Our research group at UC Berkeley studies the behavior of materials in extreme conditions. We focus on understanding how solids respond to high stress (up to a billion atmospheres of pressure, 1 GBar), the electronic structure of dense plasmas at temperatures of several million degrees, and also how simple molecules change configuration and break bonds when they absorb a photon of light. The natural world is a dynamic place and our research is concerned with measuring and controlling dynamics on the length and time scales of atomic and molecular motion (nanometers and femtoseconds). We study ultrafast phenomena in condensed matter, molecular, and atomic physics. Typically, we initiate dynamics by depositing energy with short-duration laser pulses, and then probe the resulting excited material using time-resolved X-ray scattering. The applications of our work extend from geophysics (what is the novel chemistry of materials under pressure?), to materials performance (can we design materials that don’t fail in extreme conditions?), to fusion energy (can we create plasmas that are at high enough density and temperature to undergo nuclear burn?).
At the Advanced Light Source synchrotron at Lawrence Berkeley National Laboratory we are determining the electronic structure of solid materials that are raised to temperatures on the order of the Fermi Temperature, where we test the boundaries of conventional solid-state theory and plasma theory.
At the large NIF laser at Lawrence Livermore National Laboratory we compress material to 10 times normal density at billion atmosphere pressures, and determine the equation of state of materials through dynamic radiography and inelastic x-ray scattering, on a platform that is designed for inertial confinement fusion experiments.
At the LCLS x-ray free electron laser at the SLAC National Accelerator laboratory we test fundamental plasma theories for example by measuring the lowering of the ionization threshold of atoms under dense and high temperature conditions.
At our tabletop laser system at Lawrence Berkeley National Laboratory, adjacent to the UC Berkeley campus, we study the energy and information flow in electronically excited molecular systems.
We often develop new tools and then apply them to a broad set of science problems. One of our tools is an ultrafast camera for measuring x-rays on picosecond timescales, called a streak camera, which helps us take pictures of materials as they evolve under high energy density or extreme conditions.
(a) Schematic of an X-ray Streak Camera (b) An image of a 60-ps x-ray pulse that is undergoing absorption in carbon; this picture displays the response to rapid heating, ionization, and plasma dynamics in a high temperature solid (foran example of this work see Phys. Rev. Lett. 106, 167601 (2011) or Sync. Rad. News 25, 12 (2012)).
Another tool we use is a pulsed vacuum ultraviolet and soft x-ray source based on high order harmonics generated from focusing an intense femtosecond laser pulse in rare gases.
Reference: T.K. Allison, et al., "Femtosecond Spectroscopy with Vacuum Ultraviolet Pulse Pairs," Optics Letters, Vol. 35, Issue 21, pp. 3664-3666 (2010).