Improving depth image acquisition using polarized light

Control of the source and analysis of the polarization properties of the reflected light in a laser rangefinder based on triangulation offer a potential solution to the problem of distinguishing the primary laser stripe from unwanted inter-reflections caused by holes and concavities on metal surfaces. In this paper, the established polarization theory of first and subsequent inter-reflections from metallic surfaces is reviewed. This provides a point of comparison for ellipsometric measurements which verify the particular applicability of the microfacet surface model in our context. We demonstrate how a conventional laser rangefinder can be modified to discriminate between primary and secondary reflections. However, our experiments on third and subsequent reflections show that more complex models are required to provide complete resolution of the problem. Furthermore, error analysis demonstrates the requirement for very precise control of the source and receiving optoelectronics. We conclude by demonstrating the acquisition of a depth image with and without polarization optics and discuss the significance of our results for laser depth measurement.