Laser Metrology and Machine Performance XIII The Performance of a Lensless Fibre- Deployed Low Coherence Interferometer for In-Situ Measurements T. Hovell, R. S. Matharu, L. Justham, J. Petzing, P. Kinnell Loughborough University, United Kingdom Abstract The need for increased geometric complexity and accuracy in manufactured parts is being industrially driven by sectors such as automotive, aerospace, medical, and energy generation. It is important to not only have traceable measurement systems in place for component geometry and tolerance conformance verification, but also to aid in the control of the material removal process in real-time on machine. Low Coherence Interferometry (LCI) has been developed and primarily used in the biomedical imaging domain for the past 20 years as Optical Coherence Tomography (OCT). During this period, it has been shown to be a powerful imaging modality with the ability to operate down to micrometre resolution for depth measurements in non-ideal environments. However, literature defining the effectiveness of lensless LCI/OCT systems operating outside of the biomedical domain is more sparse. Furthermore, the impact of system component choice on key output parameters has not been considered. In this work, the characterisation of a lensless, fibre deployed LCI system in a common path configuration is performed whilst varying system components. Geometric measurements are demonstrated both in air and in water, with analysis of the impact of system design and componentry on output performance metrics. Relative and absolute traceability of results are produced from calibration grade gauge blocks and Renishaw XL-80 calibration experiments to determine and underpin metrological statements of operating characteristics of the system. 1 Introduction Industrial demands for one-off customised production of components in sectors such as automotive, aerospace, medical and energy generation has led to the requirement for improved manufacturing process control, so processes are able to adapt to provide the required product geometry and surface roughness [1]. This type of process control is only possible through the incorporation of a traceable measurement device during the manufacturing process to provide real-time process feedback for tool inputs. Therefore, new compact and robust sensors that can be easily integrated within the process are required. Fibre-based sensors are of particular interest as they are extremely compact in nature and are inherently robust to many harsh operating conditions. Low coherence interferometry (LCI) has been shown to be a useful tool for absolute ranging and tomographic measurements in optical fibre defect detection and biomedical applications [2, 3]. LCI has also been able to provide