Characterisation of the internal structure and local optical properties of thick layers of hydroxyapatite by Coherence Probe Microscopy

Thick transparent or semi-translucent layers are of growing importance in several key scientific and technological fields such as microelectronics, nanotechnology and biomaterials. New characterisation tools are required to cope with the complexity of these new materials and with the large range of scales involved (nm, μm, mm). In this paper, we report work on the development of new optical imaging instrumentation for characterising such layers, based on scanning white light interferometry. We demonstrate that as well as being able to measure surface roughness and shape, scanning interferometry can also be used to measure the local effective refractive index, reflectivity spectra and internal structure, using point Z-scanning and 2D cross sectional profiling. Results are shown for thin diamond-like carbon layers on polycarbonate and thick layers of hydroxyapatite.