Experiment on the absolute measurement of a silicon lattice spacing at the NRLM

An experimental setup for the determination of the silicon lattice constant is described. The monolithic flexure hinge mechanisms for orientation adjustment, an optical interferometer for angle and displacement measurement, and a special tool for establishing the parallelism between the optical surface and the reciprocal lattice vector are introduced. The latest experiment gives a value for the ratio of the optical wavelength to the silicon lattice spacing which is consistent with more established values within a currently large uncertainty of one.>