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Brief Communications

Nature 402, 138 (11 November 1999) | doi:10.1038/45960

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Laser optics: Fractal modes in unstable resonators

G. P. Karman2,1, G. S. McDonald1,1, G. H. C. New1 & J. P. Woerdman1

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One of the simplest optical systems, consisting of two mirrors facing each other to form a resonator, turns out to have a surprising property. Stable resonators, in which the paths of the rays are confined between the two mirrors, have a well known mode structure (hermite–gaussian), but the nature of the modes that can occur in unstable reson-ant cavities (from which the rays ultimately escape) are harder to calculate, particularly for real three-dimensional situations1. Here we show that these peculiar eigenmodes of unstable resonators are fractals, a finding that may lead to a better understanding of phenomena such as chaotic scattering and pattern formation. Our discovery may have practical application to lasers based on unstable resonators1.