Blue phases photonics

The radiative transitions of the previous descriptions have all been spontaneous Relaxation from the excited state to the ground state and emission of photons occur without external aid. In contrast, a stimulated emission occurs when the half-life of the excited state is relatively long, and relaxation can occur only through the aid of a stimulating photon. In stimulated emission, the emitted photon has the same direction as, and is in phase with, the stimulating photon. The example of Cr +-doped AI2O3 that we utilized earlier for our description of the color of ruby works equally well for a description of stimulated emission. Recall that the presence of chromium in alumina alters the electronic structure, creating a metastable state between the valence and conduction bands. Absorption of a blue-violet photon results in the excitation of an electron from... 

Keywords Blue phase Frustration Double twist Electrooptic effect Photonic crystal... 

Chirality is also an important aspect of liquid crystals. The introduction of chiral moieties into the chiral smectic phases induces functions such as ferroelectricity and antiferroelectricity. A few of the unconventional chiral liquid crystals are described in Chapter 1. The blue phase is one of the exotic chiral liquid crystalline phases. In Chapter 3, Kikuchi introduces the basic aspects and recent progress in research of the blue phase. Recently, the materials exhibiting the blue phases have attracted attention because significant photonic and electro-optic functions are expected from the materials. 

LC phase, while the later systems are based on chirality amplification mechanism. There are many types of chiral LC phases such as cholesteric (N ), chiral smectic (Sm ), blue phase (BP), and twist grain boundary (TGB) phase. Among them, N and SmC phases are the most studied due to their potential technological applications. BPs are also receiving increasing attention due to their interesting 3D cubic structures and potential applications as 3D photonic crystals. 

W. Cao, A. Munoz, P. Palffy-Muhoray, B. Taheri, Lasing in a three-dimensional photonic crystal of the liquid crystal blue phase 11. Nat. Mater. 1, 111-113 (2002)... 

It should be noted that the appearance of the cholesteric phase of Reinitzer was different from the appearance of the classical cholesteric phase shown in Fig. 1.3b. The phase was opaque and had blue tint. It took a century to decipher its structure it appears to be a blue phase (see Chapter 4) with a structure of liquid lattice consisting exclusively of defects of an initially ideal helical structure. This phase is periodic and shows Bragg diffractiMi of light in all the three principal directions. Therefore, Reinitzer has discovered the first generic photonic crystal At present, a study of photonic crystals, mostly artificial, is one of the hot topics in physics [8]. 

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

With each chapter is designed to be self-contained, the first chapters cover the basic physics of liquid crystals, their interaction with light and electric fields, and the means by which they can be modelled. Next arc described the majority of the ways in which liquid crystals can be used in displays, and Chapter 12, the final chapter of the first edition, deals with photonic devices such as beam steerers, tunable-focus lenses and polarisation-independent devices. In this second edition, four new chapters have been added two on blue phase and polymer stabilised blue phase hquid crystals, which are emerging from the realm of academic research to show promise for very fast response display and photonic devices, a chapter which discusses LCD componentry, and a final chapter on the use of LCDs in 3D display systems. 

Emoto A, Uchida E, Fukuda T (2012) Optical and physical applications of photocontrollable materials azobenzene-containing and liquid crystalline polymers. Polymers 4 150-186 Ericson LM, Fan H, Peng HQ, Davis VA, Zhou W, Sulpizio J, Wang Y, Booker R, Vavro J, Guthy C et al (2004) Macroscopic, neat, single-walled carbon nanotube fibers. Science 305 1447-1450 Etchegoin P (2000) Blue phases of cholesteric liquid crystals as thermotropic photonic crystals. Phys Rev E 62 1435-1437... 

Etchegoin, P., 2000. Blue phases of cholesteric liquid crystals as thermotropic photonic crystals. Phys. Rev. E. 62 1435-1437. 

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