Suspensions of polystyrene latex beads in chiral solutions were investigated. The rotatory power, induced by solubilized sucrose, in near-forward scattering was measured via a method using polarization modulation by photo-elastic modulator. The sensitivity of the measurement was enhanced and optimized in order to measure sucrose concentrations as low as 5 mg/ml in a cell 5 mm thick only. Different concentrations and diameters of latex particles were used in combination with different sucrose concentrations going from 1 mg/ml up to saturation. The experiments showed that the apparent rotatory power is enhanced by multiple scattering, that depolarization effects are less important with highly concentrated sucrose solutions and that attention has to be paid to cell border effects in order to avoid important artifacts, in case of highly scattering suspensions. Qualitative and theoretical explanations of those observations are presented. One possible application of this method is to measure the sugar content in human blood, in vivo, non-invasively, through the skin. The concentration to be evaluated is at the sensitivity limit. So any artifact has to be removed carefully, e.g. skin cell birefringence or chirality.
The difference in specular reflection of left and right circularly polarized light from a naturally optically active sample (an absorbing chiral liquid) was observed and measured as a function of wavenumber under conditions of double-pass total reflection. The imaginary part of the refractive index reached a maximum value on the order of 10-4 (at 21,000 cm-1); the real and imaginary parts of the complex gyrotropic parameter were on the order of 10-8 and 5 X 10-7, respectively. In accord with recent predictions, the observed differential circular reflection exceeded the intrinsic chiral parameters by some three orders of magnitude. This is the first observation of natural molecular optical activity by coherent light scattering.
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