Abstract
We present a comprehensive numerical study of (2+1)D counterpropagating incoherent vortices in photorefractive crystals, in both space and time. We consider a local isotropic dynamical model with Kerr-type saturable nonlinearity, and identify the corresponding conserved quantities. We show, both analytically and numerically, that stable beam structures conserve angular momentum, as long as their stability is preserved. As soon as the beams loose stability, owing to radiation or non-elastic collisions, their angular momentum becomes non-conserved. We discover novel types of rotating beam structures that have no counterparts in the copropagating geometry. We consider the counterpropagation of more complex beam arrangements, such as regular arrays of vortices. We follow the transition from a few beam propagation behavior to the transverse pattern formation dynamics.
Highlights
There has been a renewed interest in optical beams carrying angular momentum [1,2,3], ever since the realization that they can be associated with spatial optical solitons [4,5]
We present a comprehensive numerical study of (2+1)D counterpropagating incoherent vortices in photorefractive crystals, in both space and time
We follow the transition from a few beam propagation behavior to the transverse pattern formation dynamics
Summary
There has been a renewed interest in optical beams carrying angular momentum [1,2,3], ever since the realization that they can be associated with spatial optical solitons [4,5]. Of considerable importance in al-optical information processing, they come in a variety of forms - as bullets, screening, quadratic, photovoltaic, and lattice solitons, or as bright, dark, and grey [5,6] They are generated in different media, by different nonlinear mechanisms, but the self-focusing effect, produced by light-induced changes in the medium’s index of refraction, appears as a common thread to all mechanisms. In some of our publications [17,18,19] we presented a collision of two CP vortices carrying unit topological charges, as an example They were found to be unstable, generally breaking up into fragments within one diffraction length. We evaluate the dynamical conserved quantities for the CP vortices We show, both analytically and numerically, that stable beam structures conserve angular momentum, as long as their stability is preserved. The propagation of more complex CP beam arrangements, such as regular arrays of vortices, is considered, and the transition from a few beam propagation behavior to the transverse pattern formation dynamics is followed
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