<title>Holographic common-path interferometer for measuring tilt or vibrations utilizing a spatial heterodyne principle</title>

Abstract

A novel technique for extending the unambiguous range for differential measurements of linear surface deflections is presented. The principle utilises a new type of spatial heterodyne system, where a common-path interferometer probes the axial displacement of three points on the object surface simultaneously. The system is based on a single laser diode with all the optical functions of the system implemented in a single holographic optical element (HOE). The common-path scheme combined with the HOE provides a system that is inherently stable, since the HOE operates both as transmitter and receiver in the system. The HOE at the same time provides a simple and all passive quadrature phase measurement without the need for any active elements or polarising optics. The system is compact, robust, and has the potential for being mass-produced at a low cost and is thus well suited for industrial use. The demonstrated system can measure vibrations or tilt with an unambiguous dynamic range of approximately 1:14,000. Furthermore, the system can easily be reconfigured for a desired sensitivity and dynamic range.