No description available.

Master´s thesis covers introduction to the problems of materials with specific proprieties named liquid crystals. Theoretic part features primary fission these materials, theirs mechanical, electrotechnical and optical characteristics. Interesting chapter is description choice application including perhaps most interesting using liquid crystals - liquid crystal display. In this trend continues experimental part too, where there are first mentioned characteristics LCD, and after it alone metering capacitive characteristics display with active matrix. Main attention in experiment is however concentraded on evaluation frequency analysis of components complex permittivity regarding in plant temperature on submitted sample liquid crystals.

L’objectif de cette thèse est de réaliser une peau active pour le camouflage de véhicule terrestre à base de la technologie cristal liquide cholestérique. Après analyse de l’environnement, une texture est appliquée sur les écrans cristaux liquides afin de réduire la signature visuelle et thermique du véhicule. Les travaux ont consisté à proposer un dispositif trichrome cristal liquide permettant d’obtenir la colorimétrie définie par le cahier des charges. Les problèmes de tenue en température, de réflexion spéculaire, de niveaux de gris, niveaux de réflectivité, de réduction des tensions appliquées ont été traités au cours de cette thèse. La technologie proposée a permis la réalisation d’un démonstrateur sur un robot télécommandé qui a été présenté au salon Eurosatory 2018 sur le stand du ministère des armées. Des travaux ont été également engagés pour le développement de modulateur optique dans l’infrarouge, à base de cristaux liquides cholestérique, afin de moduler la réflectivité et donc de pouvoir limiter la signature thermique du véhicule. Plusieurs pistes ont été testées et proposées. / The objective of this thesis is to achieve an active skin for the camouflage of a land vehicle based on cholesteric liquid crystal technology. After analysis of the environment, a texture is applied on the LCDs to reduce the visual and thermal signature of the vehicle. The work consisted of proposing a trichrome liquid crystal device to obtain the colorimetry defined by the specifications. The problems of temperature resistance, specular reflection, gray scale, reflectivity levels, reduction of applied voltages were discussed during this thesis. The proposed technology enabled to realization of a demonstrator on a remote controlledrobot that was presented at Eurosatory 2018 on the stand of the Ministry of the Armed Forces. Work has also been started on the development of optical modulators in the infrared, based on cholesteric liquid crystals, in order to modulate the reflectivity and thus to be able to limit the thermal signature of the vehicle. Several tracks have been tested and proposed.

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 generation and application of human stem-cell-derived functional neural circuits promises novel insights into neurodegenerative diseases. These networks are often studied using stem-cell derived random neural networks in vitro, with electrical stimulation and recording using multielectrode arrays. However, the impulse response function of networks is best obtained with spatiotemporally well-defined stimuli, which electrical stimulation does not provide. Optogenetics allows for the functional control of genetically altered cells with light stimuli at high spatiotemporal resolution. Current optogenetic investigations of neural networks are often conducted using full field illumination, potentially masking important functional information. This can be avoided using holographically shaped illumination. In this article, we present a digital holographic illumination setup with a spatial resolution of about 8 µm, which suffices for the stimulation of single neurons, and offers a temporal resolution of less than 0.6 ms. With this setup, we present preliminary single-cell stimulation recording of stem-cell derived induced human neurons in a random neural network. This will offer the opportunity for further studies on connectivity in such networks.

No description available.

No description available.

Blue phase liquid crystals (BPLCs) have a delicate lattice structure existing between chiral nematic and isotropic phases, with a stable temperature range of about 2 K. But due to short coherent length, these self-assembled nano-structured BPLCs have a fast response time. In the past three decades, the application of BPLC has been rather limited because of its narrow temperature range. In 2002, Kikuchi et al. developed a polymer stabilization method to extend the blue-phase temperature range to more than 60 K. This opens a new gateway for display and photonic applications. In this dissertation, I investigate the material properties of polymer-stabilized BPLCs. According the Gerber’s model, the Kerr constant of a BPLC is linearly proportional to the dielectric anisotropy of the LC host. Therefore, in the frequency domain, the relaxation of the Kerr constant follows the same trend as the dielectric relaxation of the host LC. I have carried out experiments to validate the theoretical predictions, and proposed a model called extended Cole-Cole model to describe the relaxation of the Kerr constant. On the other hand, because of the linear relationship, the Kerr constant should have the same sign as the dielectric anisotropy of the LC host; that is, a positive or negative Kerr constant results from positive (∆ε > 0) or negative host LCs (∆ε < 0), respectively. BPLCs with a positive Kerr constant have been studied extensively, but there has been no study on negative ∆ε polymer-stabilized BPLCs. Therefore, I have prepared a BPLC mixture using a negative ∆ε LC host and investigated its electro-optic properties. I have demonstrated that indeed the induced birefringence and Kerr constant are of negative sign. Due to the fast response time of BPLCs, color sequential display is made possible without color breakup. By removing the spatial color filters, the optical efficiency and resolution density are both tripled. With other advantages such as alignment free and wide viewing angle, polymer-stabilized BPLC is emerging as a promising candidate for next-generation displays. However, the optical efficiency of the BPLC cell is relatively low and the operating voltage is quite high using conventional in-plane-switching electrodes. I have proposed several device structures for improving the optical efficiency of transmissive BPLC cells. Significant improvement in transmittance is achieved by using enhanced protrusion electrodes, and a 100% transmittance is achievable using complementary enhanced protrusion electrode structure. For a conventional transmissive blue phase LCD, although it has superb performances indoor, when exposed to strong sunlight the displayed images could be washed out, leading to a degraded contrast ratio and readability. To overcome the sunlight readability problem, a common approach is to adaptively boost the backlight intensity, but the tradeoff is in the increased power consumption. Here, I have proposed a transflective blue phase LCD where the backlight is turned on in dark surroundings while ambient light is used to illuminate the displayed images in bright surroundings. Therefore, a good contrast ratio is preserved even for a strong ambient. I have proposed two transflective blue phase LCD structures, both of which have single cell gap, single gamma driving, reasonably wide view angle, low power consumption, and high optical efficiency. Among all the 3D technologies, integral imaging is an attractive approach due to its high efficiency and real image depth. However, the optimum observation distance should be adjusted as the displayed image depth changes. This requires a fast focal length change of an adaptive lens array. BPLC adaptive lenses are a good candidate because of their intrinsic fast response time. I have proposed several BPLC lens structures which are polarization independent and exhibit a parabolic phase profile in addition to fast response time. To meet the low power consumption requirement set by Energy Star, high optical efficiency is among the top lists of next-generation LCDs. In this dissertation, I have demonstrated some new device structures for improving the optical efficiency of a polymerstabilized BPLC transmissive display and proposed sunlight readable transflective blue-phase LCDs by utilizing ambient light to reduce the power consumption. Moreover, we have proposed several blue-phase LC adaptive lenses for high efficiency 3D displays.

No description available.

No description available.