Measurements of Finite-Bandwidth Effects on a Parametric Instability

The effects of a broadband (stochastic) pump on the parametric decay instability is studied experimentally. The growth rate decreases with pump bandwidth, $\Delta \omega$, as if only the fraction of the pump power within the resonance width is available to drive the instability, in agreement with theory. The saturated wave amplitude and suprathermal-electron production well above threshold are only slightly decreased (for bandwidths presently available, $\frac{\Delta \omega }{\omega }\lesssim 3\times {10}^{-3\mathrm{}}$) in agreement with simulation calculations.