Amplification of intrinsic noise in a chaotic multimode laser system

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Abstract
The output intensity of an intracavity-frequency-doubled Nd: yttrium aluminum garnet (YAG) laser can exhibit chaotic variations under certain conditions. It has been predicted that the intrinsic noise due to spontaneous emission present in this laser system can be amplified by the chaotic dynamics. We report here the observation of noise amplification in a mathematical model of this laser system in a parameter regime that produces chaotic intensity variations. The amplification was observed in the evolution of the distribution of an ensemble of noisy trajectories, originating from identical initial conditions. The observed amplification occurred at a rate given by the largest Liapunov exponent and is consistent with the theoretical predictions of Fox and Keizer [Phys. Rev. A 43, 1709 (1991)]. However, anomalous amplification was also observed and occurred at a rate ∼10 times the Liapunov exponent. The mechanism for this effect is elucidated.