Polariton-Assisted Imaging of Ultrafast Chemical Transformations

With support from the Chemical Measurement and Imaging (CMI) Program in the Division of Chemistry, Milan Delor and his research group at Columbia University are developing a new microscope to directly image interactions between molecules separated by large distances. These long-range molecular interactions are of high current interest for potentially transformational technologies including ultra-efficient energy harvesting, catalytic systems that drive highly complex chemical reactions, and quantum sensors that can detect the tiniest perturbations in their environment. Long-range molecular interactions are notoriously difficult to characterize and control because they occur between just a few molecules and often on extremely fast timescales, inaccessible to current technologies. The Delor group is working to develop a microscope that leverages polaritons, part-light part-matter particles, to significantly increase the sensitivity of optical microscopy and enhance long-range molecular interactions. This technology will be combined with short laser pulses and angle-resolved imaging to yield an ultrafast microscope that is designed to directly image interactions between individual molecules occurring over a trillionth of a second. The research focuses on understanding how long-range communication between molecules can be controlled. The group plans to publish extensive technical blueprints to allow other researchers to reproduce and adapt the microscope for other applications. Developing the home-built microscope and applying it to molecular systems of high current interest will also provide hands-on training for undergraduate and graduate students in optics, sensing, and chemical dynamics, areas of expertise that are in high demand in academia, government laboratories, and industry.Long-range molecular interactions induce collective dynamics that are crucial for processes as diverse as coherent energy flow, cooperative catalysis, biological allostery, and quantum entanglement. Collective effects are notoriously difficult to characterize as they typically occur on femto-microsecond timescales, in sub-ensembles of 2–100 coupled molecules, and over sub-micron spatial scales. In this project, the Delor group is working to develop a unique ultrafast imaging approach that leverages polaritons (propagating part-light, part-matter particles at metal-dielectric interfaces or in photonic cavities), combined with ultrasensitive momentum-resolved optical microscopy, to image collective effects in tiny molecular ensembles over sub-micron scales. This new approach called PolImUR (Polariton-assisted Imaging of Ultrafast photoinduced Reactions) is being implemented in a pump-probe far-field microscope that uses elastic scattering as contrast mechanism and will be optimized to leverage the extreme sensitivity of polaritons to their environment. Using a variety of polaritonic substrates, the group plans to demonstrate sub-10-molecule sensitivity and a spatiotemporal dynamic range spanning 40 femtoseconds–1 microsecond and 50 nanometers–20 microns. The researchers aims to leverage these features to directly image and characterize cooperative catalysis on plasmonic substrates, and coherent energy and information exchange between (entangled) molecules. These processes underlie efforts around the community to develop collective chemistry (e.g. polariton chemistry) and quantum technologies (e.g. remote quantum sensing) that rely on long-range molecular interactions.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.