High resolution PS-OCT for material analysis

Optical Coherence Tomography (OCT) is an emerging technology for high-resolution non-contact imaging of semitransparent structures, which has been developed for biomedical diagnostics, like glaucoma or melanoma detection. Beside the conventional OCT exist several instrumental extensions which provide e.g. ultrahigh resolution to image even subcellular structures or which give additional information by measuring the polarizing properties of the investigated biological tissue (i.e. with polarization-sensitive OCT or PS-OCT). On the other side, the material research sector outside the biomedical field is up to now nearly totally unaware of the potential which OCT and its modifications can provide, especially in the field of non destructive testing and evaluation (NDT and NDE). Within this project the advantages of ultrahigh resolution OCT imaging and the detection of polarizing properties with PS-OCT are combined and applied for the first time to problems posed in material research. One of the main issues will be to improve the spatial resolution of the measurement system in order to image material features, like embedded fibres, grains, pores, with size down to 5 m. Especially for light weight material compounds like glass-fibre reinforced epoxy compounds, used e.g. as airplane parts or blades for wind turbines, NDE plays an increasing role. Non-destructive material evaluation like cross- sectional imaging and detections of faults and cracks and their evolution inside these composites materials will be of high importance and help to improve part performance, reliability and hence increase safety. Other envisaged applications cover the spatially resolved mapping of internal strain fields as they appear e.g. in high precision injection moulded plastic parts or the detection of anisotropic micro-pores in piezoelectric cellular polymer foils which will be used in the future as large area sensors (e.g. flat keyboards) or speakers

Optical Coherence Tomography (OCT) is an emerging technology for high-resolution non-contact imaging of semitransparent structures, which has been developed for biomedical diagnostics, like glaucoma or melanoma detection. Beside the conventional OCT technique several instrumental extensions were developed which provide e.g. ultrahigh resolution to image even subcellular structures or which give additional information by measuring the polarizing properties of the investigated biological tissue (i.e. with polarisation-sensitive OCT or PS-OCT). On the other side, the material research sector outside the biomedical field was up to now rather unaware of the potential which OCT and its modifications can provide, especially in the field of non destructive testing and evaluation (NDT and NDE). Therefore, within this project the advantages of ultrahigh resolution OCT imaging and the detection of polarizing properties with PS-OCT were combined and applied for the first time to problems posed in material research: the main issues were to improve the spatial resolution of the measurement system in order to image material features, like embedded fibres, grains, pores, with sizes down to the micrometer range and to simultaneously map the stress state within the material under investigation. To prove the capabilities of the novel OCT concept, the resulting setup was applied to the characterisation of light weight material compounds like glass-fibre reinforced polymers, used e.g. as airplane parts or blades for wind turbines, structures where NDE plays an increasingly important role. Non-destructive material evaluation like cross-sectional imaging and detections of faults and cracks and their evolution inside these composites materials are of high importance and help to improve part performance, reliability and hence increase safety. Other applications covered the spatially resolved mapping of internal strain fields within high precision injection moulded plastic parts or within photo-resist moulds for the fabrication of miniature gearwheels as used in novel compact drives.