We propose a new method for focus tracking during the recording of a sequence of digital holograms while the sample experiences axial displacement. Corrected reconstruction distances can be automatically calculated, and well-focused amplitude and phase-contrast images can be obtained for each digitized hologram. The method is demonstrated for inspection of microelectromechanical systems subjected to thermal load. The method can be applied as a quasi-real-time procedure.
© 2003 Optical Society of America
(090.1760) Holography : Computer holography
(100.2650) Image processing : Fringe analysis
(120.4630) Instrumentation, measurement, and metrology : Optical inspection
(180.3170) Microscopy : Interference microscopy
Pietro Ferraro, Giuseppe Coppola, Sergio De Nicola, Andrea Finizio, and Giovanni Pierattini, "Digital holographic microscope with automatic focus tracking by detecting sample displacement in real time," Opt. Lett. 28, 1257-1259 (2003)