Optical spectroscopy and optical control of collective degrees of freedom in many material classes

Keith Nelson
Massachusetts Institute of Technology
Carnegie 113, Rensselaer Polytechnic Institute
Fri, April 05, 2024 at 2:00 PM

Advances in optics and in the harnessing of light-matter interactions have led to corresponding advances in coherent optical excitation and monitoring of collective degrees of freedom including transverse and longitudinal acoustic modes, optical phonons, and magnons both within and far beyond their linear-response regimes. Acoustic wave generation spanning MHz-THz frequencies, including study of viscoelastic media at acoustic frequencies up to 100 GHz and combination with dynamic mechanic analysis down to the mHz range (spanning 13 decades in all), as well as observations of the onset of shear wave propagation as viscosity is increased, will be reviewed. Recent advances in generation of nonlinear acoustic and shock waves, shock effects on ionic glasses, metals, and quantum crystalline phases, and nondestructive generation of GPa shocks will be described. On faster time scales, coherent excitation of optical phonon and magnon modes and the resulting nonlinear responses measured on tabletop optical systems and at femtosecond x-ray free-electron laser (XFEL) facilities will be discussed. Taken together, multimodal control over coupled degrees of freedom involved in phase transitions and other collective transformations is becoming possible. Collective coherent control is enabling exploration of complex multiphase landscapes, searches for “hidden” metastable phases, and real-time observation of far-from-equilibrium properties and dynamics.


Prof. Keith Nelson joined the MIT Department of Chemistry as an Assistant Professor In 1982 after completing his doctorate in Physical Chemistry at Stanford University in 1981 and a postdoctoral year at UCLA. His research interests are in ultrafast optics, coherent spectroscopy, and coherent control over collective dynamics and structure in condensed matter. won the 2021 William F. He won the Meggars Award from the Optical Society of America "for expanding the horizons of impulsive stimulated Raman scattering (ISRS) to the generation of intense tunable terahertz pulses, thus establishing new transient-grating techniques for a more effective application of time-domain coherent nonlinear spectroscopy in the study of condensed phase molecular dynamics.

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