Optical properties, of liquid crystals

Blinov L M 1983 Electro-optical and Magneto-optical Properties of Liquid Crystals (Chichester Wiley)... 

Simoni F 1997 Nonlinear Optical Properties of Liquid Crystals and Polymer-Dispersed Liquid Crystals (Singapore World Scientific)... 

The unusual optical properties of liquid crystals had been remarked upon and described for several centuries before their uniqueness as a state of matter was recognised. Their early reports described the strange melting behaviour and appearance of some naturally occurring materials, either as pure compounds or as gels in water, which have now been shown to be thermotropic or lyotropic liquid crystals. Thermotropic liquid crystalline phases are formed under the action of heat, see Figures 2.1 and 2.2, and the lyotropic liquid crystalline phases are formed by the action of a solvent, such as water, usually with an amphiphilic compound. However, the nature of these materials, or indeed their exact... 

Before these results were published, polymer physicists and chemists mainly investigated only two phase-states, amorphous and crystalline. At the present time, along with these two states, the third phase-state of condensed systems, i.e. the liquid crystalline state, became very important. Here the situation turned out to be the same as in the case of low molar mass liquid crystals. In spite of the fact that historically the low molar mass substances in liquid crystalline state had been known for about a century, the intensive study of their properties began only after they had found an important practical application owing to a sharp change in optical properties of liquid crystals in electromagnetic fields (for visual displays) and as sensitive temperature indicators (in medicine). 

In orthoscopic observations parallel rays are required because the optical property of liquid crystals is direction-dependent. Often a low-power, low aperture objective lens is used so that most of the light will travel through the sample in the same direction or nearly so. Otherwise the substage iris (D in Figure 4.4) is closed accordingly so that a sufficient approximation of the parallel condition is achieved. 

A wealth of information about photolumescent materials, their properties and conditions for their optimum preparation is found in [257]. In combination with glass substrates coated with transparent electrodes, the electro-optical properties of liquid crystal films, which themselves emit no light, offer some interesting possibilities [258, 259]. Liquid crystals have the mobility of liquids and the optical properties of solids. The molecular structure lies between the liquid and solid state. Liquid crystals are organic compounds of relatively long molecules compared with their diameter, and often contain polar groups and multiple bonds. 

Display devices can also be constructed using the field effect, the cholesteric memory effect and the cholesteric-nematic phase change effect [259, 262]. The recognition of the useful electro-optical properties of liquid crystals has stimulated efforts in synthesis of new mesomorphic materials. Today, more than 6000 compounds are available but an ideal liquid crystal is still elusive. 

F. Simoni, Nonlinear optical properties of liquid crystals and polymer dispersed liquid crystals World Scientific, Singapore 1997. 

Blinov, L.M. Electro-Optical and Magneto-Optical Properties of Liquid Crystals. Wiley, Chichester (1983) Blinov, L.M., Chigrinov, V.G. Electrooptic Effects in Liquid Crystal Materials. Springer-Verlag, New York (1993)... 

Blinov, L.M. Electro-Optical and Magneto-Optical Properties of Liquid Crystals. Wiley, Chichester (1983)... 

In 1963, Richard Williams observed the formation of very regular patterns or domains in a nematic liquid crystal when the material was subjected to an electric field. This report marked the beginning of a new era in research on the electro-optic properties of liquid crystals, a field which had laid dormant for nearly 30 years. During the remaining years of the 1960 s and the early 70 s, numerous studies of electro-optic effects in liquid crystals were performed, and at the same time, investigations into the synthetic and physical chemistry of these materials were conducted. As a result of these efforts, a whole new display industry evolved. 

For many liquid crystal devices, their optical properties cannot be calculated analytically because their refractive indices vary in space. In this chapter we will discuss methods which can be used to numerically calculate the optical properties of liquid crystal devices. 

Besides aligning liquid crystals, external electric fields can also change the orientational order and thus the electro-optical properties of liquid crystals. When the long molecular axis of a liquid crystal molecule, whose anisotropy of polarizability is positive, is parallel to the applied field, the potential of the molecule is low. Thus the applied field suppresses the thermal flue-mation and increases the order parameter. Now we discuss how the orientational order of a nematic liquid crystal changes with applied fields. Using the Landau-de Gennes theory, the free energy density of a liquid crystal in an electric field (when the liquid erystal director is parallel to the field) is [4]... 

