In-Line Quality Control of Micro Parts using Digital Holography

We demonstrate a digital holographic system for the fast inspection of the interior of micro parts, which is capable of working in an industrial environment. We investigate micro objects using Two-Wavelength-Contouring with a synthetic wavelength of approximately 90 mu m. Special consideration is given to the mechanical robustness of the system. A compact Michelson-setup in front of the imaging optics increases the robustness for the measurement as the light paths of the object and reference have almost a common path. We also implement the Two-Frame Phase Shifting method for the recording of a complex wavefield. The use of two cameras for different polarized states for the object-and reference wave allows the recording of a complex wavefield in a single exposure per wavelength. The setup allows determining the shape of the interior surface of the object and faults such as scratches with a measurement uncertainty of approximately 5 mu m.