Fabrication and test of quasiperiodic x-ray reflection gratings for high-order diffraction suppression (Conference Presentation)

Abstract

X-ray diffraction gratings with periodic structures have been widely used in various x-ray instruments and systems, such as synchrotron radiation, x-ray interferometer, x-ray astronomy and plasma diagnostics in the field of laser fusion. However, conventional diffraction gratings suffer from so-called high order diffraction contamination. Here we present a large-area quasiperiodic x-ray reflection grating fabricated by high-speed electron beam direct writing technique. The grating consists of a large number of circular holes for the high order diffraction suppression. The 3rd and even order diffractions can be completely eliminated, and the 5th order diffraction is as low as 0.02% of the 1st order diffraction. Shipley SAL-601 with high-resolution, high sensitivity and good resistance is used for electron beam lithography, followed by dry silicon etching and Au thin film deposition using magnetron sputtering. Since the surface roughness and flatness of the x-ray reflection gratings have a great impact on the dispersion performance, we optimized the fabrication the inductively coupled plasma (ICP) silicon etching process, and tested the surface roughness and flatness of the x-ray reflection gratings by an atomic force microscope and a Zygo interferometer, respectively. The optical characterization of the fabricated quasiperiodic x-ray reflection gratings was performed at the spectral radiation standard and metrology beamline BL08B, national synchrotron radiation laboratory of China. The test results demonstrated the effectiveness of high order diffraction suppression. The capability of high order diffraction suppression and fabrication constraints and the limitation of the diffraction efficiency of the quasiperiodic x-ray reflection gratings are also discussed. The unique high order diffraction suppression properties of the quasiperiodic x-ray reflection gratings may provide a platform for x-ray spectroscopic instruments in laboratory sciences and synchrotron light sources.