good. (3) The capillary makes sure that the series of unit lenses are well aligned coaxially. The lens focal length is 114 mm at 8.05 keV which is adjusted according to thick-lens analysis. X-ray images of grid mesh are compared between using a copper anode x-ray tube without filter and a synchrotron radiation source with monochromator. It could be found that the resolution and contrast are improved a lot by using monochromatic x-rays. The field of view and geometrical distortion around the edges of the field of view are reduced because of using a synchrotron radiation source. For x-ray tube as source the lens achieved a spatial resolution of 5 μm and field of view of about 700 μm. For a synchrotron radiation source, that is 3.8 μm by 2.3 μm resolution and field of view of about 316 μm by 128 μm.