Holography is an optical technique in which the wave nature of light is used to produce three-dimensional images of an object of interest. In addition to the flat 2D representation of a photograph, the holograph also records the depth of field by recording the phase of an incoming wave field. The principles of holography can also be used to examine the optical properties of transparent media. The refractive index of a transparent material is defined to be the fraction by which light slows down as it propagates through the medium. A digital holographic microscope (DHM) has been constructed to measure the refractive index of living biological cells as this information has been shown to be an indicator of cell health and is also central to cellular biomechanics measurements made with optical force instruments. In order to find the index, the DHM records interferograms which quantitatively measures laser light's change in phase as it traverses the cells. These interferograms are then processed to reveal the cell's refractive index and height. The theory and design for the DHM will be presented along with a full discussion of the interferogram processing algorithms. The experimental procedure will be outlined in detail, and verification for the integrity of the index measurements will be discussed. Finally, a summary of refractive index measurements made of EMT6 cells at several wavelengths will be presented.
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