FIGURE 2. Electronic coherence beating.

a, A representative two-dimensional electronic spectrum with a line across the main diagonal peak. The amplitude along this diagonal line is plotted against population time in b with a black line covering the exciton 1 peak amplitude; the data are scaled by a smooth function effectively normalizing the data without affecting oscillations. A spline interpolation is used to connect the spectra; the times at which spectra were taken are denoted by tick marks along the time axis. c, The amplitude of the peak corresponding to exciton 1 shown with a dotted Fourier interpolation. d, The power spectrum of the Fourier interpolation in c is plotted with the theoretical spectrum showing beats between exciton 1 and excitons 2–7.