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 distoits 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 wrrent designs. This leads to a discussion of alternative geometries including a proposal for a new high-performance mondithic calibrator.
A 'free-standing' microdisplacement calibrator is described which utilizes a previously proposed but untested design of monolithic x-ray interferometer. The monolith is driven by a twist-compensating electromagnetic actuator and a specially designed 1 ppm current source and is held, along with its x-ray source and detectors, within a desk-top-mounted radiation enclosure. It is confirmed that highly traceable displacements resolved to a small fraction of a nanometre can be obtained over a continuous range of at least 10 µm under conditions typical of a routine metrology room. An overview of the system and its performance is given, but this paper concentrates particularly on the monolith design and on vibration suppression
A monolithic x-ray interferometer has been developed which provides a means of producing high-quality x-ray Moiré fringes with readily controlled pitch (spacing). It was designed as a calibrator of sub-microradian angular displacements and it has successfully demonstrated the feasibility of the approach. The quality of its output, when combined with the phase imaging capabilities of interferometry and the latest generation of fringe analysis algorithms, suggests additional, novel applications. This paper first reviews the principles and performance of the system as an angular calibrator and then discusses the potential of x-ray Moiré patterns in the form of an x-ray microscope and as a diagnostic tool for ultra-precision metrology. Demonstration results are given mostly in the form of images of fringe fields, since the point here is the production of original data suitable for processing by existing techniques.
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