We have developed a tomographic diffractive microscope, equipped with a fluorescence confocal scanner. We measure experimentally the lateral resolution using an edge method and by comparing tomographic images of the same samples with wide-field and laser scanning confocal microscopy images; a scanning electron microscope image serves as a reference. The experimental resolution is shown to be to about 130 nm, or lambda/(3.5 NA). This instrument also permits one to measure 3D, complex index of refraction distributions, a quantity that is not accessible to conventional microscopes, and we show how this feature may be used to observe KCl crystals, absorption of which is very weak.

Abstract. We present an optical tomographic diffractive microscope, a device able to image a complex refractive index distribution in three dimensions. Theoretical foundations are first recalled: diffraction under the first Born approximation explains the link between diffracted beam, object frequencies and physical properties of the object. We then describe our experimental setup, recording 2-D interferograms in the image space, and detail the image reconstruction process underlying our tomographic microscope, which involves 2-D transforms of the recorded interferograms, a peculiar 3-D mapping of the data, and a final 3-D Fourier reconstruction. We apply tomographic reconstruction to diatom skeletons, unicellular algae with cell walls made of silica, and compare it to holographic reconstruction. We further apply it to pollen grains and show differences between the real and imaginary parts of the measured complex refractive index. Finally, we also recall alternative tomographic methods.

We report a tomographic diffractive microscope, which permits imaging non-labelled transparent or semi-transparent samples. Based on a combination of microholography with a tomographic illumination, our setup creates 3-D images of the index of refraction distribution within the sample. One acquires successively interferograms, rotating the illumination (the specimen being static) and using phase-shifting holography. Within the first Born approximation, each interferogram is interpreted as a subset of the Fourier transform of the specimen index of refraction distribution. The reconstruction is therefore similar to synthetic aperture imaging: one recombines the information in the Fourier space, and a final Fourier transform gives a 3-D image of the specimen. First recalling the theoretical foundations, we then describe our experiment, and show initial results obtained on biological samples.

International audienceWe have developped a tomographic diffractive microscope in reflection, using a high numerical aperture objec- tive and equipped with a fluorescence confocal scanner. We describe the set-up and first images of a microscopic USAF target, obtained in holographic, diffractive tomographic, and confocal mode, and which reveal the higher resolution capabilities of this instrument. We also compare images obtained in transmission and in reflection, emphasizing the better optical sectionning capabilities of reflection diffractive tomographic microscopy

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