Tabletop EUV–soft X-rays with a Wavelength You Can Tune

Tune the light. Explore the unknown.

 Published in Communications Physics, a Nature Portfolio journal

Tunable EUV–soft X-rays

X-rays have different “colours,” too – and choosing the right one can change what an experiment reveals. A new tabletop technique gives researchers greater freedom to make that choice, producing bright, laser-like extreme-ultraviolet and soft-X-ray light with continuously adjustable wavelengths.

Developed by researchers at TU Wien, the University of California San Diego and Few-Cycle Inc., the technique combines high brightness, sharply defined colours and the freedom to move between them. That means more control over the wavelength used to explore a material – and the details that can be brought into view.

The technique uses high-order harmonic generation, or HHG, to turn intense laser pulses into much shorter-wavelength light. Normally, the output comes in separate spectral peaks, leaving gaps between them. The wavelength an experiment needs can fall into one of those gaps. By carefully controlling how the driving laser pulses interact with gases and a crystal, the researchers shift the peaks smoothly across those gaps while keeping them narrow and bright. 

The driving laser’s colour also matters for brightness: shorter-wavelength pulses can generate high harmonics more efficiently, as demonstrated in earlier work with ultraviolet lasers [2]. The new technique uses carefully tailored visible pulses to combine efficient generation with continuous control over the emitted EUV and soft-X-ray wavelengths.                       

Tunable EUV Light up to the Aluminum Absorption Edge

What could that control reveal? Consider a tiny structure containing iron, cobalt and nickel. The light could be tuned to investigate each element’s magnetic behaviour, helping reveal patterns far too small to see with an ordinary microscope. Beyond showing what a material contains, it could be used to explore how its magnetic components behave and change. 

The possibilities also extend to nuclear-clock research. At suitable wavelengths, the approach could be used to investigate nuclear-clock candidates, searching for and mapping energy transitions inside atomic nuclei. These transitions could provide the “tick” for future precision clocks – linking control over light to new ways of measuring time.

From tiny magnetic structures to the inner workings of atomic nuclei, this wavelength-tuneable light – predicted to form trains of bursts lasting less than 300 attoseconds each – opens new ways to explore matter and follow its ultrafast changes.

Countless wavelengths. Endless possibilities.

For more information, please visit Ref [1].

 Cite as:

[1] D. Popmintchev, et al. Narrowband and wavelength-tuneable bright EUV–soft-X-ray harmonics for resonant imaging and spectroscopy. Communications Physics (2026). DOI: https://doi.org/10.1038/s42005-026-02791-5  

[2] D. Popmintchev et al. Ultraviolet surprise: Efficient soft x-ray high-harmonic generation in multiply ionized plasmas. Science 350, 1225–1231 (2015). DOI: 10.1126/science.aac9755