THE DEVELOPMENT OF NEW POLARIZATION-MODULATION SPECTROMETER FOR SIMULTANEOUS CIRCULAR DICHROISM AND OPTICAL ROTATORY DISPERSION MESUREMENTS

从米勒矩阵方法出发，设计并构建了一种可同时测量圆二色(CD)和旋光色散(ORD)的新型偏振调制光谱仪。我们还利用Mueller矩阵分析和评估了基线漂移的可能原因和决定新光谱仪性能的其他重要特征。我们发现，我们的光谱仪的性能主要取决于以下几个因素：1.锁相放大器的谐波抑制；2.用作偏振器和分析器的双折射棱镜的质量；3.分析器的位置；4.光弹调制器的剩余静态双折射；5.用作调制器窗口的石英片的剩余静态双折射。我们用最高质量的锁定放大器、调制器、石英片和安装在专门设计的微调棱镜支架上的棱镜消除了上述障碍。因此，我们的新光谱仪测量CD和ORD信号的能力与商业上销售的200 nm到700 nm范围内的Cd和ORD偏振光谱仪相当。利用数据转换DT-2805I/O板，成功地将IBM PC/XT PC机与我们的光谱仪接口，实现了在线实时数据采集和数据处理。这些程序的所有程序都是用MacMillan软件公司的ASYST编写的。

From the Mueller matrix approach, we designed and constructed a new polarization-modulation spectrometer for simultaneous circular dichroism(CD) and optical rotatory dispersion(ORD) measurements. We also used the Mueller matrix for analyzing and evaluating the possible causes of the base-line shift and other important features determining the performance of the new spectrometer. We have found that the performance of our spectrometer depends upon mainly the following facts: 1. the harmonic rejection of the lock-in amplifiers, 2. the quality of the birefringent prisms used as the polarizer and the analyzer, 3. the position of the analyzer, 4. the residual static birefringence of the photo-elastic modulator, 5. the residual static birefringence of the quartz plates used as the windows of the modulator.We have cleared away the above obstacles by using the highest quality of the lock-in amplifiers, of the modulator, of the quartz plates, and of the prisms mounted on the prism holders specially designed for delicate adjustment. As a result, the capability of our new spectrometer in measuring CD and ORD signals is equal to that of commercially available CD and ORD spectropolarimeters in the range from 200nm to 700nm. We have also successfully interfaced an IBM PC/XT personal computer to our spectrometer by using a Data Translation DT-2805 I/O board, and accomplished on-line real-time data acqusition and data-processing. The all programs for these procedures are written in ASYST available from MacMillan Software Co..