Proceedings Article | 29 February 2008
Proc. SPIE. 6859, Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues VI
KEYWORDS: CMOS sensors, Metals, Microscopy, Image sensors, Phase imaging, Optical vortices, Photomasks, Digital image correlation, Phase measurement, Spiral phase plates
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".
