So-called extreme or rogue waves are large amplitude waves which appear unpredictably in optical and acoustic systems, in plasmas, as well as in quantum physics and in hydrodynamics. A key challenge is to understand the main causal factors behind such waves, which reflect a strong deviation from the normal distribution expected in any system of random waves. This understanding would be useful for learning to predict and control the occurrence of unexpected and potentially damaging large events.
In non-linear systems, many wave phenomena have been shown to be relevant for the generation of rogue waves, including many types of instability and sources of wave coherence capable of driving amplitude growth. Current research has emphasized such non-linear mechanisms, and implicitly dismissed the possibility that linear processes might be involved in anything other than short-term initial wave amplification. As a result, it remains an open question whether extreme, coherent structures can be generated even in principle from a small-amplitude random field by through purely linear interference.
In a new paper, however, LML External Fellow Fernando Metz and colleagues provide a positive answer to this question, demonstrating both experimentally and numerically how super-extreme waves can be generated by the simple linear superposition of random waves in an optical system. The authors show that, if the random phases of many wave exhibit long-range correlations in space, even linear interference generates waves with amplitudes as high as those observed in systems with strong non-linearities.
The paper is available as a pre-print at https://arxiv.org/abs/1912.13390