Liquid crystals (LCs) are a state of matter which has properties between those of conventional liquids and those of solid crystals. For instance, a liquid crystal may flow like a liquid, but its molecules may be oriented in a crystal-like way. There are many different types of liquid-crystal phases, which can be distinguished by their different optical properties. The contrasting areas in the textures correspond to domains where the liquid-crystal molecules are oriented in different directions. Within a domain, however, the molecules are well ordered. LC materials may not always be in a liquid-crystal phase.
In solid-state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference between the top of the valence band and the bottom of the conduction band in insulators and semiconductors. It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current. It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow. Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.
Sajeev John, OC, FRSC is a Professor of Physics at the University of Toronto and Canada Research Chair holder.
This article is about ionizing radiation detectors. For information about semiconductor detectors in radio, see Detector (radio), Crystal detector, Diode#Semiconductor diodes, and Rectifier.
Photonic-crystal fiber (PCF) is a class of optical fiber based on the properties of photonic crystals. It was first explored in 1996 at University of Bath, UK. Because of its ability to confine light in hollow cores or with confinement characteristics not possible in conventional optical fiber, PCF is now finding applications in fiber-optic communications, fiber lasers, nonlinear devices, high-power transmission, highly sensitive gas sensors, and other areas. More specific categories of PCF include photonic-bandgap fiber, holey fiber, hole-assisted fiber, and Bragg fiber. Photonic crystal fibers may be considered a subgroup of a more general class of microstructured optical fibers, where light is guided by structural modifications, and not only by refractive index differences.
A distributed Bragg reflector (DBR) is a reflector used in waveguides, such as optical fibers. It is a structure formed from multiple layers of alternating materials with varying refractive index, or by periodic variation of some characteristic of a dielectric waveguide, resulting in periodic variation in the effective refractive index in the guide. Each layer boundary causes a partial reflection of an optical wave. For waves whose vacuum wavelength is close to four times the optical thickness of the layers, the many reflections combine with constructive interference, and the layers act as a high-quality reflector. The range of wavelengths that are reflected is called the photonic stopband. Within this range of wavelengths, light is "forbidden" to propagate in the structure.
An optical waveguide is a physical structure that guides electromagnetic waves in the optical spectrum. Common types of optical waveguides include optical fiber and rectangular waveguides.
A liquid crystalline mesophase is called lyotropic if formed by dissolving an amphiphilic mesogen in a suitable solvent, under appropriate conditions of concentration, temperature and pressure. A mixture of soap and water is an everyday example of a lyotropic liquid crystal.
A blue phase mode LCD is a liquid crystal display (LCD) technology that uses highly twisted cholesteric phases in a blue phase. It was first proposed in 2007 to obtain a better display of moving images with, for example, frame rates of 100–120 Hz to improve the temporal response of LCDs. This operational mode for LCDs also does not require anisotropic alignment layers and thus theoretically simplifies the LCD manufacturing process.
The Isaac Newton Medal is a gold medal awarded annually by the Institute of Physics accompanied by a prize of £1,000. The award is given to a physicist, regardless of subject area, background or nationality, for outstanding contributions to physics. The award winner is invited to give a lecture at the Institute.. This medal was recently renamed by IoP as the "International Medal".
The IEEE Photonics Award is a Technical Field Award established by the IEEE Board of Directors in 2002. This award is presented for outstanding achievements in photonics, including work relating to: light-generation, transmission, deflection, amplification and detection and the optical/electro-optical componentry and instrumentation used to accomplish these functions. Also included are storage technologies utilizing photonics to read or write data and optical display technologies. It also extends from energy generation/propagation, communications, information processing, storage and display, biomedical and medical uses of light and measurement applications.
Nonlinear photonic crystals are usually used as quasi-phase-matching materials. They can be either one-dimensional or two-dimensional.
A seismic metamaterial, is a metamaterial that is designed to counteract the adverse effects of seismic waves on artificial structures, which exist on or near the surface of the earth. As of 2009 seismic metamaterials were still in the development stage.
A liquid-crystal laser is a laser that uses a liquid crystal as the resonator cavity, allowing selection of emission wavelength and polarization from the active laser medium. The lasing medium is usually a dye doped into the liquid crystal. Liquid-crystal lasers are comparable in size to diode lasers, but provide the continuous wide spectrum tunability of dye lasers while maintaining a large coherence area. The tuning range is typically several tens of nanometers. Self-organization at micrometer scales reduces manufacturing complexity compared to using layered photonic metamaterials. Operation may be either in continuous wave mode or in pulsed mode.
Structural coloration is the production of colour by microscopically structured surfaces fine enough to interfere with visible light, sometimes in combination with pigments. For example, peacock tail feathers are pigmented brown, but their microscopic structure makes them also reflect blue, turquoise, and green light, and they are often iridescent.
Costas M. Soukoulis is a Senior Scientist in the Ames Laboratory and a Distinguished Professor of Physics at Iowa State University. He received his B.Sc. from University of Athens in 1974. He obtained his Ph.D. in Physics from the University of Chicago in 1978. From 1978 to 1981 he was at the Physics Department at University of Virginia. He spent 3 years (1981–84) at Exxon Research and Engineering Co. and since 1984 has been at Iowa State University (ISU) and Ames Laboratory. He has been an associated member of IESL-FORTH at Heraklion, Crete, Greece since 1984.
A nanophotonic resonator or nanocavity is an optical cavity which is on the order of tens to hundreds of nanometers in size. Optical cavities are a major component of all lasers, they are responsible for providing amplification of a light source via positive feedback, a process known as amplified spontaneous emission or ASE. Nanophotonic resonators offer inherently higher light energy confinement than ordinary cavities, which means stronger light-material interactions, and therefore lower lasing threshold provided the quality factor of the resonator is high. Nanophotonic resonators can be made with photonic crystals, silicon, diamond, or metals such as gold.
Nanoholes are a class of nanostructured material consisting of nanoscale voids in a surface of a material. Not to be confused with nanofoam or nanoporous materials which support a network of voids permeating throughout the material, nanohole materials feature a regular hole pattern extending through a single surface. These can be thought of as the inverse of a nanopillar or nanowire structure.
