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Light interacts with liquid crystals. It is one of the most useful tools that can reveal the director field of liquid crystals, which can be either uniform or spatially varied. On the other hand, liquid crystals can also be used to control the photon current which is light. In this dissertation, the complementary relation between light and liquid crystals is explored.Understanding the behavior of nematics in inhomogeneous external fields is of fundamental interest. The director field of a nematic sample in radially varying magnetic field was studied experimentally by interferometry and theoretically by modeling and numerics. Experimental studies involved recording far-field interference patterns using coherent polarized light. The magnetic field was described analytically, and the director configuration and the interference pattern in the far field were modeled numerically. A comparison of the experimentally determined and the numerically calculated far-field patterns was made.The optical, dielectric and thermal properties of cholesterics were studied, including their bandgap structure. These experimental results were useful for developing an optical device: an optical transistor and realizing distributed feedback lasing, which were both demonstrated in this work. Light carries momentum and energy. The energy can be harvested to do mechanical work directly and indirectly. There are many advantages of converting the light energy directly to mechanical work. Two photomechanical systems were studied in this work; liquid crystal elastomer and molecular crystals.Based on the way nematics modify light, a tunable waveplate using nematics was constructed which can be adjusted by controlling the director field. This waveplate is one of the key components in the optical transistor.Another goal of this work is to use one light beam to control liquid crystals in order to control an other beam of light. The optical transistor has two components; the tunable waveplate and a cholesteric film. The optical transistor is similar to traditional transistors using one current to control another. However, the optical transistor is using photon current to control another photon current rather than electric current. The controlling light can manipulate retardation of the waveplate or the reflection band of the cholesteric film, and indirectly control the intensity of the light transmitted through these two components.The liquid crystal laser is made using dye-doped cholesterics. In the lasing sample, the cholesteric liquid crystal with a selective reflection band serves as a distributed feedback cavity. The fluorescent dye with emission wavelength within the reflection band provides gain. Lasing occurs at the band edges on pumping the sample with a pulsed laser above the threshold. |