Polymer networks formed in liquid crystals are anisotropic and affect the orientation of liquid crystals. They tend to align the liquid crystal in the direction of the fibrils. They are used to stabilize desired liquid crystal configurations and to control the electro-optical properties of liquid crystal devices. Polymer networks have been used to improve the performance, such as drive voltage and response times, of conventional liquid crystal devices such as TN and IPS displays. 

M. Ye and S. Sato, Optical properties of liquid crystal lens of any size, Jpn. J.Appl. Phys. 41, L571 (2002). 

Liquid crystal devices are the energy efficient, low-cost displays used in a variety of applications in which information or images are presented. The operation of the devices is based on the unique electrical and optical properties of liquid crystal materials. 

Laser-induced molecular reorientation is a common cause of optical nonlinearity in a fluid medium. In this respect, liquid crystals are often strongly nonlinear because of their large molecular anisotropy and strong correlation between molecules. The nonlinear optical properties of liquid crystals in the isotropic phase have already been studied quite extensively by a number of researchers in the past decade, This is, however, not true for liquid crystals in the mesophases. 

Linear and nonlinear optical properties of liquid crystals in their mesophases have been studied in several contexts, in both fundamental and application-oriented pursuits. In the context of nonlinear optical processes, they have recently received considerable renewed interests as a result of the newly discovered extraordinarily large optical nonlinearity due to the laser-induced molecular reorientation, and a renewed effort explicitly at the large thermal index effect in liquid crystals. In the last few years, several groups [2]-[10] have looked at the optical nonlinearity in the mesophases of liquid crystals and the associated nonlinear processes. A brief review of some of these nonlinear optical processes and the fundamental mechanisms in both the liquid crystal and the isotropic phases has recently appeared [1]. In this paper, therefore, we will concentrate only on optical wave mixing processes that are relevant to this Special Issue. 

A.L. Aero and M.G. Tomilin, Illrd Symposium Optical Properties of Liquid Crystals and Their Application, Leningrad, 1984, Proceedings, p. 98 (in Russian). 

Rev. ed. of Electro-optical and magneto-optical properties of liquid crystals, cl983. 

II. Blinov, L. M. (Lev Mikhailovich). Electro-optical and magneto--optical properties of liquid crystals. HI. Title. IV. Series. 

This book was conceived as a renewed version of the earlier published original book, Electro-Optical and Magneto-Optical Properties of Liquid Crystals (Wiley, Chichester, 1983) written by one of us (L.M. Blinov). That book was first published in Russian (Nauka, Moscow, 1978) and then was modified slightly for the English translation. Since then new information on electrooptical effects in liquid crystals has been published. Novel effects have been discovered in nematics and cholesterics (such as the supertwist effect), and new classes of liquid crystalline materials, such as ferroelectric liquid crystals, appear. Recently, polymer liquid crystals attracted much attention and new electrooptical effects, both in pure polymer mesophases and polymer dispersed liquid crystals, were studied. An important contribution was also made in the understanding of surface properties and related phenomena (surface anchoring and bistability, flexoelectricity, etc.). 

Polymer dispersed liquid crystals (PDLCs) are a relatively new class of composite materials consisting of micrometric liquid crystalline droplets dispersed into a polymer matrix (Bronnikov et al. 2013). Thus, they combine the unique optical properties of liquid crystals (LCs) with the film-forming ability and mechanical properties of a polymer matrix—resulting in appropriate materials for a large variety of fiexible opto-electronic applications (Bouteiller et al. 1996 Bronnikov et al. 2013 Dierking 2000 Drzaic 2006 Kitzerow 1994 Smith 1993). As evidenced by... 

Combining outstanding mechanical properties of the polymer film (high mechanical strength and flexibility) with interesting optical properties of liquid crystal (high optical anisotropy), the PDLC systems allow their use in various applications as flexible display systems, privacy or smart glass, projection devices, sensors, etc.). 

F. Simoni, Non-linear optical properties of liquid crystals and polymers dispersed liquid crystals - series on liquid crystals, Vol. 2, pp. 217-250, World Scientific, Singapore. (1997). 

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