Optimization analysis of partially coherent illumination for refractive index tomographic microscopy

Partially coherent optical diffraction tomography (PC-ODT) is a well-established label-free quantitative threedimensional (3D) imaging technique based on the refractive index (RI) contrast by measuring the intensities at multiple axially displaced planes. The imaging performance of tomographic RI microscopy is determined by the inversion of phase optical transfer function (POTF) which depends on the illumination pattern of imaging system. Here, we propose the optimization analysis of illumination pattern in PC-ODT, and the custom-build quantitative criterion is demonstrated to maximize the performance of POTF related to the "goodness" evaluation of an illumination aperture. Source modulation with different segment scale and gray scale is implemented to acquire arbitrary distribution source, and the corresponding 3D POTF can be easy obtained through the numerical incoherent superposition of each segment components. Moreover, the metrics of 3D POTF for various illuminations over the condenser aperture are analyzed. We test the obtained optimal illumination by imaging both a simulated micro phase bead and a real control bead sample, suggesting superior performance over other suboptimal patterns in terms of both SNR and spatial resolution. Further, experimental result based on unstained MCF-7 cell clusters is presented support this finding as well, and the proposed method is expected to find versatile applications in biological and biomedical research.