Procedures for attenuated total reflection study of extremely small samples.
The conditions controlling the sensitivity of ATR toward extremely small samples are discussed with a view to their optimization. It is found that the formulas developed by Harrick and du Pré for thin film ATR apply to this case, with certain modifications. Optimum values for the indices of the optical material, sample, and backing, as well as for the incidence angle, are given for light of both polarizations. The advantages of reflecting the light beam several times on the same sample spot are pointed out, and three optical systems are proposed for this. These are a flat trapezoidal ATR plate with slant illumination, a cylinder with side-on illumination at an oblique angle to the axis, and a hemisphere ridged with retroreflecting teeth, wherein the beam repeatedly strikes the center with a rotating incidence plane. Modifications of the latter cell are proposed to make its use more convenient, as well as adaptations of its principle for conventional reflection, transmission, and ATR fluorescence work.
Hirschfeld
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North American Aviation Science Center, Thousand Oaks, California 91360, USA.