Critical Aspects of Measurement of Circular and Linear Dichroism: A Device for Absolute Calibration

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Abstract
The polarization effect of one or several tilted, parallel air-spaced fused silica plates is calculated. It is generally necessary to include higher order reflections. A device consisting of 1–4 plates tilted 10–45° from normal incidence is proposed for the calibration of differential linear dichroism (LD) in the measurement ranges 10−3 to 10−1 decadic absorbance units and the wavelength region 200–700 nm. The experimental LD measured in these ranges on commercial circular dichrometers, converted to LD mode according to Norden and Davidsson, was in excellent agreement with the calculated, nonempirical results. Since the response function of the instrument in this conversion mode is the same for LD and CD, the method also provides a means for absolute calibration of CD. The results can also be applied to polarized scattering and fluorescence. (For previous papers on this theme, see Refs. 6, 9 and 12.)