Evaporating droplet as atomic model

The after its publication in one of the world’s most prestigious physics journals, Physical Review Letters.

The lead author is doctoral student Javier Marmolejo.

The experiment, with lasers, mirrors and other equipment, is set up in a corner of one of the labs at the Department of Physics.

Javier Marmolejo injects water vapor into the installation, thus capturing a micrometric droplet between the lasers.

The phenomenon is called optical levitation, says Dag Hanstorp, Professor of Nuclear Physics.

– The light enters the droplet and bounces around while the water evaporates. Each time that the droplet’s shrinking circumference corresponds to an integer number of wavelengths, the droplet flashes. The phenomenon is reminiscent of “the Whispering Gallery” in Saint Paul’s Cathedral in London, where one person can stand at one side of the dome and whisper to someone on the opposite side.

The flashing is similar to what happens when an electron is emitted from an atom that is lit up by light of varying wavelengths, Javier Marmolejo explains.

– In this way, the droplet is like an atom model that is enlarged 100,000 times. This is interesting in itself, but the flashing also gives us an image of how photons spread. The pattern formed by the flashing also reveals whether there are other substances in the droplet; each substance creates its own special lines which means that we are able to ascertain what these substances are. Thus, the discovery may also have practical applications, such as analysing pollutants in translucent fluids. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.130.043804.

The study has caused quite a commotion in the research community. In addition to being published in Physical Review Letters, the article was also chosen to be part of the Editors’ Suggestion, the journal's selection of particularly interesting texts.

The public media have also been interested. Javier Marmolejo has, for example, participated in the Swedish radio's p4.

– I was also on a 1.5 hour podcast from California, explaining about the water droplets.

But Javier Marmolejo’s discovery of the flashing droplet was purely coincidental.

– I was actually involved in a completely different project. But when I saw this phenomenon, I felt compelled to investigate, simply because it was so beautiful.

Titeln på artikeln i Physical Review letters är Fano combs in the directional Mie scattering of a water droplet.