| The VUV and EUV spectral region below 110 nm has becoming a interesting research area due to applications of different fields,such as solar physics, atmosphere physics, space communication and space weather forecast. However, it is difficult to design the high reflectivity mirror in this spectral region.The reason is the reflectivity of single layer and standard multilayers can not meet the application demand due to the high radiation absorption of all materials in this spectral region. Consequently, it is important to find suitable method to enhance the reflentivity in this spetral region. In 2001,Larruquert provided a new design method of sub-quarter-wave multilayers which is effective to enhance the reflectivity at certain wavelength.By now, the research of broad band high reflectivity mirrors has not been made deeply. The paper attempt to design and fabricate broad band multilayers by the method of sub-quarter-wave multilayers.The design method of sub-quarter-wave multilayers with enhanced normal reflectance in the strong absorbing range 50-110 nm has been presented .The multilayers consisted in the superposition of a few layers of strong absorbing materials. The optical thickness of each layer in the multilayers is less than quarter-wave thickness. Compared to the standard multilayers, this multilayer structure more suits to enhance reflectance of strong absorbing wavelength range. The high reflectance multilayers Si/W/Co was designed at wavelength of 50 nm by using this method, and then optimized based on this initial condition by using Levenberg-Marquart algorithm in a wide wavelength range 50-110 nm. The calculated results suggest that the reflectance of the multilayer is as high as 45%. The sample was fabricated by using a high vacuum direct current magnetron sputtering. Then, the multilayer was characterized by a low angle X-ray diffraction. The results suggested that the fabricated multilayer structure meets the design requirement.
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