Transient Electro-Optic Kerr Effect in Liquid Crystalline Isothiocyanates
15 Jun 1999-Journal of the Physical Society of Japan (Physical Society of Japan)-Vol. 68, Iss: 6, pp 1939-1942
TL;DR: In this paper, the D.C. Kerr response and the pre-transitional behavior of two liquid crystalline isothiocyanates 4-(4 ′ -n-pentyl phenyl)-phenyl isothIocyanate (5NCS) and 4-( 4 ′ −n-heptylphenyl-phenyl)-isothIOCyanate(7NCS), at temperatures above the smectic-isotropic transition temperatures were investigated.
Abstract: Measurements are reported for the first time on the D.C. Kerr response and the pre-transitional behaviour of two liquid crystalline isothiocyanates 4-(4 ′ -n-pentyl phenyl)-phenyl isothiocyanate (5NCS) and 4-(4 ′ -n-heptyl phenyl)-phenyl isothiocyanate (7NCS) at temperatures above the smectic-isotropic transition temperatures. The Kerr law has been verified and the real part of the third order nonlinear susceptibilities (χ (3) ) above the smectic-isotropic transition are determined for the two liquid crystalline isothiocyanates from the electro-optic Kerr effect (EOKE) experiments. The variation of susceptibility with temperature has also been studied. The results have been compared with the cyanobiphenyls which have been widely studied and are known for their giant optical non-linearities.
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TL;DR: In this article, a phenomenological model is developed to describe the effect of nonmesogenic impurities on the isotropic to smectic-A phase transition, based on the coupling of the power expansions associated with the concentration variable and the symmetry-breaking order parameters.
Abstract: A phenomenological model is developed to describe the effect of nonmesogenic impurities on the isotropic to smectic-A phase transition. It is based on the coupling of the power expansions associated with the concentration variable and the symmetry-breaking order parameters. While this phase transition is first order in the mesogenic pure compound consisting of smectic-A phase, we show here that the order of this transition does not change when the nonmesogenic solute is added to a mesogenic pure compound. It is shown that the isotropic to smectic-A phase transition temperature is depressed and a two-phase region is formed due to the presence of impurities of the solutes. The available experimental data are consistent with our model.
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TL;DR: The physical mechanisms which can produce second-order dielectric polarization are discussed on the basis of a simple extension of the theory of dispersion in ionic crystals in this paper.
Abstract: The physical mechanisms which can produce second-order dielectric polarization are discussed on the basis of a simple extension of the theory of dispersion in ionic crystals. Four distinct mechanisms are described, three of which are related to the anharmonicity, second-order moment, and Raman scattering of the lattice. These mechanisms are strongly frequency dependent, since they involve ionic motions with resonant frequencies lower than the light frequency. The other mechanism is related to electronic processes of higher frequency than the light, and, therefore, is essentially flat in the range of the frequencies of optical masers. Since this range lies an order of magnitude higher than the ionic resonances, the fourth mechanism may be the dominant one. On the other hand, a consideration of the linear electro-optic effect shows that the lattice is strongly involved in this effect, and, therefore, may be very much less linear than the electrons. It is shown that the question of the mechanism involved in the second harmonic generation of light from strong laser beams may be settled by experiments which test the symmetry of the effect. The electronic mechanism is subject to further symmetry requirements beyond those for piezoelectric coefficients. In many cases, this would greatly reduce the number of independent constants describing the effect. In particular, for quartz and KDP there would be a single constant.
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TL;DR: A detailed survey of the present-day knowledge of optical compensators is given in this article, with a reference made to the sensitivity and accuracy of the compensators and their applications.
Abstract: A detailed survey is given of the present-day knowledge of optical compensators. The compensators discussed are those of Babinet, Soleil, Rayleigh, De Forest Palmer, Brace, Szivessy, Senarmont, and Richartz. Each instrument is described, the theory developed, the method of use for the measurement of small phase differences given, and reference made to the sensitivity and accuracy.
157 citations
TL;DR: In this paper, the authors measured the optical Kerr effect and the intensity-dependent ellipse rotation in order to study the pretransitional behavior of field-induced molecular alignment in the isotropic nematic substances.
Abstract: We have measured the optical Kerr effect and the intensity-dependent ellipse rotation in order to study the pretransitional behavior of field-induced molecular alignment in the isotropic nematic substances $p$-methoxy-benzylidene $p\ensuremath{-}n$-butylaniline (MBBA) and $p$-ethoxy-benzylidene-$p$-butylaniline (EBBA). The results agree well with predictions of the Landau---de Gennes model. Both the order-parameter relaxation time and the steady-state field-induced birefringence show critical divergence towards the isotropic \ensuremath{\rightarrow} nematic transition with a ${(T\ensuremath{-}{T}^{*})}^{\ensuremath{-}1}$ temperature dependence. In the case of MBBA, our results are also consistent with the results from light scattering, but the method we use is perhaps more straightforward and accurate. The nonlinear refractive indices and other relevant parameters of the materials are derived from the experiment.
135 citations
101 citations
TL;DR: In this paper, the authors studied the pretransitional behavior of a series of mesomorphic compounds, the alkyl cyanobiphenyls (CNρρC n H 2n + 1) for n = 5-12, and showed that the presence of the smectic A phase changes markedly the pret-ransitional behaviour, and gives rise to two distinct pret-transitional regions.
Abstract: The pretransitional behaviour of a homologous series of mesomorphic compounds, the alkyl cyanobiphenyls (CNρρC n H 2n + 1) for n = 5–12, has been studied as a function of temperature by light scattering in the isotropic phase. The higher homologues, n = 8–12, exhibit a smectic A phase that becomes increasingly important at the expense of the nematic phase for increasing n and for n = 10 and 12 no nematic phase is observed. We have shown from light scattering and differential scanning calorimetry measurements that the presence of the smectic A phase changes markedly the pretransitional behaviour, and gives rise to two distinct pretransitional regions. The first region is for temperatures greater than ∼3°C above the clearing temperature Tc where the systems exhibit a typical pretransitional behaviour adequately described by the phenomenological Landau-de Gennes model of a second order phase transition with an intervering first order transition at Tc . The constants of this model for this region are...
66 citations