PULSE graduate student, Crystal Bray, a Ph.D. candidate in the Applied Physics department and a member of David Reis's group, will defend her thesis entitled, "Photon Energy and Carrier Density Dependent Dynamics of Electron Excited States Probed by Coherent and Squeezed Phonons in Select A7 Structures". Her defense will take place on Wednesday, August 12, 2015 at 9 am in the Paul Allen Building, Room 101X. Her abstract is printed below.
The interaction of intense femtosecond laser pulses with matter lead to highly excited transient states far from equilibrium. The dynamics of these excited states relate to many applications from laser machining to energy conversion. Ultrafast optical and x-ray light-scattering has emerged as a powerful experimental method to study material dynamics on the time-scale of atomic and even electronic motion. Here I report results of ultrafast coherent and squeezed phonon scattering experiments in bismuth and antimony. In response to laser generated coherent phonon scattering, I find the zone-center A1g vibrational mode greatly dependent on non-thermal electronic band-occupation. And in response to x-ray generated squeezed phonon scattering, I find anisotropic changes in dynamical forces evidenced by differentiated high wavevector acoustic mode softening. These results advance our understanding of microscopic electron-electron and electron-phonon interactions in transient systems.