All pages tagged coherent structures

Understanding of the properties of nonlinear photonic systems is important both for the fundamental science and because of their relevance to numerous applications of light technology. Nonlinearity is an essential component in the design of numerous photonic devices, but it is often shunned by engineers in view of its practical intractability and greatly increased difficulty of comprehension of system behavior. The understanding and mastering of nonlinear effects can translate into improving performance of the existing devices and enabling a new generation of engineering concepts. However, many measurement techniques and signal processing methods have been developed and optimised for linear systems. Understanding of nonlinear dynamics would greatly benefit from new measurement approaches. I will review our recent works on the nonlinear science of fibre lasers, including spatio-temporal dynamics and new approaches for theoretical and experimental analysis of such systems.

The question of the relative importance of coherent structures and waves has for a long time attracted a great deal of interest in astrophysical plasma turbulence research, with a more recent focus on kinetic scale dynamics. Here we utilize high-resolution observational and simulation data to investigate the nature of waves and structures emerging in a weakly collisional, turbulent kinetic plasma. Observational results are based on in situ solar wind measurements from the Cluster and MMS spacecraft, and the simulation results are obtained from an externally driven, three-dimensional fully kinetic simulation. Using a set of novel diagnostic measures we show that both the large-amplitude structures and the lower-amplitude background fluctuations preserve linear features of kinetic Alfvén waves to order unity. This quantitative evidence suggests that the kinetic turbulence cannot be described as a mixture of mutually exclusive waves and structures but may instead be pictured as an ensemble of localized, anisotropic wave packets or “eddies” of varying amplitudes, which preserve certain linear wave properties during their nonlinear evolution.