Optical Linear and Nonlinear

The optical properties of chiral nematic liquid crystals are unique in that, without ab- 

The first application arising as a result of Eqs. (3) and (4) is in optical filters. Here the selective transmission or reflective properties are used to select a narrow spectral band [9, 181-183], i.e., notch filters, or even a wide spectral band [184], of optical frequencies. As a result of the circular polarization properties, this also leads to the production of polarizers and retardation plates [181]. The light reflected from a planar or Grand-jean texture is either right- or left-handed cireularly polarized at normal incidence. The eombination of two such films of opposite handedness leads to notch and band pass filters capable of selecting bandwidths of a few nanometers or so, depending on Eqs. (3) and (4) from an unpolarized spectrum, i.e.. 

A different and quite remarkable application of chiral nematic wide band filters fol- 

The application of chiral nematics to THG processes has long been recognized [198-200]. These are passive applications in which mirrorless optical bistability has been predicted [198] and the theory modi- 

Biomedical thermography [222] is used extensively as a thermal mapping technique to indicate a wide range of subcutaneous medical disorders. The first use of chiral nematics to indicate skin temperature was over 30 years ago [223]. Such devices are normally constrained to indicate temperature in the 30-33°C temperature range, over which the whole color play can be exhibited. Such films have been used to indicate breast cancer [224], for placental location [225], to identify vascular disorders [226], and for skin grafting [227]. The use of chiral nematics in such areas presents an inexpensive rapid screening technique which is only indicative, since local patient and environment conditions, e.g., room and patient temperatures and internal film pressure, may lead to some false readings. This is discussed in more detail in [97]. 

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Xi f i terms are the components the nth-order electric susceptibility of the medium, is a (n- - l)-order tensor that determines completely the optical (linear and nonlinear) properties of the medium. Conservation of energy requires that... 

The polarization P is given in tenns of E by the constitutive relation of the material. For the present discussion, we assume that the polarization P r) depends only on the field E evaluated at the same position r. This is the so-called dipole approximation. In later discussions, however, we will consider, in some specific cases, the contribution of a polarization that has a non-local spatial dependence on the optical field. Once we have augmented the system of equation B 1.5.16. equation B 1.5.17. equation B 1.5.18. equation B 1.5.19 and equation B 1.5.20 with the constitutive relation for the dependence of Pon E, we may solve for the radiation fields. This relation is generally characterized tlirough the use of linear and nonlinear susceptibility tensors, the subject to which we now turn. 

The linear and nonlinear optical responses for this problem are defined by e, 2, e and respectively, as indicated in figure Bl.5.5. In order to detemiine the nonlinear radiation, we need to introduce appropriate pump radiation fields E(m ) and (co2)- If these pump beams are well-collimated, they will give rise to well-collimated radiation emitted tlirough the surface nonlmear response. Because the nonlinear response is present only in a thin layer, phase matching [37] considerations are unimportant and nonlinear emission will be present in both transmitted and reflected directions. 

Polarization which can be induced in nonconducting materials by means of an externally appHed electric field is one of the most important parameters in the theory of insulators, which are called dielectrics when their polarizabiUty is under consideration (1). Experimental investigations have shown that these materials can be divided into linear and nonlinear dielectrics in accordance with their behavior in a realizable range of the electric field. The electric polarization PI of linear dielectrics depends linearly on the electric field E, whereas that of nonlinear dielectrics is a nonlinear function of the electric field (2). The polarization values which can be measured in linear (normal) dielectrics upon appHcation of experimentally attainable electric fields are usually small. However, a certain group of nonlinear dielectrics exhibit polarization values which are several orders of magnitude larger than those observed in normal dielectrics (3). Consequentiy, a number of useful physical properties related to the polarization of the materials, such as elastic, thermal, optical, electromechanical, etc, are observed in these groups of nonlinear dielectrics (4). 

Dispersion of Linear and Nonlinear Optical Properties of Benzene An Ab Initio Time-Dependent Coupled-Perturbed Hartree-Fock Study Shashi P. Kama, Gautam B. Talapatra and Paras N. Prasad Journal of Chemical Physics 95 (1991) 5873-5881... 

