Abstract

Angular momentum is of paramount importance in most branches of physics, including astrophysics, hydrodynamics, quantum optics and quantized particle ensembles. Despite the large literature on angular momentum, neither approaches has been developed to nonlinearly control it, nor thorough studies carried out on the role nonlinearity can play. Conversely, large attention has been devoted to the analysis of nondispersive wave-packets sustained by the interplay of dispersion (diffraction) and nonlinearity and, in particular, to deterministic clusters of two-dimensional solitons. Hereby we investigate the behavior of a two dimensional cluster of solitary waves, demonstrating - both theoretically and experimentally - an original technique to nonlinearly control its angular momentum. The theory, derived from first principles and with no specific assumptions on the material response, proves that the angular momentum of a soliton cluster linearly depends on excitation. We further show that angular momentum can be revealed by monitoring the rotation of the ensemble during a spiraling evolution: in an adiabatic regime, where the input power changes slowly, we predict that a linear change in angular momentum is accompanied by a linear variation in angular rotation of the cluster. We verify our results experimentally in nematic liquid crystals, i.e. a nonlinear non local medium supporting generation and propagation of stable two dimensional solitons.[2] Our sample is a 100μm layer of nematic liquid crystals pre-oriented in the (y,z) plane by anchoring, sandwiched between two glass plates (Fig. 1a). At the input, two solitons are excited with opposite momenta along x, compensating for walk-off Figures 1(b–g) summarize our experimental results: in agreement with theory, as the power is raised from 2.1 to 3.9 mW we observe a rotation of the soliton cluster owing to a change in its angular momentum (Fig. 1e–g).

© 2007 IEEE