• Korean Journal of Optics and Photonics
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• v.27 no.6
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• pp.223-228
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• 2016

The birefringence of distributed, uniaxially anisotropic molecules like liquid crystals is calculated as the degree of ordering is varied. The relation between the normalized birefringence ${\Delta}n_{rel}$ and the orientational order parameter S is investigated. The distribution function, which enables one to monitor the degree of ordering of liquid crystals including randomly distributed ones, is introduced. Using this distribution function, a series of distributed liquid crystals with order parameters ranging from 0 to 1 are generated, and ${\Delta}n_{rel}$ and S of the correspondingly distributed liquid crystals are calculated. Based on the calculated data, it is revealed that ${\Delta}n_{rel}$ and S satisfy the quasi-linear relation of $S=(1+a){\Delta}n_{rel}-a{\Delta}n^2_{rel}$, where a can be approximated as $n_o{\frac{{\Delta}n}{4}}$. The anisotropy of molecular polarizability is also calculated, using the birefringence, and separately following Vuks' method and Neugebauer's method, and it is shown that the relations between S and the molecular-polarizability anisotropy are also quasi-linear.

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1126-1134
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• 2003

The signals obtained from the $5^{th}$-order (two-dimensional) Raman spectrum of a liquid can depend dramatically on the polarizations of the various light beams, but to date there has been no evidence presented that different polarization conditions probe any fundamentally different aspects of liquid dynamics. In order to explore the molecular significance of polarization we have carried out a molecular dynamics simulation of the $5^{th}$-order spectrum of a dilute solution of CS₂ in liquid Xe, perhaps the simplest system capable of displaying a full range of polarization dependencies. By focusing on the 5 distinct rotational invariants revealed by the different polarizations and by comparing our results with those from liquid Xe, a liquid whose spectrum has no significant polarization dependence, we discovered that the polarization experiments do, in fact, yield valuable microscopic information. With different linear combinations of the experimental response functions one can separate the part of the signal derived from the purely interaction-induced part of the many-body polarizability from the portion with the largest contributions from single-molecule polarizabilities. This division does not directly address the underlying liquid dynamics, but it significantly simplifies the interpretation of the theoretical calculations which do address this issue. We find that the different linear combinations differ as well in whether they exhibit nodal lines. Despite the absence of nodes with the atomic liquid Xe, observing the resilience of our solution's nodes when we artificially remove the anisotropy of our solute leads us to conclude that there is no direct connection between nodes and specifically molecular degrees of freedom.