Utrafast Chemical Science Program
Overarching science goal: The Ultrafast Chemical Science Program at the SLAC National Accelerator Laboratory focuses on ultrafast chemical physics research at SLAC that is enabled by LCLS, the world’s first hard x-ray free-electron laser. The on-site presence of LCLS with its facilitating connections to our research is one of two distinguishing advantages of this FWP within the BES program. Our other distinguishing advantage is our close connection to the research powerhouse of Stanford University, through its Stanford PULSE Institute. These help to keep us competitive on a national and international level.
Funding Source: We are funded by the Atomic, Molecular, and Optical Sciences Program in the Chemical Sciences, Geosciences and Biosciences Division of Basic Energy Sciences in the Office of Science, Department of Energy. Jeffrey Krause is our DOE Program Manager.
• Imaging on the nanoscale in space and the femtoscale in time. Microscopy at its most essential level in both space and time is paramount to the BES mission to control matter. Non-periodic nano-structures and ultrafast timescales dominate the workings of biology and chemistry. To understand and control function we therefore must first observe structure and motion on these scales.
LCLS is a revolutionary x-ray source for investigations on the nanoscale, and our largest subtask is devoted to developing science using coherent x-ray imaging techniques at this and other x-ray free electron lasers. This work includes nanocrystal imaging on the few-Angstrom scale; nonperiodic imaging of single biomolecules; cell imaging; and imaging of aerosols.
• Light conversion chemistry. Light from the sun is the primary source of energy on earth, and so we are exploring its conversion to electron motion and then to chemical bonds. Some molecules are particularly adept at this conversion and we would like to understand how they work. For example, we are especially interested in the process of photocatalysis within coordination complexes and similar materials.
Energy conversion is initiated by charge separation, and we know that the charge distribution of the electron and hole, as well as the presence of low energy ligand field excited states greatly influence the lifetime of optically generated charge transfer excited states. Still, the detailed mechanism for the excited state quenching remains unclear. New methods of linear and nonlinear spectroscopy, and especially x-ray spectroscopy involving short-pulse FEL’s, can help provide the answer.
• The eV scale in time, space, and field strength. This is the fundamental scale that determines structure and dynamics of electrons in molecules, and motivates advances in sub-femtosecond time-resolution and Angstrom spatial resolution in theory and experiments. To achieve an adequate view of the molecular realm with at this level, we must interrogate atoms with fields comparable to Coulomb binding fields, and on time scales set by the electronic energy splittings in atoms.
One method to reach this scale is through high harmonic generation. We will extend our use of this technique to higher energies and with greater control over the target molecule, to interrogate the detailed motion of the electrons. We are particularly interested in coupled motion of multiple electrons, that goes beyond the “single active electron” approximation that has dominated thinking about strong field laser-atom physics. New theoretical approaches are also required for this, and we are tackling these as well.
Professor Philip Bucksbaum, AMO Physics, Program Spokesperson;
Associate Professor David Reis, Nonlinear x-ray science, Deputy Spokesperson;
Assistant Professor Kelly Gaffney, Physical Chemistry;
Professor Todd Martinez, theory;
Research Scientist Dr. Mike Bogan, biochemistry;
Senior Research Scientist Dr. Markus Guehr, AMO science.
Space allocations: Most of our research activities take place in renovated space in the SLAC Building 40a Central Laboratory
Subtasks: These six key personnel are responsible for six subtasks, which represent six different areas of expertise:
1. UTS: Ultrafast Theory and Simulation (Martinez)
2. ATO: Attoscience (Bucksbaum, Guehr)
3. SPC: Ultrafast Chemistry (Gaffney)
4. NPI: Non-periodic X-ray Imaging (Bogan)
5. SFA: Strong Field AMO Physics (Bucksbaum)
6. NLX: Strong Field and Nonlinear X-ray Optical Science (Reis)
The broad backgrounds of our PIs provide needed synergy for effective collaborations in cross-disciplinary projects.
Support operations (finance, HR, safety, purchasing, travel) are directed by the Photon Science Associate Laboratory Director and the Chemical Sciences Director and their staff. They provide oversight and delegate the work to appropriate offices in the SLAC Operations Directorate or to the staff of the Stanford PULSE Institute.