Ultrafast science is the study of processes in atoms, molecules, or materials that occur in millionths of a billionth of a second or faster. This timescale is called femtoseconds, which is equivalent to 10-15 seconds. With ultrafast science, researchers use short pulses of photons, electrons, and ions to probe matter. Femtosecond X-ray pulses can produce stop-motion pictures of how atoms move during molecular transformations or how they vibrate on thin film surfaces. This timescale allows scientists to investigate the details of how processes fundamental to life change over time. For example, they can study how chemical bonds break and form and how excited electrons reshape the energy landscape of materials transformations.
Newer tools can produce pulses of duration in the hundreds of attoseconds (10-18 seconds). These even faster pulses enable scientists to track how electrons move when they are excited in chemical reactions.
Scientists for the first time tracked ultrafast structural changes as ring-shaped gas molecules unraveled after being split open by light. The measurements were compiled in sequence as the basis for computer animations showing molecular motion. Credit: Video courtesy SLAC National Accelerator Laboratory
Ultrafast science experiments increase our understanding of how atomic, electronic, and magnetic structures move and change on fundamental time scales. They also help us link those results to materials and chemical properties. Scientists studying these phenomena gain new insights on how to design materials with new properties and more efficient chemical processes.
Ultrafast Science Facts
- The development of X-ray free electron lasers is a breakthrough for ultrafast science.
- Ahmed Zewail was awarded the 1999 Nobel Prize in Chemistry for inventing “femtochemistry.”
- In one femtosecond, light travels just 300 nanometers, a distance comparable to the size of a virus.
- A femtosecond is to 1 second as 1 second is to 30 million years.
- To date, the shortest X-ray laser pulses delivered by LCLS last 5 femtoseconds, about the same time a molecule takes to lose an electron.
- Most ultrafast experiments involve the narrow time pulse capability of optical lasers. These laser pulses can then be converted into other kinds of pulses. The result is that researchers can tailor experiments choosing pulses from a selection of electromagnetic radiation energy (including X-rays), and particles such as electrons.
- The most common form of ultrafast experiment involves a “pump” pulse to excite the material to be investigated, and after a selected ultra-short time delay, a “probe” pulse to measure a feature in the sample. Scientists vary the time delay and measure the time history of the excited state as the system returns to equilibrium. The pump and probe can be different types of pulses, depending on the type of excitation desired and the type of property to be measured.
DOE Office of Science: Contributions to Ultrafast Science
The DOE Office of Science, Office of Basic Energy Sciences (BES) invests in fundamental research and user facilities for ultrafast science. This research includes fundamental investigations of changes in materials’ electronic structure and the flow of energy in new materials and chemical systems. The Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory is a premier facility for ultrafast science research. LCLS was the first hard X-ray free-electron laser in the world. It uses powerful flashes of X-ray light–each as brief as 5 femtoseconds and a billion times brighter than those available before–to take atomic snapshots. The LCLS will be even more powerful when SLAC completes work on the upgraded LCLS-II. Researchers string these together to create movies of chemical and physical processes. Insights into these fundamental, ultrafast motions could help solve some of the mysteries of the natural world and support the development of innovative materials, energy solutions, medicines, and more.