The feasibility of extended range monolithic X-ray interferometric calibrators

Abstract

X-ray interferometry is now established as a technique for calibrating micro-displacement transducers to sub-nanometre accuracy and with excellent traceability over small displacement ranges. For translations over several micrometres, larger versions of the same monolithic design could be constructed, but many inherent error sources that may be neglected for short ranges are likely to become significant. This paper explores these sources including: the maximum scan for a silicon flexure; parasitic twisting of the flexures; strain from the flexure that affects the lattice used in calibration or distorts the metrology path. It proposes the incorporation of active compensation for parasitic twisting and various methods for improving fringe contrast. Methods of obtaining relatively fast scans are also discussed. Experimental evidence indicates that monolithic devices can be used for micrometre translations, but this may be the limit of usefulness for the current designs. This leads to a discussion of alternative geometries including a proposal for a new high-performance monolithic calibrator.