Refractive index tomography with structured illumination

To probe biological questions with significant biophysical, biochemical, and molecular components, an imaging solution compatible with both endogenous and molecular 3D imaging may be necessary. In this work, we show that structured illumination (SI) microscopy, popularly associated with 3D fluorescent super-resolution, can allow 3D refractive index (RI) reconstructions when operated in the coherent realm. We introduce a novel reinterpretation of coherent SI, which mathematically equates it to a superposition of angled illuminations. Raw acquisitions for standard SI-enhanced quantitative-phase images can be processed into electric field maps of the sample under angled illuminations. Standard diffraction tomography (DT) computation can then be used to reconstruct the sample's 3D RI distribution at sub-diffraction resolutions. We demonstrate this concept by using SI to computationally reconstruct 3D RI distributions of human breast (MCF-7) and colorectal (HT-29) adenocarcinoma cells. Our experimental setup generates SI patterns using broadband illumination with a spatial light modulator and detects angledependent sample diffraction through a common-path, off-axis interferometer with no moving components. This technique may easily pair with SI fluorescence microscopy and important future extensions may include multimodal, sub-diffraction resolution, 3D RI, and fluorescent visualizations. (C) 2017 Optical Society of America