In this paper we present the work performed by AlphaMicron in the area of Adaptive Window application
using a guest-host liquid crystal configuration combined with liquid crystal based solar concentrator and high
efficiency photovoltae. The system can be used for Zero-Energy Building applications by providing a
dynamic solar heat gain coefficient. This allows the reduction of the energy loss through windows in mixed
Cholesteric liquid crystals, because of their birefringence and periodic structure, and 1-d photonic band-gap materials. In the reflection band, classical light propagation is forbidden for one of the two eigenmodes; for this mode, the material acts as a distributed cavity host. This inherent distributed cavity effect modifies the fluorescence spectrum, and, if the material is optically pumped, allows population inversion and mirrorless lasing. We have studied emission from thin samples of liquid crystalline materials optically pumped by pico- and nanosecond laser pulses. We have observed laser emission, without an external cavity, from dye-doped liquid crystals, from pure cholesteric liquid crystals without dyes, and from cholesteric liquid crystal elastomers. We present the results of these experiments, discuss the relation between material properties and the lasing process, and consider promising materials and applications.
Increasing interest in helmet-mounted displays (HMDs) has fueled research in variable transmittance visors (VTVs) because a VTV can reduce glare and increase HMD contrast in bright lighting conditions. The ideal VTV will be an electrically controllable light valve that allows the pilot to adjust visor transmittance (tint) to the level appropriate to the ambient lighting conditions. Liquid- crystal based devices can provide an efficient method for accomplishing this. Because flight helmets utilize polycarbonate visors, VTVs must be implemented on complex curved, plastic substrates. Liquid crystal devices, however, are typically implemented on flat glass substrates. We present a novel system, Variable Attenuation Liquid Crystal Device (VALiD), which can be utilized for this application. VALiD is a dichroic dye and liquid crystal based guest-host system. Our specific configuration allows for a fast system that fails to the clear state. Furthermore, the degree of polarization dependence can be tailored for use in different applications. VALiD has been implemented on thin, flexible, flat plastic substrates. Recently, this has been extended to doubly curved polycarbonate substrates and a prototype has been fabricated. In this paper we present the characteristics of this technology.
Bistable reflective cholesteric displays offer a solution for low power consumption displays. Image retention in zero field combined with inherent reflectivity (no need for backlighting) makes them ideal for applications such as portable document viewers. Here, we present an overview of the current research activities and achievements in this technology with focus on recent developments in white-on-black and stacked color displays, low cost drive electronics, video rate potential, and newly developed field induced polymer walls.
A variety of spectroscopic techniques has been used to study the optical properties of epitaxial GaN based materials grown by metalorganic chemical vapor deposition and molecular beam epitaxy. The emphasis was on the issues vital to device applications such as stimulated emission and laser action, as well as carrier relaxation dynamics. Sharp exciton structures were observed by optical absorption measurements above 300 K, providing direct evidence of the formation of excitons in GaN at temperatures higher than room temperature. Using a picosecond streak camera, the time decay of free and bound exciton emissions was studied. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. In addition, the optical nonlinearity of GaN was studied using wave mixing techniques.
Nonlinear optical and carrier dynamics of CdMnSe and CdMnTe were studied using picosecond pulses from a mode-locked, Q-switched Nd:YAG laser operating at 1064 nm. The study of the effects of free carriers on the refraction and absorption of a delayed probe beam resulted in the determination of the magnitude and sign of these nonlinearities for different Mn concentrations. It was found that at high carrier concentrations the magnitude of the nonlinear refraction coefficient is not constant and decreases with an increase in the electron concentration. The carrier dynamics were studied using forward propagating pulsed probe degenerate four wave mixing. The study was done for a number of different pump beam irradiances. A saturation in the diffraction efficiency was found at higher carrier concentrations. The lifetime of the electrons in the conduction band was determined by monitoring the lifetime of the free carrier absorption.
This paper summarizes recent results obtained on CdTe polarization rotation switches and optical limiter based on lead glasses. The polarization rotation switch is based on picosecond pulse four wave mixing with two beams and the switching characteristics are dependent on beam crossing angle, relative polarization directions, and pulse timing. Material enhancement of the nonlinear scattering is demonstrated by using Mn-doped crystals. Optical limiting by thermal lensing on the nanosecond time scale was characterized in a variety of lead based glasses and it was found that the main contribution to the thermo-optic coefficient is due to thermally induced changes in the electronic polarizability of the glass components (especially oxygen) and is effected by the polarizing power of the network former ions. Random network structures have greater thermo—optic coefficients than ring and chain structures and modifier ions affect the properties through changes in the absorption coefficient of the material.