East Carolina University, Department of Physics, Greenville, NC 27858 USA.
Appl Spectrosc. 2013 Oct;67(10):1200-4. doi: 10.1366/12-06962.
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).
几乎所有的圆二色性（CD）和线二色性（LD）光谱仪都使用电光调制器（PEM），其中光学元件通过高压信号（HT）施加应力以产生双折射。双折射随后在穿过 PEM 的光的两个垂直偏振态之间产生适当的 CD 或 LD 测量相位差。然而，即使没有外部应力（即，零 HT），PEM 也表现出固有静态双折射。本文讨论了 PEM 固有静态双折射的特性及其对 CD 和 LD 测量的影响，以及开发和实施一种新模型以适应静态双折射的存在。该模型通过使用纯手性或线性结构分子（樟脑磺酸和桑黄素）的 CD 和 LD 实验进行了验证。
