Theoretical And Experimental Studies On Common-path Interference Microscopy

Interference microscopy, which combines optical interferometry and microscopy,is a whole-field optical technique for measuring profile, thickness or refractive indexdistribution of microscopic specimen. It has the advantages of nondestructive,high-resolution, high measurement speed, requiring no extra preparation on specimen.Thus, it has been widely used in biology, medical science, micro-fabrication industry,and so on. In this thesis, high-performance interference microscopy based oncommon-path configuration and parallel phase-shifting mechanism, as well as thecorresponding phase reconstruction algorithm are investigated. For these purposes, thefollowing works have been completed:1. A new common-path and in-line point-diffraction interferometer for quantitativephase microscopy is proposed. The magnified tested wave is split by a diffractiongrating into two copies. One copy is recast for reference wave through pin-holefiltered in the Fourier plane; the other one is still used as object wave. Afterdiffracted by the second grating, the two waves propagate on-axis into the CCDcamera. Achromatic phase-shifting is implemented by linearly moving one of thetwo gratings in grating vector direction. The setup has advantages of lesssensitive to environmental vibration due to the common-path configuration.2. Zernike phase contrast microscopy is extended to perform quantitative phasemeasurement for microscopic object by combining with the phase-shiftingtechnique. The extended microscopy uses dozens of periodic point-like lightsources on a ring for illumination, and corresponding point-like phase-shifters forphase retardering the undiffracted component of object wave. By shifting thephase shifters with different height (to cover the undiffracted components), thephase shifting can be performed. The method has low coherent noise level due tothe partially-coherent illumination. Besides, it has higher lateral resolutionbecause of the Synthetic-Aperture of the oblique illumination.3. The methods for simultaneous phase-shifting interferometry, which is based onparallel-beam-splitting and polarization phase-shifting, have been investigated. A diffraction grating pair or cube beam splitters are employed to perform theparallel-beam-splitting. Combined with polarization phase-shifting technique, theparallel phase-shifting unit is constructed. The unit has been incorporated intointerference microscopy. Two or more phase-shifting interferograms are obtainedthrough single exposure, thus moving object or dynamic process can be measuredwith this technique..4. A common-path and parallel phase-shifting point-diffraction interferencemicroscopy is proposed based on a cube beamsplitter pair. Together with theparallel phase-shifting scheme, slightly-off-axis interferometry for microscopy isperformed, which suppresses dc term by subtracting the two phase-shiftingholograms from each other. The setup is stable due to its common-pathconfiguration, and can be used for measuring moving object or dynamic process.5. A novel algorithm of phase reconstruction based on integral of phase gradient ispresent. The algorithm directly derives two real-valued partial derivatives fromthree phase-shifted interferograms. Through integrating the phase derivatives, thedesired phase is reconstructed. This algorithm is fast and easy to implement, andinsensitive to the nonuniformity of the intensity distribution of the interferogram.6. A simple algorithm for blind extraction of phase-shifts is proposed for from onlythree interferograms. Based on the statistical property of object wave, thealgorithm calculates approximately the involved phase-shifts as initial values.Then, the extraction is further improved by an iterative method, considering thefact that the closer the phase-shifts approach to their real values, the moreuniform the reconstructed reference wave will become. This method has theadvantages of fast extraction, no extra measurement, and high-precision.