Towards absolute measurements using multiwavelength digital holography

Multiwavelength digital holography (MWDH) is a high-speed (< 1s) and high-precision (sub-micrometer) measurement technique that enables precise optical surface metrology. State-of-the-art MWDH systems, such as the HoloTop NX sensor (Fraunhofer IPM), can be used on coordinate measurement machines (CMMs) or even industrial robots. Apart from mechanical and environmental disturbances that cannot be avoided with these handling systems, combining multiple measurements without overlapp is nearly impossible. This is due to the relative nature of the captured phase information, limited up to the uncertainty of the synthetic wavelength. To address this issue, we propose an absolute-referenced MWDH concept anchoring data to the interferometer’s zero point (ZP), determined with an electro-optically driven synthetic wavelength generator. The latest experiments show consistent and repeatable ZP localization. Finally, we show a measurement of our sensor on a Stäubli TX2-90L industrial robot and discuss future applications using the proposed method.