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

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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..