Principles of Circular Dichroism Detection Using Vector Vortex Beam and Orbital Angular Momentum Sorting

초록

We present a theoretical and conceptual framework for single-shot detection of electronic or vibrational circular dichroism (CD) using vector vortex beams combined with orbital angular momentum (OAM) sorting. In this approach, a linearly polarized Gaussian beam is transformed by a q-plate into a spin-orbit superposition comprising left- and right-circularly polarized components carrying equal and opposite OAM. When this structured beam interacts with a chiral sample, the two spin components experience unequal attenuation, producing an intrinsic intensity imbalance directly proportional to the sample's CD. An OAM sorter then spatially separates these components, enabling their intensity ratio to be measured in a single exposure without polarization modulation or sequential acquisition. Analytical derivations show that the differential absorbance can be extracted from the logarithmic ratio of the two OAM-channel intensities. We further discuss experimental requirements, calibration strategies, and potential for lock-in detection schemes for achieving shot-noise-limited sensitivity. This method unifies structured-light photonics and chiroptical spectroscopy, offering a robust, calibration-friendly, and geometrically intuitive pathway for high-speed, high-precision CD measurements using spatially multiplexed structured beams.

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