Abstract

Planar parabolic refractive lenses are one important kind of compound refractive lenses which are used in the third generation synchrotron radiation sources as an x-ray focusing device. In order to test the influence of the number of the individual lens on the transmission and gain, a set of 30 micro-focusing planar parabolic lenses with different number (from 1 to 30) of the individual lens was designed, which had equal apertures of 250 &mu;m and equal focal length of 30 cm at 8.05 keV. The parameters of the lenses were optimized for performing focusing test at x-ray diffractometer (XRD). The optical simulation was completed by ray tracing by the commercial program of ZEMAX. The radius of curvature at the tip of the parabola ranged from 1.23 &mu;m to 37 &mu;m and the theoretical transmission from 43.3 % to 33.2 %. The theoretical width of focal line was about 3.4 &mu;m. Ultra violet lithography was used to fabricate the planar lenses from SU-8 photoresist which thickness was 224 &mu;m. Measured dimension of lenses is coincident with the theoretical one. Focusing properties of the lenses were studied both at XRD and at U7B beamline at the National Synchrotron Radiation Laboratory (NSRL) at the energy of 8.05 keV. The detector was a Peltier-cooled, 1380 x 1030 format (6.45 x 6.45 &mu;m<sup>2</sup> pixels) charge coupled device with a fiber-optic-coupled scintillator (Photonic Sciences Ltd., "X-ray Fast Digital Imager"). The width of focal line was about 27.4 &mu;m with a gain of 7.17 for N=8 lenses which was achieved in the NSRL. The reasons for the big difference between theoretical values and measured ones were discussed.

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