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.
