Snapshots At The Atomic Level: New Imaging Increases Sensitivity

Using attosecond X-ray pulses, scientists have been able to increase the brightness and resolution of images of ultrafast processes in their natural environment.

The investigation of matter using X-ray pulses enables, among other things, structural analysis in the nanometer range. Increasingly stronger X-ray pulses have increased the resolution of this technique to such an extent that the sample is destroyed during the pulse. This has previously represented a fundamental limitation of the achievable resolution and could now change.A new study in Nature Communications shows that the duration – or rather the brevity – of the X-ray pulses makes a crucial difference.

An international research team has succeeded in generating pulses in the attosecond range using the free-electron laser (FEL) at SLAC National Laboratory in California. An attosecond is an extremely short unit of time - a billionth of a billionth of a second. For comparison: there are more attoseconds in a second than there have been seconds since the Big Bang. First author Stephan Kuschel, since 2023Professor of Laboratory Astrophysics at TU Darmstadt , explains: "These tiny time scales are crucial for making the movement of electrons visible, which takes place at incredible speed. X-ray pulses, as we use them, are ultra-short flashes of light in the X-ray range of the electromagnetic spectrum. They have extremely short wavelengths that release electrons from the atoms being studied through ionization. This enables us to research very small structures such as nanoparticles."

image quality significantly increased
Normally, ionization leads to electrons being lost and the scattering efficiency decreasing, known as "bleaching". The key lies in fleeting resonances that amplify the scattering by creating extremely short-lived excited states. By combining these resonances with pulses in the attosecond range, the researchers were able to exploit the ionization processes for a short time and amplify the scattering by up to ten times. "This significantly increased the image quality," says Kuschel, "both the spatial resolution and the brightness improved significantly."

The recordings amazed the scientists themselves, the signals in the experiments at the FEL were so unexpectedly strong. But strict quality controls and independently conducted simulations confirmed the measurements. Stephan Kuschel is delighted: "This approach opens up new possibilities for observing and exploiting ultrafast processes such as intra-atomic processes. This also benefits the investigation of chemical reactions and phase transitions in previously unattainable spatial and temporal resolution. The new technology offers enormous potential not only for basic research, but also for applications in materials science and nanotechnology."