![]() "UED has been under development for the past 10 to 15 years, but the repulsive forces between electrons in the electron beam limited the time resolution of previous experiments," says the paper's first author Stephen Weathersby, the facility manager of SLAC's Accelerator Structure Test Area (ASTA), where the UED machine is installed. This animation explains how researchers use high-energy electrons at SLAC to study faster-than-ever motions of atoms and molecules relevant to important material properties and chemical processes. The whole apparatus works like a high-speed camera, capturing differences in diffraction patterns over time that scientists use to reconstruct the sample's inner structure and how it changes. The scattered waves then combine to form a so-called diffraction pattern picked up by a detector. When electron waves pass through a sample, they scatter off the sample's atomic nuclei and electrons. The method works because particles have a second nature: They also behave like waves. It spits out 120 of these bunches every second, generating a powerful electron beam that the researchers use to probe objects on the inside.īut how can scientists actually catch a glimpse of the interior of materials with particles like electrons? This electron source produces highly energetic electrons, packed into extremely short bunches. The superior performance of the new UED system is due to a very stable "electron gun" originally developed for SLAC's X-ray laser Linac Coherent Light Source (LCLS), a DOE Office of Science User Facility. 'Seeing' Ultrafast Processes with Electrons Both methods combined draw a more complete picture that will help researchers better understand and possibly control important ultrafast processes in complex systems ranging from magnetic data storage devices to chemical reactions. Yet, electrons interact differently with materials and "see" different things. Similar to X-ray light, highly energetic electrons can take snapshots of the interior of materials as they pass through them. The technique complements ultrafast studies with SLAC's X-ray free-electron laser. For example, it allows us to study chemical processes in the gas phase that are up to four times faster than those we can examine with current UED technologies." "Our apparatus delivers electron beams with a better quality than any other UED machine. "We've built one of the world's best UED systems to create new research opportunities in ultrafast science," says SLAC's Xijie Wang, who is in charge of developing the new instrument described in a paper published July 24 in Review of Scientific Instruments. It uses a method known as ultrafast electron diffraction (UED) and can reveal motions of electrons and atomic nuclei within molecules that take place in less than a tenth of a trillionth of a second – information that will benefit groundbreaking research in materials science, chemistry and biology. Credit: SLAC National Accelerator LaboratoryĪ new scientific instrument at the Department of Energy's SLAC National Accelerator Laboratory promises to capture some of nature's speediest processes. Changes in these diffraction images over time are used to reconstruct ultrafast motions of the sample’s interior structure. Then it travels through a sample and scatters off the sample’s atomic nuclei and electrons, creating a diffraction image on a detector. The beam gets accelerated by a radiofrequency field and focused by a magnetic lens. A pulsed electron beam is created by shining laser pulses on a metal photocathode. With SLAC’s new apparatus for ultrafast electron diffraction – one of the world’s fastest “electron cameras” – researchers can study motions in materials that take place in less than 100 quadrillionths of a second. ![]()
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