Polariton-Assisted Imaging of Ultrafast Chemical Transformations

在化学系化学测量与成像（CMI）项目的支持下，哥伦比亚大学的Milan Delor和他的研究小组正在开发一种新型显微镜，可以直接成像相隔很远的分子之间的相互作用。这些远程分子相互作用是目前潜在的转型技术的高度兴趣，包括超高效能量收集，驱动高度复杂化学反应的催化系统，以及可以检测环境中最微小扰动的量子传感器。众所周知，远程分子相互作用很难表征和控制，因为它们只发生在几个分子之间，而且通常发生在极快的时间尺度上，这是目前技术无法实现的。Delor团队正致力于开发一种显微镜，利用偏振子，部分光部分物质粒子，来显著提高光学显微镜的灵敏度，增强远程分子相互作用。这项技术将与短激光脉冲和角度分辨成像相结合，产生一种超快显微镜，可以直接成像单个分子之间在万亿分之一秒内发生的相互作用。这项研究的重点是了解如何控制分子之间的远距离通信。该小组计划发布广泛的技术蓝图，以允许其他研究人员复制和调整显微镜用于其他应用。开发自制显微镜并将其应用于当前高度关注的分子系统，还将为光学、传感和化学动力学领域的本科生和研究生提供实践培训，这些领域的专业知识在学术界、政府实验室和工业界都有很高的需求。远程分子相互作用诱导集体动力学，这对于相干能量流、协同催化、生物变构和量子纠缠等多种过程至关重要。众所周知，集体效应很难表征，因为它们通常发生在飞微秒时间尺度上，在2-100个耦合分子的子集合中，以及在亚微米空间尺度上。在这个项目中，Delor团队正在开发一种独特的超快成像方法，利用极化子（在金属-介电界面或光子腔中传播部分光、部分物质粒子），结合超灵敏的动量分辨光学显微镜，在亚微米尺度上对微小分子集合体的集体效应进行成像。这种被称为PolImUR（超快光诱导反应的极化辅助成像）的新方法正在泵浦探针远场显微镜中实现，该显微镜使用弹性散射作为对比机制，并将优化以利用极化对其环境的极端敏感性。利用多种极化基底，该小组计划展示亚10分子的灵敏度和跨越40飞秒（1微秒）和50纳米（20微米）的时空动态范围。研究人员的目标是利用这些特征直接成像和表征等离子体底物上的协同催化作用，以及（纠缠）分子之间的相干能量和信息交换。这些过程是社区发展集体化学（如极化化学）和量子技术（如远程量子传感）的基础，这些技术依赖于远程分子相互作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.