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Digital holographic microscope with automatic focus tracking by detecting sample displacement in real time.
Pietro Ferraro1, Giuseppe Coppola, Sergio De Nicola
1Istituto per la Microelettronica e Microsistemi del Consigilio Nazionale delle Ricerche, Via P. Castellino 111 80134 Naples, Italy. p.ferraro@cib.na.cnr.it
Optics Letters
|July 30, 2003
Summary
This study introduces a new focus tracking method for digital holography, enabling automatic calculation of reconstruction distances for clear images even with sample movement. This technique is useful for inspecting microelectromechanical systems under thermal stress.
Area of Science:
- Optical Metrology
- Holographic Imaging
- Microscopy
Background:
- Digital holography records 3D information of microscopic samples.
- Axial displacement during recording can degrade image quality.
- Accurate focus is crucial for quantitative analysis of microstructures.
Purpose of the Study:
- To develop an automated focus tracking method for digital holography.
- To enable high-quality image reconstruction despite axial sample displacement.
- To apply the method for inspecting microelectromechanical systems (MEMS).
Main Methods:
- A novel algorithm for automatic focus determination is proposed.
- Calculation of corrected reconstruction distances for each hologram.
- Generation of well-focused amplitude and phase-contrast images.
Main Results:
- The method successfully tracks focus during axial displacement.
- Automated calculation of accurate reconstruction distances was achieved.
- High-quality, focused holographic images were obtained for MEMS inspection.
Conclusions:
- The proposed focus tracking method enhances digital holographic microscopy.
- It allows for reliable imaging of dynamic micro-systems.
- The technique offers a quasi-real-time solution for micro-component analysis.