Fig. 2: vSFG microscopy images.
a Schematic of the phase-resolved vSFG microscope showing the input beams (red), lipid monolayer sample (similar to that shown in Fig. 1b) and the objective. Two coordinate systems are defined, the first (x, y, z) being the sample frame, and the second (x', y', z') being the laboratory frame that is defined based on the plane of incidence of the input beams. b vSFG microscopy images of the (R)-DPPC/(R)-POPC monolayer at select frequencies. The frequencies are given in the top-right of each image and correspond to the dashed lines shown in the spectra, and the image amplitudes all correspond to the imaginary part of \({\chi }^{\left(2\right)}\) given in arbitrary units and based on the colour bar shown on the right. c vSFG spectra averaged over all domains (red), outside the domains (blue) and the entire image (black, dashed line). Only the imaginary (absorptive) parts of the phase-resolved responses are shown. The main CH2 and CH3 vibrational resonances are also indicated (with CH3 labels in red and CH2 in green to coincide with the colours used in the molecular stick structure shown in Fig. 1c). SS symmetric stretch, AS antisymmetric stretch, FR Fermi resonance.
