Figure 2
From: Orientational Mapping Augmented Sub-Wavelength Hyper-Spectral Imaging of Silk
(a) Four-polarisation method in IR absorbance at different polarisation azimuths, A = f(Θ)32, which was used to determine the orientational anisotropy in far-field FT-IR measurements. (b) An optical image of a concentric 2-μm-period Au grating (with a duty cycle of 0.5) on a cover glass used for reflection FT-IR imaging carried out with a Cassegrainian objective lens with a focusing cone over a 17-to −30° range; dashed-line marks the top-view of the incidence plane. The diameter of the circular grating was 0.5 mm. Four reflection maps for a linearly polarised incidence at the specified polarisation angle (schematically also marked by arrows) at 1500 cm−1 (~6.7 μm) wavelength (Spotlight, PerkinElmer); IR,0 are the reflected and incidence intensities, respectively. (c) In-house developed ATR accessory for Hyperion 2000, Bruker microscope. Inset shows schematic illustration of optical geometry used in the ATR FT-IR measurement with a 100-μm diameter Ge tip (refractive index n = 4).
