Physicists fight laser chaos with quantum 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 lasers can no longer be used for many practical high-power applications, such as in ultra-bright 3D 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’s School of Physics and Astronomy have come up with a new solution.

Their new 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.

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.

Co-author of the study Dr Sang Soon Oh, Ser Cymru II - Rising Star fellow in School of Physics and Astronomy part-funded by the European regional Development Fund through the Welsh Government, said: “Our approach to reduce the instabilities of a laser would sound counterintuitive at first, because we introduce chaos to make the laser more stable.”

“Our method is very powerful and applicable to various types of lasers since it does not require reducing the number of lasing modes. We believe our approach will find broad applications and open a new direction of research combining the concepts from both wave-dynamical chaos and deterministic chaos.”