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

Abstract

Coherent Raman Scattering (CRS) has emerged in the last decade as a powerful multiphoton microscopy technique offering chemically specific label-free imaging in real time with high three-dimensional spatial resolution. Many technical realizations of CRS microscopy have been proposed to remove, suppress, or account for the non-resonant background in the nonlinear susceptibility which complicates spectral analysis and reduces image contrast. Here, we demonstrate coherent anti-Stokes Raman scattering microscopy using a dual-polarization balanced heterodyne detection in epi-geometry (eH-CARS), providing background-free chemically specific image contrast for nanoparticles and interfaces, shot-noise limited detection, and phase sensitivity. We show the sensitivity and selectivity of eH-CARS in comparison with forward CARS and stimulated Raman scattering on polystyrene beads in agarose gel. As an important biologically relevant application, we demonstrate eH-CARS imaging of individual lipid bilayers with high contrast and topographic sensitivity.