Scott J. Woltman

Liquid crystals : frontiers in biomedical applications

Introduction to Liquid Crystals Basic Optics of Liquid Crystals Display Technologies Medical Displays Liquid Crystals in Spectroscopy, Microscopy and Hyperspectral Imaging Liquid Crystal Biosensors Biomimicking with Liquid Crystals Actuators and Delivery Systems Liquid Crystal Lasers.

Holographic diffraction gratings using polymer-dispersed ferroelectric liquid crystals

By controlling the morphology of holographic polymer-dispersed ferroelectric liquid crystals (FLCs), highly aligned FLC domains are obtained for diffractive optical applications. Rapid, thresholdless switching is observed for various grating pitch sizes between approximately 3 and approximately 12 microm. A simple phenomenological model is presented encompassing a distribution of domain sizes and an effective field that stabilizes the FLC domains to reflect the observed thresholdless switching and optical behavior.

Template induced chiral ordering in nematic liquid crystalline materials : A deuterium nuclear magnetic resonance study

Glancing angle deposition is used to create porous liquid crystal alignment layers with high aspect-ratio, three-dimensional features. We use solid-state deuterium nuclear magnetic resonance to determine the alignment of alpha deuterated 4′-pentyl-4-cyanobiphenyl in a 3.2μm thick SiO2 film comprised of independent, helical structures. Comparing measured spectra with models, we determine that the liquid crystalline molecules exhibit chiral ordering dictated by the features of the template films. In the plane of deposition the liquid crystalline molecules tilt away from the substrate normal at an average angle of 51°, which is commensurate with the helical features of the chiral template.

Tunable cholesteric liquid crystal lasers through in-plane switching

The investigation of dye-doped liquid crystal systems for lasing applications has become a burgeoning topic in recent years. To date, reports have been made of the tunability of cholesteric liquid crystal lasers by means of temperature, photochemical processes and mechanical forces. The application of an in-plane electric field on a cholesteric liquid crystal results in an unwinding and elongation of the cholesteric pitch. This change in pitch length shifts the reflection band of the cholesteric liquid crystal. We report on the tunability of a cholesteric liquid crystal laser in an in-plane switching mode cell. Tunabilities of up to 15 nm have been achieved in these cells. Electrical tuning methods have significant advantages over the other techniques by which cholesteric lasers can be tuned, especially with regards to the potential applications of liquid crystal lasers.

Patterned liquid-crystal laser film for multi-dimensional multi-color emissive film technology

— A two-dimensional array consisting of dye-doped reflection-mode holographic-polymer-dispersed liquid crystal (H-PDLC) lasers with alternating pitch lengths is presented. These post structures each reflect at a narrow bandwidth of light. The addition of laser dye to the H-PDLC system allows for the generation of laser emission at the edge of the reflection band, or photonic band gap. In patterning these H-PDLC post structures, a narrow-linewidth patterned emissive color film is realized. The potential of such films and their implication in the display industry is discussed. In creating a three-color array, an active emissive color film could replace the backlight and color filter components within the display. Such a patterned system would possess a wide color gamut, through spatial color synthesis, formed by narrow-linewidth lasing structures with well-defined wavelengths of emission.

Survey of switchable lasing configurations using structures of liquid crystal and polymer dispersions

We investigate the fabrication of holographic polymer dispersed liquid crystals (H-PDLCs) for use as switchable laser cavities. H-PDLCs are liquid crystal and polymer dispersions used in grating applications for displays, optical communications and optical security. By controlling the pitch of the H-PDLC and the laser dye used, we are able to fabricate a tunable laser. H-PDLCs were made in both reflection and transmission modes to vary the method by which lasing action occurs. The dye-doped H-PDLCs were pumped with nanosecond pulses from a laser with emission at 532 nm and a power of approximately 6 mJ. Lasing action was observed using a spectrometer from the H-PDLC grating; peak wavelengths occurred over a range of wavelengths, depending on the dye used, with the full width of the emission peaks approximately 6-8 nm at half maximum. The lasing action can be turned on and off by the application and removal of an electric field due to the properties of an H-PDLC. Furthermore, we investigate multidimensional architectures and quasicrystal symmetries for lasing applications. Applications for these cells include use in small-scale portable devices requiring a tunable laser source.

Laser Emission from Dye-Doped Liquid Crystal Gratings Formed by Polarization Holography

Laser emission from a nematic liquid crystal system whose grating structure is induced by a linear photopolymerizable alignment layer is reported. The grating structure is written on the alignment layer through polarization holography, inducing periodic boundary conditions on the laser dye-doped nematic liquid crystal. We report on the presence of laser emission at wavelengths predicted by coupled wave theory and the switchability of emission in these systems through the application of an electric field. Sensitivities to incident polarizations are also discussed.

P-119: 2H-NMR Study of Nanohorn Doped Liquid Crystals for Improved Dynamic Response in Liquid Crystal Displays

The doping of liquid crystals with nanotube technology has been shown to improve the electro-optic performance of liquid crystal displays. Here we present a basic study using electro-optic measurements and nuclear magnetic resonance to better understand the underlying phenomenon of this effect and propose a simple phenomenological model.

P‐208L: Late‐News Poster: Liquid Crystal Lasers for Projection Displays

The liquid crystal laser presents itself as an interesting tool for projection displays, acting as the illumination source. Liquid crystal lasers are fast becoming an interesting area of research within the liquid crystal community. In utilizing integrating these systems with current liquid crystal display (LCD) projection systems, novel designs can be envisioned.