Optical diffraction tomography with fully and partially coherent illumination in high numerical aperture label-free microscopy

Quantitative label-free imaging is an important tool for the study of living micro organisms which during the last decade has attracted wide attention from the optical community. Optical diffraction tomography (ODT) is probably the most relevant technique for quantitative label-free 3D imaging applied in widefield microscopy in the visible range. The ODT is usually performed using spatially coherent light illumination and specially designed holographic microscopes. Nevertheless, the ODT is also compatible with partially coherent illumination and can be realized in conventional wide-field microscopes by applying refocusing techniques as it has been recently demonstrated. Here we compare these two ODT modalities underlining their pros and cons and discussing the optical setups for their implementation. In particular, we pay special attention to a system which is compatible with conventional wide-field microscope and can be used for both ODT modalities. It consists of two easily attachable modules: the first one for sample illumination engineering based on digital light processing technology and another one for focus scanning by using an electrically-driven tunable lens. This hardware allows for a programmable selection of the wavelength and the illumination design, as well as it provides fast data acquisition. Its performance is experimentally demonstrated in the case of ODT with partially coherent illumination providing specklefree 3D quantitative imaging.