Zone-plate Interferometers

Abstract

Interferometry gives a precise indication of the relative separation of two coherent sources. If the sources are images produced by an optical system, their positions are controlled by the respective components of the system. Interferometry can therefore be used to measure the relative positions, in three-dimensions, of the optical components. This paper describes a common-path interferometer which uses zone plates as beam-splitting and imaging components. A two-dimensional array of reflective zone plates is used to define a three-dimensional array of positions, i.e. an optical ‘space frame’. Particular examples of wavefront geometry are used to show how the sensitivity to displacement can be varied by controlling the relative shear of the wavefronts. The device has applications in metrology, for example in checking the positioning performance of multi-axis measuring machines.