Coherent short wavelength light for applications in probing highly-excited dynamics in nanoparticles and molecules

Tuesday, September 15, 2020 - 3:00pm

Virtual Photon Science Seminar

Speaker:  Quynh L. Nguyen, JILA/University of Colorado Boulder  

Program Description:

Ultrafast lasers and coherent short wavelength light sources from the UV to the X-ray region can capture  the fastest dynamics in molecules, nanoparticles, plasmas and materials. In my talk, I will first talk about  new high-flux tabletop vacuum ultraviolet source based on highly cascaded harmonic generation that can  probe reaction intermediates that are relevant to atmospheric science and combustion environments. 

I will then discuss ultrafast pump-probe photoemission spectroscopy to generate and interrogate warm  dense matter, which is a highly-excited state of matter that lies at the confluence of solids, plasmas, and  dense liquids. Its physical properties are critical for understanding matter in planetary science, astrophysics,  and fusion and plasma sciences. By exciting isolated ~8 nm nanoparticles with a femtosecond laser, we  can  create  uniformly-excited  warm-dense  matter,  and  heat  electrons  to  very  high  temperatures  ~10,000 Kelvin. Subsequent electron-ion heat exchange mechanism results in excitation of coupled phonon  modes  followed  by  non-thermal  melting  of  the  lattice.  We  measure  the  instantaneous  hot  electron  temperature and thereby extract the electron-ion coupling and hot electron cooling rates in warm-dense  nanomatter  for  the  first  time.  By  comparing  with  advanced  theories,  we  find  that  the  superheated  nanoparticles lie at the boundary between hot solids and plasmas with very strong electron-ion coupling.  Our in situ measurements demonstrate a new route for exploring the properties of matter in the warm-dense  regime and enable benchmarking for current state-of-the-art theories and future developments.  

 

Coherent short wavelength light for applications in probing highly-excited dynamics   in nanoparticles and molecules
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