Physicists fight laser chaos with quantum chaos to improve laser performance

August 16, 2018, Imperial College London
The D-shaped cavity producing quantum chaos within the cavity, and a more stable laser resulting. Credit: Bittner et al.

To tame chaos in powerful semiconductor lasers, which causes instabilities, scientists have introduced another kind of chaos.

High-powered semiconductor lasers are used in materials processing, biomedical imaging and industrial research, but the emitted light they produce is affected by instabilities, making it incoherent.

The instabilities in the laser are caused by optical filaments; light structures that move randomly and change with time, causing chaos. Removing these instabilities has long been a goal in physics, but previous strategies to reduce filaments have usually involved reducing the power of the laser.

This means it can no longer be used for many practical high-power applications, such as in ultrabright 3-D laser cinema or as elements in extremely bright laser systems used in fusion reactors.

Instead, researchers had to choose between a powerful semiconductor laser with poor output quality and a coherent but much less powerful laser.

Now, a research team from Imperial College London, Yale University, Nanyang Technological University and Cardiff University have come up with a new solution.

Their technique, published today in Science, uses 'quantum chaos' to prevent the laser filaments, which lead to the instabilities, from forming in the first place. By creating quantum (wave) chaos in the cavity used to create the laser, the laser itself remains steady.

Professor Ortwin Hess, from the Department of Physics at Imperial, contributed much of the theory, simulation and interpretation of the new system. He said: "The way the optical filaments, which cause the laser instabilities, grow and resist control is for the laser a bit like the unruly behaviour of tornadoes. Once they form, they move about chaotically, causing destruction in their wake.

A typical trajectory of an optical ray inside a D-shaped cavity. The associated wave fronts create a complex interference pattern in the cavity. Credit: Cao, Hess, et al.
"However, tornadoes are more likely to form and move about over flat country. For example, in America they form frequently in beautiful Oklahoma but not as often in hilly West Virginia. The hills appear to be a key difference—they prevent tornadoes from being able to form or move around.

"In the same way, by creating a 'hilly' optical landscape right inside our lasers using quantum chaos, we don't allow the filaments—our optical tornados—to form or grow out of control."

The laser system, manufactured at the Nanyang Technological University in Singapore, has been proven experimentally at Yale University. The team are now working to further explore and tailor the light emission, such as improving the directionality of the laser.

They say however that the breakthrough should already allow semiconductor lasers to work at higher power with high emission quality, and that the same idea could be applied to other types of lasers.

Lasers emit coherent light that can be focused in a tight beam. To produce and amplify the light, it is bounced around a cavity through special gain materials. However, when large are switched on, this bouncing back and forth creates filaments—sections of the light that swiftly begin to act chaotically.

The numerically calculated field distribution inside a D-shaped cavity and the measured emission from the straight segment of the cavity boundary. Credit: Cao, Hess, et al.

To create a different kind of chaos—the quantum chaotic landscape—the team designed a new shape of cavity for the laser. Most cavities are cuboid in shape, but by using a D-shaped cavity, the team were able to induce quantum chaos in the light bouncing around.

This quantum chaos acts on a smaller scale than the wavelength of the light, creating the optical 'hills' that help to dispel the optical 'tornadoes'.

Professor Hui Cao, from Yale University, said: "We use wave-chaotic or disordered cavities to disrupt the formation of self-organized structures such as filaments that lead to instabilities."

The team gained insight into the processes and cavity shapes likely to create this kind of quantum from theories and experiments in nanophotonics and nanoplasmonics—studying and metals at scales of billionths of a metre.

Professor Hess added: "I have been working on spatio-temporal and quantum dynamics in lasers since my Ph.D., so it is gratifying to return to it now with the knowledge gained from nanophotonics and nanoplasmonics.

"The relationship also works the other way around—with systems like this we can offer new insights into nanophotonics and nanoplasmonics, and bring the nanoscience and communities together."

Explore further: Quantum dot ring lasers emit colored light

More information: "Suppressing spatio-temporal lasing instabilities with wave-chaotic microcavities" Science (2018). … 1126/science.aas9437

Related Stories

Quantum dot ring lasers emit colored light

January 22, 2018

Researchers have designed a new type of laser called a quantum dot ring laser that emits red, orange, and green light. The different colors are emitted from different parts of the quantum dot—red from the core, green from ...

Laser cavities take on new shapes and functionalities

October 12, 2017

Researchers have demonstrated the first laser cavity that can confine and propagate light in any shape imaginable, even pathways with sharp bends and angles. The new cavity, called a topological cavity, could enable laser ...

Getting light in shape with metamaterials

July 27, 2016

Converting light from one wavelength (or "color") to a shorter wavelength, a process needed for efficient communication and advanced manufacturing, is typically inefficient. To tackle that inefficiency, a team built a specialized, ...

Recommended for you

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

How heavy elements come about in the universe

March 19, 2019

Heavy elements are produced during stellar explosion or on the surfaces of neutron stars through the capture of hydrogen nuclei (protons). This occurs at extremely high temperatures, but at relatively low energies. An international ...

Trembling aspen leaves could save future Mars rovers

March 18, 2019

Researchers at the University of Warwick have been inspired by the unique movement of trembling aspen leaves, to devise an energy harvesting mechanism that could power weather sensors in hostile environments and could even ...

Quantum sensing method measures minuscule magnetic fields

March 15, 2019

A new way of measuring atomic-scale magnetic fields with great precision, not only up and down but sideways as well, has been developed by researchers at MIT. The new tool could be useful in applications as diverse as mapping ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Aug 16, 2018
fighting laser chaos is no joke and should be taken with the utmost care. vive la resistance!
not rated yet Aug 17, 2018
very interesting research! would love to learn more about it...
not rated yet Aug 17, 2018
we offer free diode lasers 405 / 445 nm for researchers all over the world

Please email to if you are interested...

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.