Hutchison Hall, Rochester, NY

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Join us to hear from MIT's Keith A Nelson about his research!

Abstract: Parallel developments in optics and spectroscopy have brought us to a new era of optical control and measurement. We have light pulses, pulse sequences and waveforms with strong fields and high intensities, controlled temporal and polarization profiles, and specified spatial distributions spanning microwave-THz-IR-visible-UV-x-ray spectral ranges. These allow us to drive molecules and materials away from their equilibrium configurations with extraordinary control and to monitor their dynamical responses in incisive ways. We will emphasize the THz spectral range and show how strong THz fields have been used to reveal new intermolecular interactions, to conduct electron paramagnetic resonance spectroscopy of high-spin molecular compounds and collective magnetic modes, to induce charge transfer, and to drive electronic and structural phase transitions. Dynamical probes include 2D THz spectroscopic measurements, visible light polarization and harmonic generation measurements, ultrafast x-ray diffraction and diffuse scattering, and single-shot real-time measurements of far-from-equilibrium evolution when needed to observe an irreversible process that permanently alters a solid sample. Further control over excursions away from equilibrium through optically generated strain waves is opening the door to tabletop ultrahigh-pressure science and to multimodal excitation of lattice, electronic, and spin degrees of freedom whose coupled responses traverse free-energy landscapes of complex materials with multiple structurally, electronically, and magnetically ordered phases.

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