LASERS

Encouraging instability

Phys. Rev. Lett. 120, 213902 (2018)

Parametric instability can occur in dispersive and nonlinear systems when a parameter of the medium is periodically modulated along the axis of wave propagation. The effect is sometimes called Faraday instability due to the great scientist’s observation of patterns formed in a fluid tank. Now, Auro Perego and colleagues in the UK, Russia, Spain and Italy propose that parametric instability can be self-induced in a fibre laser. The theoretical study uses the Ginzburg–Landau equation and coupled-mode analysis to predict the onset of self-induced parametric instability in a laser thanks to a periodic gain profile arising from pump injection into one side of a cavity. Due to the field structure in the cavity, the Stokes field resonating in the cavity ‘sees’ periodic gain and nonlinearity; if the gain passes a threshold, parametric instability occurs that leads to self-pulsing. The effect is theoretically analysed in a Raman fibre laser and the team hopes that it may ultimately yield pulsed fibre lasers operating at high repetition rates.

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Correspondence to David F. P. Pile.

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Pile, D.F.P. Encouraging instability. Nature Photon 12, 377 (2018). https://doi.org/10.1038/s41566-018-0208-2

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