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Physical Chemistry Seminar: Professor Keith Nelson, MIT

Keith Nelson
Date
Tue November 19th 2024, 3:00 - 4:00pm
Location
Sapp Center Lecture Hall 114

About the Seminar

Light over matter: Controlling and measuring molecules and materials

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 RF-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. Two additional new capabilities for reaching important nonequilibrium configurations will be summarized briefly. Optically generated strain waves are 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. Finally, ultrashort x-ray pulses can be used for excitation as well as probing, and because of their short wavelength they provide direct access to nanoscale spatial modulations and corresponding high-wavevector coherent material modes.

About the Speaker 

Keith Nelson joined the faculty of the MIT Department of Chemistry in 1982 after completing his graduate study at Stanford University in 1981 and postdoctoral research 1981-1982 at UCLA. His research involves development and use of modern methods in ultrafast time-resolved spectroscopy of molecules and materials in THz, IR, optical, EUV, and x-ray spectral ranges. It includes study of far-from-equilibrium states of matter induced by electromagnetic and mechanical stimuli on time scales ranging from femtoseconds to milliseconds.

Host: Fang Liu