The measurement of the angle between an interferometer’s front mirror and the diffracting planes is a critical aspect of the measurement of Si lattice parameters by combined x-ray and optical interferometry. In addition to being measured offline by x-ray diffraction, it was checked online by moving the analyser crystal transversely and observing the phase shift of the interference fringe. We describe the measurement procedure and give the miscut angle of the ²⁸Si crystal, whose lattice parameter was an essential input datum for the determination of the Avogadro constant in the past and which is now used in the definition of the kilogram, based on counting atoms. These data will benefit others that might wish to repeat the measurement of the lattice parameters of this unique crystal.

干涉仪前反射镜和衍射平面之间角度的测量是通过结合 X 射线和光学干涉测量法测量 Si 晶格参数的一个关键方面。除了通过X射线衍射离线测量外，还通过横向移动分析仪晶体并观察干涉条纹的相移进行在线检查。我们描述了测量程序并给出了²⁸ Si 晶体的错切角，其晶格参数是过去确定阿伏伽德罗常数的基本输入数据，现在用于定义千克，基于原子计数. 这些数据将使其他可能希望重复测量这种独特晶体的晶格参数的人受益。