Tomographic diffractive microscopy with isotropic resolution

Microscopy techniques allowing observation of unlabeled samples have recently experienced a regain of interest. In particular, approaches based on recording of the optical field diffracted by the specimen, in amplitude and phase, have proven their capacities for biological investigations. When combined with variations of specimen illumination, tomographic acquisitions are possible. One limitation of previously developed approaches is the anisotropic resolution, characteristic of all transmission microscopes. In this context, an instrument, characterized by isotropic high-resolution 3D imaging capabilities, is still awaited. For the first time, to the best of our knowledge, we have developed tomographic diffractive microscopy combining specimen rotation and illumination rotation, which delivers images with (almost) isotropic resolution below 200 nm. The method is illustrated by observations of nanoscopic fiber tips, microcrystals and pollens, and should be helpful for characterizing freestanding natural (diatoms, spores, red or white blood cells, etc.) or artificial samples.