Measuring the divergence of laser beams to correct interferometric displacement measurements

Owing to the impossibility of a plane-wave illumination, diffraction affects optical interferometry applied to the measuring of linear displacement. Therefore, the measurement of the beam divergence is essential to calculate the needed corrections. This paper examines a measurement method relying on the Fourier optics. Particular emphasis is given to the assessment of systematic errors in the measurement of the Si lattice parameter by combined X-ray and optical interferometry.