Design and fabrication of cascaded X-ray planar parabolic compound refractive lens

Abstract

Due to its attractive features such as compact size, simple to align and wide working range of photon energy, the X-ray compound refractive lens (CRL) has gradually become one of the standard accessories to focus the X-ray beams from the synchrotron radiation light source. In this paper, a cascaded planar parabolic CRL is designed and fabricated. The novel CRL is composed of type Ⅰ and type Ⅱ refractive elements in order to achieve a small spot size while maintaining the transmission. In type I refractive element, the parabolic geometry aperture (R0) is large, while, in type Ⅱ refractive element, the radius of curvature (R) at the parabolic vertex is small. So N1 numbers of type I and N2 numbers of type Ⅱ refractive elements are cascaded to form a single-chip CRL. A cascaded X-ray planar parabolic CRL is constructed using PMMA material by means of LIGA techniques. The main structural parameters of type Ⅰ refractive elements are: N1=15, R1=200 μm, 2R01=564 μm. The main structural parameters of type Ⅱ refractive elements are: N2=20, R2=50 μm, 2R02=140 μm. The cascaded planar parabolic CRL is tested on the beam line whose original incident X-ray spot is 200 μm×100 μm at Shanghai synchrotron radiation facility. The measured lateral focusing spot size is 24.9 μm@8 keV, the transmission rate is 2.19% and the focal length is 1.052 m.