Researchers Unveil Plasma Lens to Enhance Attosecond Pulses

A team of researchers from the Max Born Institute (MBI) in Berlin and DESY in Hamburg has successfully developed a plasma lens that can focus attosecond pulses of light. This innovation notably increases the power of attosecond pulses used in experiments, offering new avenues for exploring ultrafast electron dynamics. The findings were published in the journal Nature Photonics on November 5, 2025.

Attosecond pulses, lasting just one billionth of a billionth of a second, are crucial for observing and controlling electronic movements in atoms, molecules, and solids. However, focusing these pulses—particularly in the extreme-ultraviolet (XUV) or X-ray regions of the electromagnetic spectrum—has posed significant challenges due to limitations in existing optical technologies. Traditional mirrors exhibit low reflectivity and deteriorate quickly, while conventional lenses absorb XUV light, leading to pulse distortion.

To address these issues, researchers at MBI and DESY generated a plasma lens by sending strong electrical pulses through hydrogen gas contained in a small tube. This process ionizes hydrogen atoms, producing a plasma where electrons migrate to the edges of the tube, creating a concave shape. Unlike typical lenses that disperse light, the plasma lens refracts light in a manner that effectively focuses attosecond pulses.

The study demonstrated that this plasma lens can focus attosecond pulses across various XUV wavelengths, with a tunable focal length determined by plasma density. Remarkably, the plasma lens achieved a high transmission rate exceeding 80%. Furthermore, it acts as an efficient filter for infrared driving pulses, eliminating the need for traditional metal filters and allowing a greater amount of attosecond power to be utilized.

The enhanced pulse strength opens up new possibilities for conducting attosecond experiments, which have historically been constrained by weak light sources. To investigate the temporal behavior of the focused pulses, the researchers performed computer simulations. They found that pulse stretching was minimal, increasing from 90 to 96 attoseconds. In conditions involving different colors arriving at slightly varied times—a phenomenon known as chirp—the plasma lens actually reduced the pulse duration from 189 to 165 attoseconds.

By successfully demonstrating the capabilities of an attosecond plasma lens, the research team has overcome a significant barrier in the field of attosecond science. This technique offers straightforward alignment, high transmission efficiency, and the ability to focus across various wavelengths. The implications of this breakthrough are vast, ranging from mapping electron dynamics in complex materials to advancing quantum technologies and facilitating the next generation of ultrafast microscopy.

For further details, refer to the publication by Evaldas Svirplys and colleagues titled “Plasma lens for focusing attosecond pulses” in Nature Photonics (2025).