Quasi-Isotropic High-Resolution Fourier Ptychographic Diffraction Tomography with Opposite Illuminations

Optical diffraction tomography (ODT) is a powerful toolfor thestudy of unlabeled biological cells thanks to its unique capabilityof measuring the three-dimensional (3D) refractive index (RI) distributionof samples quantitatively and noninvasively. In conventional transmissionODT, however, certain spatial frequency components along the opticalaxis cannot be measured due to the limited angular coverage of theincident beam, resulting in a poor axial resolution several timesworse than the lateral one. In this Letter we propose a new type ofODT method, termed opposite illumination Fourier ptychographic diffractiontomography (OI-FPDT), which produces almost isotropic resolution bycombining transmissive angle-scanning and reflective wavelength-scanning.Without resorting to interferometric detection, OI-FPDT requires anintensity-only measurement, and the forward and backward scatteredintensity images are synthesized in the Fourier space to recover the3D RI distribution of samples based on an iterative ptychographicreconstruction algorithm. To the best of our knowledge, this is thefirst time that near-isotropic resolution (similar to 274 nm) of ODTresult is obtained in a non-interferometric and sample motion-freemanner. Results of simulated cell phantom, tailor-made fiberglass,and onion epidermal cell samples confirm the validity of the proposedmethod.