Observation of noisy precursors of dynamical instabilities

We have measured the power spectra of a periodically driven p-n junction in the vicinity of a dynamical instability. The addition of external noise introduces new lines in the spectra, which become more prominent as a bifurcation point is approached. The scaling of the peak, width, area, and line shape of these lines is measured near the onset of two different codimension-one instabilities: the period doubling and Hopf bifurcations. The results are in excellent agreement with recent theoretical predictions.