Department of Physics, Howell Science Complex, East Carolina University, Greenville, NC 27858, USA.
Appl Spectrosc. 2013 Jan;67(1):40-8. doi: 10.1366/12-06649.
Both the voltage-induced and the inherent (static) birefringence of a photoelastic modulator (PEM) affect the phase difference between orthogonal components of light passing through the PEM. This phase difference determines the polarization state of the light and is essential for determining true circular and linear dichroism (CD and LD, respectively) spectroscopy. Presented here are a more complete theoretical model of CD and LD and a new technique to determine the phase difference and static birefringence of a PEM in CD and LD. The intensity of the light for various configurations of the analyzer is interpreted (by using Mueller matrices and Stokes parameters) to calibrate the voltage-induced phase difference and to characterize the static birefringence in the photoelastic modulator. The effects of the static birefringence as well as intermediate polarization states (between left- and right-circularly polarized light) on LD and CD are characterized. Appropriate adjustments to the voltage applied to the PEM in order to mitigate these effects are discussed. It is expected that the techniques presented here will have a broad impact on the calibration of CD and LD spectrometers.
光弹调制器（PEM）的电压诱导双折射和固有（静态）双折射都会影响通过 PEM 的正交分量光之间的相位差。该相位差决定了光的偏振状态，对于确定真正的圆二色性（CD）和线二色性（LD）光谱至关重要。本文提出了一种更完整的 CD 和 LD 的理论模型，以及一种新的技术，用于确定 CD 和 LD 中 PEM 的相位差和静态双折射。通过使用 Mueller 矩阵和 Stokes 参数解释了各种分光镜配置下光的强度，以校准电压诱导的相位差，并表征光弹调制器中的静态双折射。还对静态双折射以及中间偏振态（介于左旋圆偏振光和右旋圆偏振光之间）对 LD 和 CD 的影响进行了表征。讨论了为减轻这些影响而对 PEM 施加的电压进行适当调整的问题。预计这里提出的技术将对 CD 和 LD 光谱仪的校准产生广泛影响。
