ANALYSIS OF OPTICAL ARTIFACTS IN ELLIPSOMETRIC MEASUREMENTS OF TIME-RESOLVED CIRCULAR-DICHROISM

Time-resolved circular dichroism (TRCD) measurements of dynamic molecular processes initiated by a linearly polarized laser pulse may be distorted by photoselectively induced linear artifacts (PSLA), such as linear birefringence (LB) and linear dichroism (LD), if measurement times are not much longer than the molecular reorientation times of the absorbing species. In principle, the ciruclar birefringence (CB) that accompanies CD can also affect ellipsometric measurements. Additionally, imperfect optics such as strained sample cell windows and misaligned polarizers can introduce error in the detection of the CD signal. A Jones matrix analysis of the TRCD optical system is presented that considers all of these effects and the important couplings between them. Qualitative as well as quantitative analyses of the effects are discussed. The effect of CB on TRCD measurements is shown to be negligible for physically relevant systems, i.e. those that follow the Kramers-Kroning relation. Experimental strategies for minimizing the effects of PSLA and optical imperfections on TRCD measurements are described. Experimental results are presented that corroborate the theoretical analysis and demonstrate the efficacy of the strategies presented.