Spiral waves in a class of optical parametric oscillators.
The formation of three-armed rotating spiral waves is shown to occur in a spatially extended nonlinear optical system with broken phase invariance. These new spatial structures are found in the mean-field model of a class of optical parametric oscillators (3omega-->2omega+omega) in which the multistep process 2omega=omega+omega breaks the phase invariance of the down-conversion process. A parametrically-forced Ginzburg-Landau equation is derived to explain the existence of phase-armed spiral waves.
Longhi
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Dipartimento di Fisica, Istituto Nazionale di Fisica per la Materia, Politecnico di Milano, I-20133 Milano, Italy.