MRI: Development of Ultrafast Near-Field Scanning Optical Microscope

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Many phenomena in natural and engineered systems are both spatial and temporal, meaning that they involve dynamical changes and movements of nonuniform patterns. Examples include wave propagation, heating and cooling, chemical reactions, and diffusion. The ability to visualize these phenomena is fundamentally limited both by how fast they are and how small they are. Science has made remarkable improvements in the spatial resolution of microscopes, which has enabled the now-mature field of nanotechnology. At the same time, pulsed laser systems can resolve dynamical processes with femtosecond resolution -- far faster than even the best electrical detectors or cameras. This project aims to develop a novel instrument that will combine the spatial capabilities of a near-field microscope with the temporal resolution of a femtosecond laser, which is currently not available in commercial instruments. This tool will be capable of resolving nanoscale spatial structure, while simultaneously measuring ultrafast effects with femtosecond resolution in systems ranging from nanoelectronic devices to metallic nanostructures and solar cells. The unique instrument will provide valuable training for scientists and students at all levels, who will both develop and utilize it.The combination of two different technologies, the femtosecond laser and the near-field microscope, will require significant engineering research, iteration, optimization, and system integration over the three-year period of this project. The proposed instrument will replace the continuous-wave laser typically used in a near-field scanning optical microscope with an ultrafast tunable pulsed laser, in order to produce an intense spatially and temporally localized optical stimulus that can excite nonlinear effects in the material or device at the nanoscale. A second, weaker temporally-delayed optical pulse will then be used to probe the properties and dynamics with femtosecond resolution. The proposed system will allow for time-resolved and spatially-resolved measurements at wavelengths ranging from 340 nm to 12,000 nm. The new instrument will enable the study of hot-carrier dynamics in metals and two-dimensional (2D) materials, investigation of the dynamic electrical response of perovskite materials for advanced optoelectronics, direct imaging of nanophotonic devices and resonant structures, and observation of heterogeneous surface chemistry and grain boundaries in transition-metal oxides.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.