E. H. Korte

Total Reflection Prisms as Achromatic IR Retarders

Retarders based on total internal reflections are discussed. Quarterwave retardation can be obtained by a single reflection when one is using material of high refractive index (≥2.4), as it is available for the IR range. Alternatively, the influence of the beam divergence can be efficiently compensated for. Several optical designs and first results are presented.

Efficiency in Circular Polarization Modulation

The efficiency of a retarder for conversion of linear polarization into circular polarization is defined. The average efficiency is calculated for the cases in which either the polarization plane of incident radiation or the phase retardation is modulated. Three different modulation functions are considered.

Measurement of the IR-ORD of Induced Cholesteric Solutions in Presence of Linear Dichroism

The sign of absorption-induced Cotton effects in the IR-ORD spectra of induced cholesteric solutions allows us to distinguish between enantiometric solutes. It is shown here that the often distorted shape of these rotatory anomalies, sometimes making the evaluation ambiguous (in particular for highly diluted solutions), is due to the superimposition of a linear dichroism band and that this can be compensated for by appropriate orientation of the sample. In this way the necessary quantity of optically active solute can be lowered considerably.

Sampling depth in infrared diffuse reflection spectroscopy of undiluted samples

Diffuse reflectance of strongly absorbing sample layers is calculated in dependence of their thicknesses from the Kubelka-Munk theory. The results are compared to experimental ones from varnish layers on reflecting metal substrates.

FTIR measurements of optical rotatory dispersion and circular dichroism

FTIR methods for measuring optical rotatory dispersion (ORD) and circular dichroism (CD) were developed. The measurements of both phenomena are accomplished by means of various techniques. The study of ORD makes use of linearly polarized IR radiation while that of CD requires a circular polarizer (retarder) able to convert linearly polarized IR radiation into circularly polarized one. Examples of induced cholesteric solutions are shown.