Digital Holographic Micro-Interferometery for the Measurement of the Refractive Index of Biological Cells
A digital holographic microscope that can be used to measure the refractive index of biological cells at different wavelengths that extend to the near-infrared spectrum was built. The interference pattern produced by the reference and object beams was recorded by a CCD camera. The recording process followed a special procedure called decoupling procedure . Three digital holograms with different interference patterns were recorded by varying the refractive index of the cell medium. In order to measure the refractive index of the cell medium and its variation, in the wavelengths that include near-IR spectrum, an Abbe Refractometer, which was modified by complementing it with CCD camera, is used. Moreover, in order to extract the interference phase from the recorded holograms, a program that applies Fourier fringe analysis to extract wrapped phase image and quality-guided phase unwrapping program were implemented in LabVIEW®. From the three different interference phase distributions of these holograms and the refractive index and its variation of the cell medium, four linearly independent phase difference equations, between the reference and object beams, were formulated. The four equations were then used to solve the refractive index and height of the cell that appear coupled in the phase difference equations.
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