Enhancing helicity-dependent optical interactions in inversion-asymmetric materials

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Nontechnical description: The human eye has evolved to perceive the intensity and color of light. However, polarization provides an additional data-rich channel for information - a property is beautifully embodied by mantis shrimp and scarab beetles, species which see circularly polarized light. Many inversion asymmetric materials - including chiral molecules and atomically-thin materials - also preferentially 'see' (that is, absorb) left- or-right circularly polarized light, but only weakly; in fact, the differential absorption of left and right circularly polarized light is nearly five orders of magnitude less than these materials' absorption of unpolarized light. This project enhances the optical absorption and emission of circularly-polarized light in molecular and monolayer materials through the design, synthesis, and characterization of new materials and nanostructures that control light-matter interactions. By increasing chiral light-matter interactions, the research increases the efficacy and reduces the unwanted side effects of pharmaceutical drugs; reduces the toxicity and environmental impact of herbicides and pesticides; and facilitates efficient quantum optoelectronic information processing. As part of the project, the Principal Investigator is engaging in outreach and mentoring with K-12 students and teachers, giving particular attention to underrepresented groups; developing new undergraduate and graduate curriculum; and implementing a national theatre production via a playwright residency.Technical description: Many inversion-asymmetric materials, including chiral molecules and certain van der Waals materials, exhibit a differential absorption of left and right circularly polarized light that is nearly five orders of magnitude less than their absorption of unpolarized light. Such weak differential absorption prohibits applications including single molecule circular dichroism spectroscopy, all-optical chiral resolution, and efficient valleytronic data encoding for quantum information. This project focuses on enhancing helicity-dependent optical absorption, emission, and carrier relaxation in molecules and monolayered materials. The approach is based on nanostructured materials known as metasurfaces, which, when placed in the near-field of a molecular or monolayer sample, precisely control the amplitude, phase, and polarization of light. Full-field electromagnetic simulations are used to design metasurfaces for strong chiral-optical absorption and emission. In parallel, high-quality factor dielectric metasurfaces are fabricated and a suite of optical and atomic force microscopies are developed to characterize how the metasurfaces enhance molecular and monolayer circular dichroism, photoluminescence, and enantioselective absorption. Finally, the metasurfaces are used to manipulate electron spin orientation and carrier dynamics in molecular and van der Waals materials with broken inversion symmetry. Conclusions drawn from the project are expected to find applicability in all-optical enantioselective sensing and separation as well as quantum optical information generation, transmission and storage.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.