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Modeling, Characterizing, and Accommodating Static Birefringence in Circular and Linear Dichroism Spectroscopy
Volume 67, Number 10 (Oct. 2013) Page 1200-1204
JULIE M. DINITTO and JOHN M. KENNEY*
Nearly all circular dichroism (CD) and linear dichroism (LD) spectrometers use a photoelastic modulator (PEM) in which an optical element is stressed using a high-tension voltage (HT) signal to induce birefringence. The birefringence consequently produces a phase difference between perpendicular polarization states of light passing through the PEM that is appropriate to CD or LD measurements. However, even without external stress (i.e., at zero HT) the PEM exhibits an inherent static birefringence. This article discusses the characterization of the static birefringence inherent to a PEM and its effect on the measurement of CD and LD, as well as the development and implementation of a novel model that accommodates for the presence of static birefringence. The model is validated with CD and LD experiments using purely chiral or linearly structured molecules (camphorsulfonic acid and chrysazin).
Index Headings: Circular dichroism; Linear dichroism; Camphorsulfonic Acid; Chrysazin; Photoelastic modulator; Static birefringence.