Two-dimensional differential interference contrast microscopy based on four-hole variation of Young's interference

We demonstrate a novel method of two-dimensional differential interference contrast (DIC) microscopy. Our method is cheaper, more compact, and more robust compared to conventional DIC microscopes; since it uses a simple variation of Young's double-slit geometry, no expensive or complex optical components are needed. In addition, our method quantitatively measures differential phase, unlike conventional DIC, which makes our device useful for optical metrology and cell biology applications. The device consists of four circular holes arranged in a "plus" pattern, milled into a metal layer 80 μm above a complimentary metal-oxide semiconductor (CMOS) image sensor. Light incident upon the four-hole aperture is transmitted through the holes and creates an interference pattern on the CMOS sensor. This pattern shifts as a function of the spatial phase gradient of the incident light. By capturing the amplitude and location of the zero-order fringe of the interference pattern, the amplitude and differential phase of the incident light can be measured simultaneously. In this article, we model the response of the device using both geometric optics and Huygens principle. We then verify these models by experimentally measuring the responsivity of our device. A short analysis on the algorithm used to calculate the fringe location follows. We then show a beam profiling application by measuring the amplitude and spatial phase gradient of a Gaussian laser beam and an optical vortex. Finally, we show a DIC microscope application; we image a phase mask of the letters "CIT".