软X射线多层膜设计中表面粗糙度对反射率的影响

给出了一种改进的软X射线波段的多层膜设计方法.在设计过程中,考虑了反射镜基底和各膜层之间的均方(RMS)粗糙度对反射率的影响 ;在Stearns提出的散射理论的基础上给出了粗糙界面的数学模型.文中以波长为λ=1.03nm的软X射线为例进行设计,设计结果表明 :要使波长为λ=1.03nm的多层膜的反射率大于10%,反射镜基底的均方粗糙度不应超过0.6nm.实验中选择几块表面粗糙度为 0.5nm(RMS)的熔石英平面镜作为基底来制作适用于该波长的、层对数超过70的多层膜.然后在的入射角下测量反射率,测得的值为10%,这与采用本设计方法得到的计算结果一致.该反射镜作为X射线谱仪的分光元件被应用于惯性约束聚变(ICF)的过程诊断中.

Roughness effects on the reflectance in the design of a soft X-ray multi-layer mirror

In the design of a multi-layer mirror at λ=1.03 nm in soft X-ray regin, a modified method is presented, in which the effects of root-mean-square (rms) roughness of the substrate and interfaces between these films on the reflectance are considered and discussed. Then, the mathematical model for rough interfaces is given based on the scattering theory presented by D. G. Stearns. The design result shows that the substrate roughness (rms) should be smaller than 0.6 nm in order to fabricate a multi-layer mirror whose reflectance is greater than 10%. A few super-polished fused quartz substrates with 0.5 nm (rms) roughness are chosen in coating experiments. The measured reflectance is about 10% at λ=1.03 nm,which is consistent with the result acquired by the modified design method. The multi-layer mirror has been applied in a X-ray spectrograph for diagnosis of inertial confinement fusion (ICF).