Low-coherence interferometry – an advanced technique for optical metrology in industry

Low-coherence interferometry (LCI) is an optical technique that may be used for industrial surface metrology with accuracy in the micron range. An instrument made with optical fibres is rugged enough to be used in industrial environments and the fibre-linked optical probe may be miniaturised for accessing tight locations. Among industrial applications developed at IMI, several cases for which LCI has been particularly useful, such as an elongational rheometer (RME), characterisation of wear damages on coating and laser-induced breakdown spectroscopy (LIBS), will be presented. The RME is an instrument in which a polymer sample is stretched in a controlled temperature furnace at up to 350°C. LCI has been used for monitoring the thickness of the samples. Wear damage is quantified by the volume loss after a wear test. It requires a high depth resolution (axis perpendicular to the surface) but a relatively coarse transverse resolution. The LIBS is a technique that has been used for analysing the chemical composition of materials as a function of depth. LCI has been integrated to a LIBS instrument for measuring accurately the crater depth between each laser shot.