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Multi-beam Spatially Multiplexed Interferometric Microscopy (MB-SMIM) is presented as the implementation of a robust, fast and accurate single-shot phase-estimation algorithm with a simple, low-cost and stable way to convert a bright-field microscope into a holographic one using partially-coherent illumination. Ronchi diffraction grating is used to generate two-beam and multi-beam interference. To ensure effectiveness of the process object field should be divided into analyzed specimen area (1/3) and clear reference area (other 2/3). Using partially coherent light source one is able to produce pure three-beam interference of -1 diffraction order of specimen area, and 0/+1 diffraction orders of both clear reference areas. Opposite sign orders create doubled spatial frequency term overlapping with the regular SMIM interferogram. Phase demodulation based on the single-frame two-dimensional Hilbert-Huang transform or regular multi-frame phase-shifting follows. Single-frame processing is more beneficial for increased spatial frequency term when doubled number of fringes “samples” the same phase variation as in regular SMIM interferogram. Adding (or subtracting) two three-beam interferograms phase shifted by π allows one to accurately isolate doubled (or single) spatial frequency fringe pattern. Altogether, MB-SMIM adds quantitative phase imaging capability to a commercially available non-holographic microscope with improved phase reconstruction: noise reduction, spatial frequency doubling and phase change disambiguation capabilities. Proposed method enables common-path optical generation of doubled spatial frequency fringes only by slight object field manipulation – no mechanical doubling of incident angle is needed. The technique has been validated using a 20X/0.46NA objective in Olympus BX-60 upright microscope for prostate cancer cells phase imaging.
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