Heterodyne dual-polarization epi-detected CARS microscopy for chemical and topographic imaging of interfaces

摘要

We present a label-free vibrational microscopy technique recently developed by us, which offers backgroundfreechemically-specific image contrast, shot-noise limited detection, and phase sensitivity enabling topographicimaging of interfaces. The technique features interferometric heterodyne detection of coherent anti-Stokes Ramanscattering (CARS) in epi-geometry, as well as multi-modal acquisition of stimulated Raman scattering andforward-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 canresolve a single lipid bilayer, distinct from a double bilayer, and measure the phase of its susceptibility, whichprovides information about the topography of the bilayer with nanometer resolution. As an additional applicationexample, we show imaging of silicon oil droplets surrounded by an aqueous environment at the glass-waterinterface, where three different signal generation pathways are distinguished. Our epi-detected heterodyne CARSmicroscope setup thus paves the way to exciting new experiments pushing the sensitivity and resolution limitsof vibrational microscopy to the nanoscale.