[Development of soft X-ray multilayer mirror at 23.4 nm]

To meet the research requirement of Ne-like Ge X-ray laser, we designed and fabricated soft X-ray multilayer mirrors at 23.4 nm. New material combination Ti/Si has been chosen based on the material selecting rule, considering the optical characteristics and physicochemical characteristics. Then the period thickness (d), material ratio (gamma), and period number (N) of the multilayer were optimized and the reflectivity was calculated by software. The coating parameters were optimized through experiments and the Ti/Si multilayer mirrors at 23.4 nm were fabricated by magnetron sputtering coating machine. The mirrors were tested by X-ray diffractometer and soft X-ray reflectometer after fabrication. The test results of the Ti/Si multilayer were lambda0 = 23.2 nm and R = 25.8%. Compared with Mo/Si multiplayer, which is generally used in soft X-ray region, the reflectivity of Ti/Si multilayer increases 10% approximately, and FWHM narrows by 1.8 nm at 23.4 nm, indicating better optical performance.