Pupil function engineering for enhanced nanoparticle visibility in wide-field interferometric microscopy

Wide-field interferometric microscopy techniques have demonstrated their utility in sensing minute changes in the optical path length as well as visualization of sub-diffraction-limited nanoparticles. In this work, we demonstrate enhanced signal levels for nanoparticle detection by pupil function engineering in wide-field common-path interferometric microscopy. We quantify the improvements in nanoparticle signal achieved by novel optical filtering schemes, benchmark them against theory, and provide physical explanations for the signal enhancements. Our refined common-path interferometric microscopy technique provides an overall ten-fold enhancement in the visibility of low-index, non-resonant polystyrene nanospheres (r similar to 25 nm), resulting in nearly 8% signal-to-background ratio. Our method can be a highly sensitive, low-cost, label-free, high-throughput platform for accurate detection and characterization of weakly scattering low-index nanoparticles with sizes ranging from several hundred down to a few tens of nanometers, covering nearly the entire size spectrum of biological particles. (C) 2017 Optical Society of America