Figure 2

Uncalibrated single-pulse time domain signals measured in the plane of the ring are displayed in (a), and (c). The sign of the signals is flipped (indicated by the overlapping red and black curves) by illuminating opposite sides of the ring or reversing the circulation of the current in the ring. Associated normalized average power spectra (black) and standard deviation (red) are displayed in (b) and (d) for sample 1 (above) and sample 2 (below).