30．4nm正入射成像系统滤光片

30.4 nm filter in normal incidence imager

多层膜反射镜是30．4nm正入射望远镜的主要反射元件，但它在紫外、可见和近红外光波段也具有很高的反射率，需要滤光片来消除这些长波辐射，而滤光片材料和膜层厚度对滤光片的性能起重要作用。根据原子散射因子，理论计算出几种材料波长和线性吸收系数之间的关系，确认铝足30．4nm波段滤光片的最好材料。在考虑透过率和膜强度的基础上，确定了滤光片的膜层厚度。改进了现有的由Mcpherson247掠入射软X射线-真空紫外单色仪和气体空心阴极光源组成的光谱测量装置，使其适合于透过率的测昔，其波长扫描精度为±0．017～±0．097nm，对所制备的铝滤光片进行25．6～1000nm波段的透过率测量，测量结果显示其在30．4nm处的透过率为58．85％。为了比较全面地反映该种滤光片的透过率情况，又测量了它在紫外、可见和近红外波段的透过率，其值接近零，证明了该滤光片可满足30．4nm成像系统的需要。

The muhilayer mirrors are primary reflectors in a 30. 4 nm normal incidence telescope. Beacause of its very high reflectivity in ultraviolet, visible light and near infrared wave band, it is very necessary to use some special filters to remove these longer wave radiations. Moreover,material and thickness have great influence on the performance of filters. By computing the relationship between linear absorption coefficients and wavelengths for several kinds of materia factor,it can be proved that aluminum is the best material for 30.4 nm fi s based on atomic scattering ter. The filter＇s thickness is determined by considering the transmission and hardness. The spectrum measurement instrument made of Mcpherson model 247 grazing incidence monochromator and gas hollow cathode source is improved, which is fit for transmission measurement with the wavelength scanning error of ±0. 017-± 0. 097 nm. The transmission of prepared filter is measured from 25.6 nm to 1 000 nm,and the results show that it is 58.85% at 30.4 nm. The results also demonstrate that the filter can be used in a 30.4 nm imaging system, since it can prevent UV,visible and near infrared light effectively.