The present work introduces a new method that is used to explore the connection between molecular order and molecular dynamics in liquid crystals. In liquid crystals, the building blocks show a liquid like disorder in at least one dimension of space with an otherwise crystalline like positional or orientational long range order. A new microscope is introduced that combines polarization measurements with the ability to track single fluorescent probe molecules in a thin sample of ordered liquid crystal. A new method for the analysis of orientation dependent diffusion is also introduced. It can be used to spatially resolve the anisotropic diffusion of the probe molecules. With this setup, molecular structure and molecular dynamics can be directly compared on a μm scale. Three different kinds of liquid crystal samples are analyzed with the new experimental method. First, twisted nematic liquid crystal cells are used to verify a proposed model for the connection between molecular structure and the dynamics in twisted nematic cells. Second, the liquid crystal structure and probe mobility are analyzed in homogeneous samples in a temperature regulated environment. The third experiment focuses on the combination of both of these scenarios. Different domains in a heterogeneous section of a sample are analyzed with different methodical approaches at various temperatures. The results display the close connection between molecular order and molecular dynamics in the samples. It is also found that the probe molecules introduce local distortions in the director field of the host material. Despite this realization, only the absolute value of the probes mobility seems to be effected. The anisotropy of the translational diffusion of the probe molecules resembles the results found in the literature on the self-diffusion of the liquid crystal molecules. The anisotropy also follows the same temperature dependence as the order of the host molecules. Using these results and the new method of analyzing single molecule tracking data, it is shown that the structure of a heterogeneous sample can be spatially resolved, only by means of single probe molecule tracking.

The present work introduces a new method that is used to explore the connection between molecular order and molecular dynamics in liquid crystals. In liquid crystals, the building blocks show a liquid like disorder in at least one dimension of space with an otherwise crystalline like positional or orientational long range order. A new microscope is introduced that combines polarization measurements with the ability to track single fluorescent probe molecules in a thin sample of ordered liquid crystal. A new method for the analysis of orientation dependent diffusion is also introduced. It can be used to spatially resolve the anisotropic diffusion of the probe molecules. With this setup, molecular structure and molecular dynamics can be directly compared on a μm scale. Three different kinds of liquid crystal samples are analyzed with the new experimental method. First, twisted nematic liquid crystal cells are used to verify a proposed model for the connection between molecular structure and the dynamics in twisted nematic cells. Second, the liquid crystal structure and probe mobility are analyzed in homogeneous samples in a temperature regulated environment. The third experiment focuses on the combination of both of these scenarios. Different domains in a heterogeneous section of a sample are analyzed with different methodical approaches at various temperatures. The results display the close connection between molecular order and molecular dynamics in the samples. It is also found that the probe molecules introduce local distortions in the director field of the host material. Despite this realization, only the absolute value of the probes mobility seems to be effected. The anisotropy of the translational diffusion of the probe molecules resembles the results found in the literature on the self-diffusion of the liquid crystal molecules. The anisotropy also follows the same temperature dependence as the order of the host molecules. Using these results and the new method of analyzing single molecule tracking data, it is shown that the structure of a heterogeneous sample can be spatially resolved, only by means of single probe molecule tracking.

As dental caries is one of the most common diseases, the early and noninvasive detection of carious lesions plays an important role in public health care. Optical coherence tomography (OCT) with its ability of depth-resolved, high-resolution, noninvasive, fast imaging has been previously recognized as a promising tool in dentistry. Additionally, polarization sensitive imaging provides quantitative measures on the birefringent tissue properties and can be utilized for imaging dental tissue, especially enamel and dentin. By imaging three exemplary tooth samples ex vivo with proximal white spot, brown spot, and cavity, we show that the combination of polarization sensitive OCT and the degree of polarization uniformity (DOPU) algorithm is a promising approach for the detection of proximal carious lesions due to the depolarization contrast of demineralized tissue. Furthermore, we investigate different sizes of the DOPU evaluation kernel on the resulting contrast and conclude a suitable value for this application. We propose that DOPU provides an easy to interpret image representation and appropriate contrast for possible future screening applications in early caries diagnostics.

Since optical coherence tomography (OCT) provides three-dimensional high-resolution images of biological tissue, the benefit of polarization contrast in the field of dentistry is highlighted in this study. Polarization-sensitive OCT (PS OCT) with phase-sensitive recording is used for imaging dental and mucosal tissues in the human oral cavity in vivo. An enhanced polarization contrast of oral structures is reached by analyzing the signals of the co- and crosspolarized channels of the swept source PS OCT system quantitatively with respect to reflectivity, retardation, optic axis orientation, and depolarization. The calculation of these polarization parameters enables a high tissue-specific contrast imaging for the detailed physical interpretation of human oral hard and soft tissues. For the proof-of-principle, imaging of composite restorations and mineralization defects at premolars as well as gingival, lingual, and labial oral mucosa was performed in vivo within the anterior oral cavity. The achieved contrast-enhanced results of the investigated human oral tissues by means of polarizationsensitive imaging are evaluated by the comparison with conventional intensity-based OCT.