This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: One big dream of ultrafast science has been to watch changes in nanoparticles or biomolecules on their natural timescale. Experimentally, this can be realized by taking two snapshots of the same object only femtoseconds apart.
However, no detector is fast enough to record the two snapshots separately—they end up on top of each other in a single image. Scientists now employ two complementary methods to disentangle two diffraction patterns captured by the same X-ray detector. The results by an international team of researchers have been published in two separate articles in Nature Communications.
A new capability of the European XFEL has recently enabled a big step toward the realization of nanoscale movies: The X-ray laser can produce successive flashes of two different colors that are bright enough to image a particle twice within femtoseconds. Both methods to disentangle two images take advantage of these different colors or photon energies: One method exploits the detector's capability to discern energy levels for each individual pixel, while the other uses mathematical reconstructions. Its inventors call the latter method dichography.
One of the leading scientists compares the technique to an extreme high-speed camera. "To my knowledge, these are the fastest nanoscale movies ever recorded, if by movie we mean multiple frames of the same object," says Alessandro Colombo from the Department of Physics at ETH Zurich in Switzerland. "This opens the door to observing rapid changes in nanoparticles, comparable to studies that have been possible with small molecules for some time now," says Yevheniy Ovcharenko, a scientist at the Small Quantum Systems (SQS) instrument at European XFEL and principal investigator of the study.
"These nanoparticles are less uniform than individual molecules, which makes it necessary to observe processes using the very same sample." Experiments on single molecules that follow chemical processes usually rely on series of observations of different samples at varying time delays after a trigger event. That approach does not produce precise results for particles that can differ in size, shape, orientation or internal structure. With two X-ray captures of the same particle, taken at a variable time delay, researchers can begin to follow a unique event directly, such as an expanding nanoplasma, a fragmenting cluster or a structural rearrangement triggered by light.
"We are at a starting point for a new type of study," adds Marcel Mudrich of the University of Kassel, who proposed the experiment together with his SQS colleague. "We now have free-electron lasers that can produce pairs of X-ray pulses with different 'colors.' We have detectors that distinguish between images based on the color of the scattered X-ray light, and we have the analysis tools to reconstruct the shape of individual particles from the recorded X-ray snapshots." To develop and prove the feasibility of the color-separation and dichography methods, the scientists used the SQS instrument at European XFEL. Two sections of the facility's undulators, X-ray light sources with a total length of 120 meters (394 feet), were tuned to different X-ray photon energies (about 1.0 and 1.2 kiloelectronvolts), or "colors," creating two X-ray pulses.
Extract — continue reading at the source.
