Advancements in Soft X-ray Diffraction Gratings for the Hefei Advanced Light Facility

Abstract

The Hefei Advanced Light Facility (HALF) is a fourth-generation diffraction-limited soft X-ray synchrotron radiation facility currently under construction in China. As key dispersion components, soft X-ray diffraction gratings are indispensable to the monochromators and spectrographs of HALF. To meet the urgent demand for high-performance soft X-ray diffraction gratings for HALF, our research group has developed fabrication technologies for equidistant gratings and varied-line-spacing (VLS) gratings featuring rectangular and triangular (blazed) groove profiles. This work builds on our more than four decades of research experience in holographic lithography combined with ion beam etching. This paper outlines recent advances in the fabrication of diffraction gratings for the HALF project and presents representative experimental results of the fabricated gratings. At present, the maximum length of the fabricated gratings reaches 200–300 mm. The central groove density of both equidistant gratings and VLS gratings ranges from 100 to 3000 lines/mm. The groove density precision of VLS gratings can reach the order of 10–6, with a spectral resolving power of more than 50,000. In addition, the blazed angle of the gratings can be controlled within 1°, which is applicable to blazed gratings with a groove density of several hundred lines/mm. The demonstrated high-precision control techniques for the spatial distribution of grating line density and blaze angle not only pave the way for fabricating high-end diffraction gratings, enabling high-resolution, high-throughput spectrometers at HALF, but can also be extended to provide critical technical support for constructing other cutting-edge scientific facilities such as synchrotron radiation sources and free-electron lasers.