Abstract
A macroscopic theory is developed to explain the intense and highly structured circular dichroism (CD) and optical rotary dispersion (ORD) measurements of cholesteric liquid crystals in spectral regions of absorption, e.g., in the infrared. Oseen’s helical model of the dielectric tensor of the liquid crystal is used. The effects of each absorption band are represented by frequency-dependent, complex terms in the dielectric tensor. Assuming reasonable values for the absorptive parameters of the band, we are able to explain the magnitude and shape of the CD and ORD spectra, as well as their trends with the pitch of the helix. The calculated sign of the Cotton effect is shown to depend upon the direction of polarization of the absorption band with respect to the background birefringence. The observed preponderance of bands with one sign is qualitatively explained on the basis of the molecular structure of the liquid crystal.
© 1973 Optical Society of America
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