Fig. 3: Rotational analysis of vSFG microscopy images.
a Schematic of the rotational analysis procedure showing the variation in CH2 (green) and CH3 (red) transition dipoles upon sample rotation (indicated by blue arrows). b Schematic representations of the four-dimensional dataset that is generated, with SFG microscopy images at different spectral frequencies (ω) recorded at multiple azimuthal sample rotations (φ). The change in sample frame coordinates (x, y, z) relative to the laboratory coordinates (x', y', z') upon rotation is explicitly shown, demonstrating the need for back-rotation of the obtained images. c Imaginary part of the out-of-plane spectrum extracted from the magnitude of the 0-fold azimuthal frequency, averaged over all domain regions. d Imaginary part of the in-plane spectrum extracted from the magnitude of the 1-fold azimuthal frequency, averaged over all domain regions. Also shown in the lower parts of panels c, d are the deconvolutions of the spectra into their constituent bands, with CH2 resonances highlighted in green and labelled, CH3 resonances in red and labelled, and unassigned bands in blue. e Magnitude images (in the sample frame) of the CH2 and CH3 resonances at the 0-fold (out-of-plane) and 1-fold (in-plane) azimuthal frequencies. The images are obtained by summing across the frequency regions of the CH2 and CH3 bands and are shown based on the colour scales given on the right, given in arbitrary units. White contour outlines based on the out-of-plane CH3 amplitudes are included in all images to highlight the domain locations. The depicted surface region is part of a wider image common to all rotations, as shown in Fig. 4a.
