For over a century, light has both helped and limited our view of the tiny world. Microscopes use light to magnify cells, microbes, and nanomaterials—but light also behaves like a wave, and waves cannot be squeezed into spots smaller than their wavelength.
This diffraction limit has kept individual atoms largely out of reach for optical microscopes. Now, a team of researchers has found a way to overcome this problem.
Using an ordinary continuous-wave laser and a needle-sharp metal tip, they have pushed optical measurements down to about 0.1 nanometers, which is comparable to the spacing between atoms.
This “quantum leap pushes optical microscopy to length scales nearly 100,000 times smaller than what conventional light-based microscopes can resolve,” Valentin Bergbauer, one of the researchers at the University of Regensburg, said.
In simple terms, the researchers found a way to use light to probe matter at nearly the scale of single atoms, something that has been previously considered impossible.
Squeezing light into an atomic gap
The solution starts with a very sharp metal tip placed extremely close to a material’s surface. The gap between the tip and the sample is made smaller than an atom.
When they shine a continuous-wave mid-infrared laser on this setup, the light gets squeezed into that tiny gap and piles up at the very end of the tip. This already beats the normal diffraction limit and gives resolution around the size of the tip’s apex—about 10 nanometers, much better than regular microscopes, but still too coarse to see atoms.
However, when the researchers moved the tip even closer, something unexpected happened. The signal suddenly became much stronger and showed clear changes at Ångström (sub-nanometer) scales even though the system was driven by a gentle continuous-wave laser rather than powerful ultrafast pulses.
“At very small distances, the signal shot up dramatically. We didn’t immediately understand what was happening. The real surprise came when we realized we were resolving atomic-scale features down to 0.1 nanometers,” Felix Schiegl, lead researcher and a doctoral candidate at the University of Regensburg, said.
So why did this happen? Well, the reason comes from quantum physics. Even if the tip and surface are not touching, electrons can tunnel across the gap. The laser’s electric field shakes these electrons back and forth between the tip and the sample. Like tiny charges moving in an antenna, their motion produces a weak electromagnetic signal.
This allowed the researchers to detect this faint light, called near-field optical tunneling emission, using intensity-based optical measurements that directly reflect atomic-scale tunneling events.
“The decisive step is that we are no longer limited by how tightly light can be confined. Instead, we directly control and measure quantum electron motion confined to atomic dimensions,” Bergbauer added.
Opening the door to atomic-scale optics
This work suggests that optical tools can now explore distances once thought of as off-limits to light. Moreover, as the method works with standard continuous-wave lasers rather than expensive ultrafast systems, more labs could adopt it.
“Our findings enable the use of this tunneling-mediated contrast mechanism with standard optical setups, establishing a pathway to optical imaging with unprecedented resolution,” the researchers note in their study.
This could help researchers study how light interacts with matter at the level where many key processes actually begin—inside catalysts, semiconductors, quantum materials, and molecular electronics.
If successful, this approach could help scientists realize the dream of seeing and measuring the atomic world with light much closer to reality.
The study is published in the journal Nano Letters.