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.