Coherence Control and Wavelength Correction in Multi-Wavelength Digital Holography

Accurate surface measurement and alignment are increasingly vital in industrial manufacturing, where both extended axial range and sub-micrometer precision are essential. Multi-wavelength Digital Holography (MDH) achieves this by generating synthetic phase maps through digital combination of multiple laser wavelengths. This work presents two key innovations that enhance the robustness and practicality of MDH for industrial surface metrology. First, we introduce a coherence control technique using a dynamic mode-mixing process with a phase-randomizing mirror and bent multimode fiber to suppress coherent noise by tailoring the illumination coherence length. Second, we develop a post-processing algorithm that detects and compensates for wavelength shifts using an order parameter derived from residual phase maps, enabling accurate phase unwrapping even with unstable or low-cost laser sources. Together, these contributions enable MDH to deliver reliable, phase-jump-free heightmaps with sub-micrometer accuracy over mesoscopic ranges in realistic manufacturing environments.