This book describes the methods used to detect material defects at the nanoscale. The authors present different theories, polarization states and interactions of light with matter, in particular optical techniques using polarized light. Combining experimental techniques of polarized light analysis with techniques based on theoretical or statistical models to study faults or buried interfaces of mechatronic systems, the authors define the range of validity of measurements of carbon nanotube properties. The combination of theory and pratical methods presented throughout this book provide the reader with an insight into the current understanding of physicochemical processes affecting the properties of materials at the nanoscale.