It is difficult to fabricate electrode, which have gradient electric field from edge to center by applying voltage. In this study, a gradient refractive index profile can be easily formed. We change the experimental parameter about exposure time of UV light, concentration of PVK film and the Cell gap to investigate the influence on focal length. As the exposure time increase, the differences in conductivity become large from edge to center, which create better index distribution. For high concentration of PVK films, UV light can not effectively improve the conductivity of transmittance zone, which case the worse index distribution. The increasing of cell gap resulting in poor distribution of the refractive index, which cause larger focal length.

In this study, a double-ellipsoid structure is proposed for measurements of optical properties of liquid-crystal displays (LCDs). By using the double-ellipsoid structure, light dispersion and measurement time, which occurs during the measurement of optical properties of LCDs, can be greatly reduced. The system also significantly decreases reflective loss on interface, increasing the accuracy of the measurement. Moreover, by using the conoscopy measured from the proposed structure, light distribution of the dark state along off-axis direction can be analyzed. Based on the analysis, the cell gap and pretilt angle of vertical alignment liquid-crystals (VA-LCs) are evaluated. The proposed structure, which exhibits a fast and high accuracy measurement, is highly promising for future optical measurement of LCDs.

This thesis establishes methods to locally and effciently detect the fluorescence from photonic crystals (PCs) in dependence on wavelength and direction. These are applied to three dimensional (3D) PCs grown by vertical deposition of polystyrene beads. The experiments allow conclusions about the local 3D structure of a sample, about defects in its volume and about spatial structural variations. They thus provide more information than typical spectroscopy measurements that average over large areas and methods that only image the surface structure like scanning electron microscopy. A focused laser is used to excite emitters in the sample only locally. The fluorescence is then collected by a microscope objective. Every point in this objective’s back focal plane (BFP) corresponds to a certain direction. This property is utilized in two ways. When observing a small spectral range of the emission in the BFP, stop bands appear as intensity minima since they hinder the emission into the corresponding directions. Thus, back focal plane imaging (BFPI) allows to visualize stop bands of many directions at the same time. The detected patterns permit to find the in-plane and out-of-plane orientation of the PC lattice and to conclude on the presence of stacking faults. Spatial variations of the structure are observed on a length scale of a few micrometers. The depth of the stop band is reduced at sample positions, where structural changes occur. In back focal plane spectroscopy (BFPS), a slit selects light from certain points in the BFP, which is spectrally dispersed subsequently. This allows to record spectra from many directions simultaneously. From them, a lattice compression along the sample normal of about 4% is found. Small deformations are also observed for other directions. Scattering at defects redistributes the emission. This increases the detected intensity compared to homogeneous media at some stop band edges in a broad spectral range for samples thicker than the scattering mean free path. Thinner samples show a narrow enhancement due to an increase in the fractional density of optical states and thus in emission. BFPI and BFPS are also used to observe the growth of PCs from drying droplets. The experiments show that the beads initially form a non-close packed lattice. This causes stress as the lattice constant decreases, which is released by cracking of the PCs.

No description available.

Dans une première partie de cette thèse, nous avons étudié le comportement sous champ électrique de la séquence de phases des "cristaux liquides smectiques chiraux" en développant une étude sous champ électrique (E) et en fonction de la température (T) qui sont deux variables thermodynamiques indépendantes. Les résultats de mesures ont conduit au tracé des diagrammes de phase Champ électrique-Température (E-T). Ces diagrammes peuvent dans certains cas révéler l'induction sous champ électrique de nouvelles phases n'existant pas à champ nul. D'autre part, suite à l'étude de certains composés présentant la phase ferroélectrique SmC* dans leur séquence de phase à champ nul. Le tracé de leurs diagrammes de phases (E-T) a permis de mettre en évidence un problème de coexistence entre une phase paraélectrique et une autre ferroélectrique. Pour bien localiser cette séquence de phases sans rencontrer ce phénomène de démixtion, on a fait appel à une nouvelle étude optique sans champ électrique basée sur la méthode de conoscopie à balayage. L'analyse de l'ellipticité de la lumière transmise en fonction de la rotation de l'échantillon a donné accès aux deux indices de réfraction (ne et no) séparément, à la biréfringence (?n), au pouvoir rotatoire optique (PRO) et à la gyrotropie. Ces études que nous avons développé avec succès nous permettent une mise au point robuste et efficace des comportements des différentes phases de cristaux liquides smectiques chiraux sous et en absence du champ électrique. / In the first part of this thesis, we studied the behavior of the phase sequence of "smectic chiral liquid crystals" in order to develop a study under electric field (E) and as a function of tempertaure (T) which are two independent thermodynamic variables. The measurement results allow us to establish the electric field versus temperature phase diagram (E-T). In some cases, the phase diagram, under electric field, can reveal the induction of new phase which is not existing at zero field. On the other hand, we investigated certain compounds with ferroelectric phase SmC* in their phase sequence at zero field. The delimitation of phase diagrams (E-T) helped to highlight a coexistence problem between a paraelectric phase and a ferroelectric one. To locate this phase sequence without encountering this demixing phenomenon, we used a new optical study without electric field based on scanning conoscopy method. The analysis of the ellipticity of the transmitted light depending on the rotation of the sample gave access to the two refractive indices (ne and no) seperately, the birefringence (?n), the optical rotatory power (ORP) and the gyrotropy. These studies that we have successfully developed enable us to develop a robust and effictive behavior of different phases of chiral smectic liquid crystals under and without electric field.

This thesis establishes methods to locally and effciently detect the fluorescence from photonic crystals (PCs) in dependence on wavelength and direction. These are applied to three dimensional (3D) PCs grown by vertical deposition of polystyrene beads. The experiments allow conclusions about the local 3D structure of a sample, about defects in its volume and about spatial structural variations. They thus provide more information than typical spectroscopy measurements that average over large areas and methods that only image the surface structure like scanning electron microscopy. A focused laser is used to excite emitters in the sample only locally. The fluorescence is then collected by a microscope objective. Every point in this objective’s back focal plane (BFP) corresponds to a certain direction. This property is utilized in two ways. When observing a small spectral range of the emission in the BFP, stop bands appear as intensity minima since they hinder the emission into the corresponding directions. Thus, back focal plane imaging (BFPI) allows to visualize stop bands of many directions at the same time. The detected patterns permit to find the in-plane and out-of-plane orientation of the PC lattice and to conclude on the presence of stacking faults. Spatial variations of the structure are observed on a length scale of a few micrometers. The depth of the stop band is reduced at sample positions, where structural changes occur. In back focal plane spectroscopy (BFPS), a slit selects light from certain points in the BFP, which is spectrally dispersed subsequently. This allows to record spectra from many directions simultaneously. From them, a lattice compression along the sample normal of about 4% is found. Small deformations are also observed for other directions. Scattering at defects redistributes the emission. This increases the detected intensity compared to homogeneous media at some stop band edges in a broad spectral range for samples thicker than the scattering mean free path. Thinner samples show a narrow enhancement due to an increase in the fractional density of optical states and thus in emission. BFPI and BFPS are also used to observe the growth of PCs from drying droplets. The experiments show that the beads initially form a non-close packed lattice. This causes stress as the lattice constant decreases, which is released by cracking of the PCs.