Multilayer Mirrors Used For Space EUV Imagers

Space weather has great impacts to the earth’s space environment, human survival, production, scientific research and national security. Space wheather is the result of interactions of the solar activities, the earth magnetic field, and the location of the earth in the solar system, while the solar activities are the main driving source. EUV space imager is one of the most important instruments to observe the solar activities and the earth’s plasmasphere. EUV multilayer mirror is the key component of the imager, and the mirror’s optical characteristics determine the main performance of the imager.The material pairs, such as Mo/Si、B₄C/Si、B₄C/Mg、SiC/Mg, and so on, are studied in this paper. The parameters of the multilayer structure were optimized, and the reflectivities of the multilayers were calculated by computer. In order to improve the reflectivity of multilayer mirror at 30.4nm, B₄C/Mo/Si was chosen, and the structure was optimized, and the reflectivity was calculated. The B₄C/Si+Mo/Si multilayer was chosen in the paper to improve the reflectivity at 17.1nm and 30.4nm channel in one mirror. The parameters of coating process were optimized by experiments and the Mo/Si multilayers were fabricated by a magnetron sputtering coating machine. The reflctivities of the multilayer mirrors at 13.0nm, 17.1nm, 19.5nm and 30.4nm were measured by a laser-plasma reflectometer.The stability of the optical characteristics of the Mo/Si multilayers in high tempertature and intense radiation environment were discussed here. Experimental results shows that the Mo/Si multilayer has excellent thermal stability below 200℃. The concentration distributions of the protons and defects in the multilayer after radiation of protons with energy of 10keV and 60keV were analogized by the Monte Carlo method. The optical characteristics of Mo/Si multilayers were investigated before and after radiation, and the experimental results showed that the more doses the more damage in the multilayer. The variation of the reflectivity of the Mo/Si multilayer at 30.4nm were measured in the paper, and the results showed that the reflectivity reduced 2.8% at the initial 5 months after fabrication, and then became basically stable later.