Surface profilometry by a holographic confocal microscopy

abstract

English

Confocal imaging by a holographic confocal microscope is based on the real-time incoherent-holography technique. In addition to the image intensity, the image phase is inherently reconstructed from the holographic signal. We proved experimentally that the image phase can be converted into the height map of the specimen surface. In this way, we measure the surface profile with the precision of several nanometers. Phase ambiguities appear in the phase images of surfaces containing large height steps. Then, the measured height of the step must be added by the term mz, where z denotes the height that corresponds to the phase difference 2pi and m is an unknown integer. We proved experimentally that the number m can be determined by means of the depth discrimination of the image intensity, by the measurement of the axial distance between the intensity maxima corresponding to the lower and upper region of the surface. During this measurement, the axial shift of the specimen was determined from the phase shift of the on-line reconstructed phase image of the surface. The measurement of m needs axial resolution of the microscope better than z. We proved experimentally that the axial resolution of the holographic confocal microscope can be substantially improved using spectrally broadband illumination instead of monochromatic one, according to the theoretical prediction. In this way, we reduced FWHM of the axial intensity response for a plane to one half of its value for a monochromatic illumination.

holographic applications, confocal microscopy, profilometry

CHMELÍK, R., LOVICAR, L., HARNA, Z.

1. 1. 2002

Institute of Physics , Wroclaw University of Technology

Krzyzowa, Polsko

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