A Dispersed Reference Interferometer for Surface and Dimensional Metrology

Successful integration of miniaturised metrology instruments with manufacturing processes will enable reduction in costs for the manufacture of high and ultra-precision components and assemblies. We present a novel interferometric method of absolute single point position measurement. Through use of a short coherence near-infrared light source and introduction of chromatic dispersion in the reference arm, a measurement system with high dynamic range is achieved without the requirement of slow mechanical scanning or expensive chromatically abberated probes. Small remote probes connected to the interrogation apparatus by fibre allow for reduction in environmental noise and measurement of traditionally difficult to measure locations. Use of a common reference and measurement path to and from the probe further reduce environmental noise suffered by the fibre. The interrogation apparatus is arranged in a Michelson interferometer configuration and consists of a superluminescent diode (SLD), a beam splitter, an objective lens, a matched pair of blazed transmission gratings and a spectrometer; the layout of this is described. Also presented are the principles of operation along with initial results which including measurements of range, vertical resolution, linearity and stability. Lastly, use of the described interferometer with multiple fibre linked probes is discussed.