Table 2. Linear and nonlinear optical properties of azobenzene dendrimers...

Experimental Methodologies for Linear and Nonlinear Optical Characterization. 116... 

The asymmetrical D-ji-A dyes, often referred to as push-pull polyenes, are an additional class of cyanine-like molecules of interest. Due to their dipolar nature, the linear and nonlinear optical properties of this series of dyes can be strongly influenced by solvent polarity [84]. The structures of a series of such dyes (G19,... 

Except through the study of linear and nonlinear optical properties of molecular crystals, methods to determine the nature of / require evaluation of appropriate characteristics of... 

The linear and nonlinear optical properties of the conjugated polymeric crystals are reviewed. It is shown that the dimensionality of the rr-electron distribution and electron-phonon interaction drastically influence the order of magnitude and time response of these properties. The one-dimensional conjugated crystals show the strongest nonlinearities their response time is determined by the diffusion time of the intrinsic conjugation defects whose dynamics are described within the soliton picture. 

By extension one may say that the power laws (5-7) which determine the magnitude of the linear and nonlinear optical coefficients are consequences of this strong electron-lattice coupling. We now make the conjecture that the time response of these coefficients is severely affected by the dynamics of the electron-lattice coupling in conjugated chains when two or more resonant chemical structures can coexist this is the case for many of the organic chains of Figure 2. 

Thus the ir-electron delocalization length Lj and the linear and nonlinear optical coefficients in ID conjugated systems reach their... 

The linear and nonlinear optical properties of one-dimensional conjugated polymers contain a wealth of information closely related to the structure and dynamics of the ir-electron distribution and to their interaction with the lattice distorsions. The existing values of the nonlinear susceptibilities indicate that these materials are strong candidates for nonlinear optical devices in different applications. However their time response may be limited by the diffusion time of intrinsic conjugation defects and the electron-phonon coupling. Since these defects arise from competition of resonant chemical structures the possible remedy is to control this competition without affecting the delocalization. The understanding of the polymerisation process is consequently essential. 

This paper will review the linear and nonlinear optical properties of polydiacetylenes with an emphasis on our work with the nBCMU polymers. The following section will discuss material... 

We first discuss the materials research which includes monomer synthesis, growth of monomer crystalline structures and polymerization in the solid state, yielding the requisite polymer structures. Next, the nonlinear optical experimental research is discussed which includes a novel experimental technique to measure x (w). Linear and nonlinear optical data obtained for the polydiacetylene films is subsequently presented. Detailed theoretical analysis relating the data to x (< >) and subsequently to its molecular basis will be discussed in a later publication. 

Linear and nonlinear optical properties of a class of polydiacetylenes that can be grown as large area and controlled thickness thin films have been investigated. This involved an integrated research effort including monomer synthesis, thin film growth and new measurement techniques. 

Conjugated polyenes exhibit large linear and nonlinear optical properties due to the mobility of electrons in extended TT-orbital systems. Hence, this is another reason for the growing interest shown in these molecules in recent years2,79-89. 

The propagation of a laser pulse focused in a plasma at high intensity is affected by several linear and nonlinear phenomena, which can modify its amplitude and therefore its possibility to travel in the medium maintaining its original interaction conditions. The main limitation arises from optical diffraction that enables the propagation at the maximum intensity only over the Rayleigh length Z i. 

In the following sections we will first in Section 2 briefly discuss the necessary background to understand optical activity effects in linear and nonlinear optics and to illustrate the similarities and differences between both types. In Section 3 we present a more thorough analysis of nonlinear optical effects in second-harmonic generation, both from a theoretical and an experimental point of view. Section 4 deals with experimental examples that illustrate the usefulness of nonlinear optical activity in the study of chiral thin films and surfaces. Finally, in Section 5 we give an overview of the role of chirality in the field of second-order nonlinear optics and show that chiral molecules can be useful for applications in this field. 

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