Vrije Universiteit Amsterdam (VU), together with researchers from ARCNL and the Madrid Institute of Materials Sciences, has taken a significant step in better understanding extreme ultraviolet light (EUV light). The researchers demonstrate that the phase of the emitted light is strongly dependent on the intensity of the laser used.
This discovery could contribute to more accurate microscopes, more compact light sources for chip production, and new applications in nanotechnology and quantum technology. The results have been published in the scientific journal Science Advances.
On behalf of VU Amsterdam, former postdoc Nataliia Kuzkova and VU-group leader Peter Kraus were involved in the research via ARCNL, a joint research institute of Vrije Universiteit Amsterdam, the University of Amsterdam, and ASML.
Light from solid materials
In so-called high-harmonic generation (HHG), intense laser light is directed at a solid material. This creates new light with a much higher frequency, including EUV light. This type of light is important for applications such as advanced microscopes and the production of computer chips. A major problem until now has been that the emitted EUV light does not always stay in step with the original laser light. Different parts of the light beam also become out of sync with one another. As a result, the beam becomes less powerful and more difficult to focus sharply. Precisely this control over light is essential for future nanoscale technologies.
Although researchers already knew that the intensity of the laser plays a role in this, they had not yet succeeded in accurately measuring this effect and theoretically explaining it for solid materials.
Measurements on an attosecond scale
The researchers succeeded in measuring these phase differences extremely precisely, at the level of attoseconds—billionths of a billionth of a second. To do this, they used a very stable interferometric measurement method in which two EUV light waves are compared.
“The major challenge was being able to measure the phase of the light accurately enough,” says researcher Nataliia Kuzkova. “With our method, we were able to visualize changes on a timescale that was previously unattainable.”
Using extensive computer simulations and theoretical models, the researchers were subsequently able to explain why the phase changes when the laser intensity varies.
According to Peter M. Kraus, this is comparable to someone being pushed on a swing: “Normally, it is mainly the timing that determines where someone is in the movement. In our research, we saw that the force of the push also influences that position.”
Importance for chip technology and nanotechnology
The discovery helps researchers better understand why EUV light beams sometimes spread out and become less efficient. After all, the intensity in a laser beam is not uniform everywhere: the center is stronger than the edges. As a result, phase differences arise within the same beam.
Now that the origin of this effect is clear, researchers can take it into account in future experiments and possibly even actively correct it. This opens the door to more controllable EUV light sources.
In the long term, the results could contribute to technologies such as:
• more accurate microscopes for nanoscale research;
• more compact and efficient EUV light sources;
• improved techniques for the production of computer chips;
• applications in quantum technology and ultrafine electronics.
With this breakthrough, the researchers are taking an important step towards more controllable light for the technology of the future.
Website ARCNL: Phase and intensity closely linked in solid high-harmonic generation process