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2 May 2008 Biological samples observed with diffractive tomographic microscopy
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Many biological researches require observation of the sample at a sub-micrometer scale. However, most biological samples are transparent, and thus are barely visible in conventional transmission microscopy. Techniques like interference contrast or oblique illumination permit to record an improved contrast, but are useful for morphological studies only, because the interaction of incoherent, non-polarized and polychromatic illumination with matter is very complex, so that the recorded contrast cannot be linked to local physical properties of the sample, as for example the index of refraction. We have developed a diffractive tomographic microscope, which permits the observation of unstained-, transparent samples in 3-D. This device is based on a combination of microholography, which records the field diffracted by the specimen in both amplitude and phase using a high numerical aperture objective and a phase stepping interferometer, with a variable illumination of the sample (tomography) using a high numerical aperture condenser. The successive holograms are numerically recombined in the Fourier space, and the reconstruction of the specimen index of refraction distribution is based on the first Born approximation for weakly diffractive samples. Examples of biological specimens observed with this technique are given, and possible evolutions of the instrument are discussed.
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B. Simon, M. Debailleul, V. Georges, O. Haeberlé, and V. Lauer "Biological samples observed with diffractive tomographic microscopy", Proc. SPIE 6991, Biophotonics: Photonic Solutions for Better Health Care, 699112 (2 May 2008);

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