Figure 3. a) Images of azimuthal ss- and sp-polarized IR-DCP transmission and absolute phase spectra. Tsp exhibits a baseline value of 1 in the absence of anisotropy (e.g., for azimuthal sample rotations of 0° and 90°) due to the spectral normalization to a measurement without a sample. b) Azimuthal variation of the C–O–C band height in the absolute ss- and pp-polarized phases as well as their difference.
The parallel-polarized Tss and Δssimages capture all vibrational contributions along the ss polarization axis and therefore also include isotropic contributions. In contrast, the cross-polarized Tsp and Δsp images are only sensitive to signals from anisotropic contributions, qualifying them for the direct inspection of anisotropies. The anisotropic absorption behavior of the nanofibers is directly identified in the cross-polarized images, which show band maxima at 45° azimuthal angle, in agreement with maximum in-plane p–s anisotropy for aligned nanofibers. The parallel-polarized Δss phase image shows azimuthally homogeneous areas beside the vibrational band contributions, which could potentially be used as a measure of optical thickness.
Figure 3 (b) shows the azimuthal variation of the C–O–C band heights in the ss- and pp-polarized phase spectra as well as their difference. Classical FTIR polarimetry cannot measure absolute phases, but only relative ones. In contrast, IR-DCP can separate the information encoded in the polarization-dependent absolute phases.
In summary, the spectral polarimetric amplitudes and phases simultaneously provide complementary information on sample structure and thickness. Moreover, IR-DCP acquires absolute phase data for arbitrary polarization configurations, allowing, for instance, the direct measurement of Δsp without the need for rotating optical elements such as polarizers. Fast sample imaging applications of parallel- and cross-polarized band amplitude and phase properties thus become available in the mid­­­‑IR spectral range.