Automated 3D Particle Field Extraction and Tracking System Using Digital in-line Holography

Digital holography for 3D particle field extraction and tracking is an active research topic. It has a great application in realizing characterization of micro-scale structures in microelectromechanical systems (MEMS) with high resolution and accuracy. In-line configuration is studied in this study as the fundamental structure of a digital holography system. Digital holographic approach, not only eliminates wet chemical processing and mechanical scanning, but also enables the use of complex amplitude information inaccessible by optical reconstruction, thereby allowing flexible reconstruction algorithms to achieve optimization of specific information. However, owing to the inherently low pixel resolution of solid-state imaging sensors, digital holography gives poor depth resolution for images. This problem severely impairs the usefulness of digital holography especially in densely populated particle fields. This study describes a system that significantly improves particle axial-location accuracy by exploring the reconstructed complex amplitude information, compared with other numerical reconstruction schemes that are merely traditional optical reconstruction. Theoretical analysis and experimental results demonstrate that in-line configuration presents advantageous in enhancing the system performance. Greater flexibility of the system, higher lateral resolution and lower speckle noise can be achieved.