The mysterious origin of lightning was uncovered thanks to a cool lab trick

Researchers trapped and charged single aerosol particles with lasers to better understand cloud electrification and lightning formation.

Researchers at the Institute of Science and Technology Austria (ISTA) have developed a new way to trap, hold and electrically charge a single aerosol particle using two laser beams. The method gives scientists a closer look at how tiny airborne particles gain and lose electrical charge, which could help explain how clouds become electrically charged and how lightning may begin.

Aerosols are tiny liquid or solid particles floating in the air. They are all around us, from visible pollen in spring to microscopic particles such as viruses. Some, like sea salt, can even be breathed in near the coast. These particles are also important for clouds because they provide surfaces on which water vapor can collect, making them an important part of weather and climate.

PhD student Andrea Stöllner, who is part of the Waitukaitis and Muller research groups at ISTA, studies ice crystals inside clouds. Since real cloud particles are difficult to study directly, she uses transparent silica particles as model aerosols in the lab. Although these particles are much smaller than natural ice crystals, they allow researchers to study how cloud particles build up and exchange electrical charge.

Working with former ISTA postdoctoral researcher Isaac Lenton, Assistant Professor Scott Waitukaitis and other collaborators, Stöllner helped build an experimental setup that uses two focused laser beams to create what are known as optical tweezers. These use tightly focused laser light to trap and hold microscopic particles without touching them. Scientists already use optical tweezers to measure tiny forces and the electrical charge of particles with high precision in liquids, air and even a vacuum.

In the experiment, laser beams pass through a series of mirrors before meeting inside a chamber where aerosol particles drift through the optical trap. An anti-vibration table reduces movement from the room and nearby equipment, allowing the researchers to keep a single particle steady enough for detailed measurements.

“The first time I caught a particle, I was over the moon,” Stöllner says as she recalls her Eureka moment two years ago, just before Christmas. “Scott Waitukaitis and my colleagues rushed into the lab and took a short glimpse at the captured aerosol particle. It lasted exactly three minutes, then the particle was gone. Now we can hold it in that position for weeks.”

Stöllner says it took nearly four years to reach that point, building on an earlier version of the setup developed by Lenton. The original goal was to trap a single particle, measure its electrical charge and study how humidity affected it. Instead, the researchers made an unexpected discovery. The laser used to hold the particle was also changing its electrical charge.

“Originally, our setup was built to just hold a single particle, analyze its charge, and figure out how humidity changes its charges,” explains Stöllner. “But we never came this far. We found out that the laser we are using is itself charging our aerosol particles.”

The team found that this happens through what is known as a two-photon process. Photons are tiny packets of light that make up a laser beam. When two photons are absorbed almost at the same time, they provide enough energy to remove one electron, which is a negatively charged particle found in every atom, from the silica particle. As electrons are removed one by one, the particle gradually becomes more positively charged. The researchers say their model of this charging process closely matches what they observed in the experiment.

“We can now precisely observe the evolution of one aerosol particle as it charges up from neutral to highly charged and adjust the laser power to control the rate,” Stöllner says.

The team also found that as the particle becomes more positively charged, it occasionally releases some of that charge in spontaneous bursts. They believe something similar could happen inside thunderstorm clouds, where collisions between ice crystals and larger ice particles transfer electrical charge.

Scientists know these charge exchanges are an important part of lightning formation, but exactly what triggers the first spark is still unknown. One theory suggests lightning begins at charged ice crystals, while another proposes that cosmic rays help trigger the process by creating charged particles that accelerate in existing electric fields. However, current understanding suggests the electric fields measured inside clouds appear too weak to fully explain how lightning starts.

Stöllner believes the new setup offers a way to test the ice crystal theory in greater detail by tracking how individual particles gain and lose charge over time. “Our new setup allows us to explore the ice crystal theory by closely examining a particle’s charging dynamics over time,” Stöllner explains.

Although the researchers use silica particles instead of real ice crystals, they hope studying these small-scale interactions will help reveal what happens inside storm clouds. “Our model ice crystals are showing discharges and maybe there’s more to that. Imagine if they eventually create super tiny lightning sparks—that would be so cool,” Stöllner says with a smile.

Source: ISTA, APS

This article was generated with some help from AI and reviewed by an editor. Under Section 107 of the Copyright Act 1976, this material is used for the purpose of news reporting. Fair use is a use permitted by copyright statute that might otherwise be infringing.

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Posted Monday 13 July 2026 at 3:57 pm AEST (my time).

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