We present a label-free vibrational microscopy technique recently developed by us, which offers backgroundfree chemically-specific image contrast, shot-noise limited detection, and phase sensitivity enabling topographic imaging of interfaces. The technique features interferometric heterodyne detection of coherent anti-Stokes Raman scattering (CARS) in epi-geometry, as well as multi-modal acquisition of stimulated Raman scattering and forward-emitted CARS intensity in the same instrument. As an important biologically-relevant application, epi-detected heterodyne CARS imaging of individual lipid bilayers is demonstrated. We show that we can resolve a single lipid bilayer, distinct from a double bilayer, and measure the phase of its susceptibility, which provides information about the topography of the bilayer with nanometer resolution. As an additional application example, we show imaging of silicon oil droplets surrounded by an aqueous environment at the glass-water interface, where three different signal generation pathways are distinguished. Our epi-detected heterodyne CARS microscope setup thus paves the way to exciting new experiments pushing the sensitivity and resolution limits of vibrational microscopy to the nanoscale.

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Wolfgang Langbein, Dafydd Sion Harlow, David Regan, Iestyn Pope, and Paola Borri, "Heterodyne dual-polarization epi-detected CARS microscopy for chemical and topographic imaging of interfaces," Proc. SPIE 10890, Label-free Biomedical Imaging and Sensing (LBIS) 2019, 1089003 (Presented at SPIE BiOS: February 02, 2019; Published: 4 March 2019); https://doi.org/10.1117/12.2507636.