Physics & Astronomy

Thermodynamics-Inspired Laser Beam Shaping Sparks a Ray of Hope

Thermodynamics-Inspired Laser Beam Shaping Sparks a Ray of Hope

Thermodynamics-Inspired Laser Beam Shaping Sparks a Ray of Hope

Joule-Thomson optical expansion. Left: The expansion of a dense, warm gas leads to a rapid drop in temperature, in which interactions between the gas particles cause an irreversible energy conversion. Right: Against a similar mathematical background, intense laser beams can ‘clean’ their profile on their own and can even be efficiently combined if they are allowed to propagate into a larger system such as a multi-core optical fiber. (Image Credit: University of Southern California / Giorgos Pyrialakos).Inspired by ideas from thermodynamics, researchers at the University of Rostock and the University of Southern California have developed a new method to efficiently shape and combine high-energy laser beams. Their findings were published online in the renowned journal “Nature Physics” on January 15, 2025.

Sharing History: Light and Thermodynamics

Ever since prehistoric humans tamed fire to drive away dangerous predators and illuminate otherwise dark dwellings, light and warmth have been our constant companions. The ability to control fire as a source of both took humanity from its humble beginnings to its first steps on other celestial bodies. Light was a very useful by-product of heat and could also transfer it. “Children quickly realize that a candle flame is not something to touch. Likewise, experimental physicists have to learn to keep their fingers out of laser beams,” jokes Professor Alexander Szameit from the University of Rostock. The connections between thermodynamics and optics are more profound than it seems at first glance. Professor Demetrios Christodoulides and his team at the University of Southern California in Los Angeles have recently shown that the same laws that describe the interplay between temperature, pressure and volume in gases also apply to the propagation of high-energy laser beams in complex media.

Illustration of the thermodynamics-inspired laser beam shaping process in optical thermodynamics research.

What Makes the Joule-Thomson Expansion Process so Special?

One of the best-known processes in thermodynamics is the so-called Joule-Thomson expansion. Dr. Matthias Heinrich, a research associate in Szamei’s group, explains: “Imagine a spray can. As soon as the gas, which was previously trapped at room temperature under high pressure, leaves the opening, it can spread freely. It expands rapidly until the ambient pressure is reached, cooling down sharply in the process.” At the microscopic level, the interactions of the gas particles with each other lead to an irreversible energy conversion. Once it has expanded and cooled, entropy keeps the gas from returning to its original state.

In close cooperation with colleagues in Los Angeles and Orlando, the Rostock researchers were able to implement this process for intense laser radiation. Although light rays normally cross each other without interference, high intensity can lead to momentary changes in the medium. In this case, more light is not only brighter, but also behaves qualitatively differently. “This nonlinearity can be understood, in a very abstract way, as a counterpart to the interaction of gas particles. However, the effects are extremely tangible,” says first author Marco Kirsch, describing the starting point of his research. What the scientists interpret as the ‘temperature’ of the beam, however, has nothing to do with how ‘warm’ it would feel, but instead describes its shape. Kirsch adds: “By allowing disordered light distribution to ‘expand’ into a larger system such as a multi-core optical fiber, for example, a clean beam profile is formed through the associated ‘cooling’ without any external intervention.” In this way, even imperfectly tuned beams of several lasers could be combined into a common beam without significant energy losses – a breakthrough that can solve one of the biggest challenges in the construction of increasingly powerful lasers.

Light at the End of the Tunnel…

This successful international collaboration has significantly advanced the still young field of optical thermodynamics. Even though it may still be some time before these findings are translated into industrial applications, the physicists’ latest discovery points the way to innovative concepts, from the photonic counterpart of heat engines to heat pumps for light.

This work was funded by the German Research Foundation (DFG) and the Alfried Krupp von Bohlen und Halbach Foundation.

Expert Contact
Prof. Alexander Sameit
University of Rostock
Institute of Physics
AG Experimentelle Festkörperoptik
E-Mail ID: alexander.szameit@uni-rostock.de
Phone Number: +49 381 498-6790

Original Publication
Marco S. Kirsch, Georgios G. Pyrialakos, Richard Altenkirch, Mahmoud A. Selim, Julius Beck, Tom A. W. Wolterink, Huizhong Ren, Pawel S. Jung, Mercedeh Khajavikhan, Alexander Szameit, Matthias Heinrich & Demetrios N. Christodoulides
Journal: Nature Physics
Article Title: Observation of Joule–Thomson photon-gas expansion
Article Publication Date: 14 January 2025
DOI: https://doi.org/10.1038/s41567-024-02736-1

Media Contact
University of Rostock
Press and Communications Office
Universitätsplatz 1
18055 Rostock
E-Mail ID: pressestelle@uni-rostock.de
Phone Number: +49 381 498-1012

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