Wednesday, August 28, 2019

ACS symposium - Chemistry in Real Space and Time

On Sunday I was fortunate enough to be able to speak at the first day of a week-long symposium at the American Chemical Society national meeting in San Diego, titled "Chemistry in Real Space and Time".  This symposium was organized by Ara Apkarian, Eric Potma, and Venkat Bommisetty, all from the UC Irvine NSF-supported center for Chemistry at the Space-Time Limit.  During its span as a center, CaSTL has been at the forefront of technique development, including integrating ultrafast optics-based time-resolved measurements with the atomic-scale precision of scanning tunneling microscopy.  The center is sun-setting, and the symposium is a bit of a valedictory celebration.

The start of our semester made it necessary for me to return to Houston, but a couple of highlights from the first day:

  • Pri Narang spoke about her group's efforts to do serious combined quantum electrodynamics calculations and microscopic nanostructure modeling.  If one wants to try to understand strong coupling problems between matter and light in nanostructures nonperturbatively, this is the direction things need to go.  An example.
  • Erik Nibbering talked about ultrafast proton transport - something I'd never thought about that depends critically on the positioning and alignment, say, of water molecules, so that hydrogens can swap their oxygen bonding partners.  His group uses a combination of photoacids (for optical control over when protons are released) and time-resolved infrared spectroscopy to follow what's going on.
  • Ji-Xin Cheng showed some impressive results of applying plasmon-enhanced stimulated Raman spectroscopy, basically tagging living systems with plasmonically active nanoparticles and performing pump-probe stimulated Raman to follow biological processes in living tissue. Very impressive hyperspectral imaging.  
  • My colleague Stephan Link showed some nice, clean results (related to these) in understanding chirality effects (trochoidal dichroism) in scattering of light by curved nanostructures, where the longitudinal component of the electric field (only happens at surfaces) is critically important.
  • Frank Hegmann and Tyler Cocker spoke about various aspects of THz-based STM.  I can't really do this justice in a brief blurb, but check out this paper and this paper for a flavor.  Similarly, Dominik Peller spoke about this paper and this paper, and Hidemi Shigekawa showed what you can do when you can achieve phase control over the THz light pulse.  Combining STM with femtosecond time resolution lets you see some impressive things.
  • While not STM, but none-the-less very cool, Yichao Zhang showed movies from the Flannigan group taken by time-resolved transmission electron microscopy, so that you can actually see the propagation of sound waves.  
Wish I could've stayed to see more - I felt like I was learning a lot.

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