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23 February 2006 Multi-wavelength phase imaging interference microscopy
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Multi-wavelength phase imaging interferography is a technique that combines phase-shifting interferometry with multi-wavelength phase unwrapping. It can be used to obtain phase profile of an object without 2π ambiguities inherent to single wavelength phase images. In this technique, a Michelson-type interferometer is illuminated by an LED and the reference mirror is dithered for obtaining interference images at four phase quadratures, which are combined to calculate the phase of the object surface. The 2π discontinuities are removed by repeating the experiment using two or three LEDs at different wavelengths, which yields phase images of effective wavelength much longer than the original. The resulting image is a profile of the object surface with a height range of several microns and noise levels of 10's of nm. The technique is applied to imaging of phase profile of microscopic objects. The interferographic images using broadband source are significantly less affected by coherent noise, and there are a number of other advantages, such as lower cost and ease of operation.
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Nilanthi Warnasooriya and Myung K. Kim "Multi-wavelength phase imaging interference microscopy", Proc. SPIE 6090, Three-Dimensional and Multidimensional Microscopy: Image Acquisition and Processing XIII, 60900U (23 February 2006);

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