Physicists fight laser chaos with wave-dynamic chaos

  Physicists fight chaos with chaos

A Yale-led research team has chosen a new approach to stabilizing powerful lasers: they fight chaos with chaos.

There is a rapidly growing demand for powerful lasers for applications such as material processing, large-scale displays, laser surgery and light detection and measuring range sensors (LIDAR). A time-honored challenge for powerful lasers is taming their erratic pulsations and chaotic fluctuations of the emissivity and the beam profile. These problems hamper practical applications that require a stable, controllable laser light.

Previous strategies to reduce temporary fluctuations involved reducing the number of modes that the laser could use. As a result, none of the previous approaches are scalable to the power levels required for an increasing number of applications.

"We present a radically different approach based on the new principle of combating laser chaos with wave-dynamic chaos," said Hui Cao, principal investigator of a study published online in the journal Science on August 16th. Cao is the Frederick W. Beinecke professor of applied physics and a professor of physics at the Yale.

This video shows the numerically calculated field distribution in a D-shaped cavity and the measured emission from the straight segment of the cavity border:

"We use wave – chaotic or unordered cavities to disrupt the formation of self-organized structures such as filaments that lead to instabilities, "Cao said. "The laser instabilities are suppressed by chaotic cavity geometry.This approach is compatible with high-power operation, because it allows many spatial modes to be laser light at the same time."

Stefan Bittner, an associated research scientist from Yale and the first author of the study , said that the simplicity and robustness of the new system make it possible to apply broadly to other high-power lasers, including fiber lasers and semiconductor lasers. Moreover, he said, this new approach to suppressing instabilities and chaos with complex geometries can be applied to countless other unstable dynamic systems.

This video shows a typical trajectory of an optical system beam in a D-shaped cavity. The associated wavefronts create a complex interference pattern in the cavity:

Other Yale authors are Hasan Yilmaz and Kyungduk Kim. The research was carried out in collaboration with the theoretical group of Ortwin Hess at Imperial College London and the nanofabrication group led by Qi Jie Wang of the Nanyang Technological University in Singapore.

Yale's research was supported by the Office of Naval Research and the Air Force Office of Scientific Research.

Publication: Stefan Bittner, et al., "Suppression of spatiotemporal laser instabilities with wave-chaotic microcavities", Science 16 August 2018: eaas9437 DOI: 10.1126 / science.aas9437

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