MRI: Track 1: Development of a Fast Multi-Contrast High-Resolution Optical Pump-Probe Microscope

Non-technical description: The goal of this project is the development of a powerful optical microscope to study the structure and function of a wide range of materials. For example, to investigate effects such as energy conversion in solar cells, the microscope needs to be able to record energy signatures on a microscopic scale, operate fast enough to resolve the rapid dynamics (typically on the order of a trillionth of a second), and be able to handle a wide range of sample temperatures. The contrast in the new microscope is based on the interactions between the sample and multiple ultrafast optical pulses, which provides sensitivity to atomic and molecular structure and dynamics. The microscope operates at low optical powers that do not destroy the sample under study, which opens the possibility of also applying it to sensitive samples such as biological tissue. The tool enables deeper understanding of the structure and functional properties of materials for improvements in the design and manufacturing methods of new materials across multiple sectors such as semiconductors, solar cells, reaction catalysts, quantum technology, and energy storage devices. The instrument is developed and located in a user facility, which not only makes it accessible by the scientific community, but also provides training opportunities for students in the areas of materials science and biomedicine. Technical description: Nonlinear optical interactions provide important information about structure and function in many complex materials. Often, functional processes (e.g., electronic and vibrational state dynamics in excited molecules, charge carrier dynamics in semiconductors, energy transport across nanoscale interfaces) occur on time scales from below picoseconds to many microseconds and longer. Pairs of ultrafast (femtosecond) laser pulses, when timed correctly, can prepare tailored excited states in these materials, and probe their time evolution back to equilibrium with high time resolution to resolve characteristic dynamics. Ideally, the fast time resolution is complemented with high spatial resolution, where small structures or heterogeneities in larger structures can be resolved, even in three dimensions. The pump probe microscope being developed can map spatial features on the scale down to 200 nanometers, investigate transport processes (such as charge diffusion and transport), and acquire hyperspectral data with unprecedented acquisition speed. The wide range of accessible contrasts and controllable operation parameters (such as laser wavelengths, pulse timing, polarization state, and sample temperature) provides a versatile and unique tool that can improve the understanding of interactions between light and engineered and quantum materials, biological tissue, or chemical compounds at the microscopic scale. Design, construction, testing, and commissioning are performed in a core facility for general user access. 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.