Circular dichroism (CD) spectroscopy of gaseous molecules remains challenging because of intrinsically weak CD signals and low molecular number densities, which necessitate the use of pulsed molecular beams and high-power pulsed lasers. Pulse-to-pulse intensity fluctuations in both systems introduce variations in ionsignals, leading to fluctuation-induced artifacts in the measured CD values. To suppress these effects, we developed a CD measurement technique that employs randomly alternating left- and right-handed circularly polarized laser pulses (random-CP). Unlike conventional regularly alternating circularly polarized pulses (regular-CP), random-CP pulses decouple periodic experimental fluctuations from the CD signal, thereby minimizing systematic artifacts and improving precision. The advantages of this approach are demonstrated through resonant two-photon ionization CD and fluorescence-detected CD spectra of jet-cooled (R)-(+)-styrene oxide recorded near the origin band of the S0 – S1 transition. Compared with regular-CP pulses, random-CP pulses lead to more rapid convergence of CD values, more consistent CD band profiles, and effective suppression of offset biases. This random-CP pulse strategy provides a robust and broadly applicable method for enhancing the accuracy and reliability of gas-phase CD measurements.
Yun et al. (2026) studied this question.