Optical Phase Contrast Microscopy with Incoherent Vortex Phase

Abstract A novel, compact, and broadband optical phase contrast microscopy based on incoherent vortex topological quadrupole is theoretically proposed and experimentally realized. The topological quadrupole, generated in a thin uniaxial crystal, possesses four single‐charge optical vortexes, each of which can act as a two‐dimensional (2D) optical spatial differentiator. The incoherence of light‐emitting diode (LED) light will wash out the optical vortex and the spatial differentiation effect, which can be ingeniously overcome by choosing Kohler illumination and inserting a 1 mm‐thickness uniaxial crystal sandwiched with two polarizers before the camera. By adjusting the polarizers and the tilted angle of crystal to selectively utilize the geometric Berry phase and the angular gradient of Fresnel transmission coefficients of crystal, the 1D, 2D, and second‐order analog spatial differentiations with a spatial resolution better than 0.775 μm can be switched flexibly. A versatile phase contrast microscope is built, which is well compatible with the conventional microscopes. The uniformly incoherent illumination without laser speckle effects results in high‐quality spatial differentiation imaging. Biologically transparent living cells are thus imaged with high contrast.