Fig. 2: Spectrograms (dB) of recorded return signals in the experiment.
From: Controlled beat-wave Brillouin scattering in the ionosphere
The spectrograms are averaged over the experimental cycles (Table 1 and Supplementary Figures 7–9). The pump signal is at \(f-{f}_{0}=0\) and the probe is the first downshifted line at \(f-{f}_{0}=\Delta f\) given in Table 2. Visible are several up- and downshifted sidebands attributed to nonlinear wave mixing in the ionosphere producing SEE escaping the ionospheric plasma.
