= Equally spaced spectral components
For $N$ equal-intensity lines of spacing $\Delta\omega$, sum their correlations as a <geometric series>:
$$
\sum_{n=0}^{N-1}e^{-i(\omega_0+n\Delta\omega)\tau}
=e^{-i[\omega_0+(N-1)\Delta\omega/2]\tau}
\frac{\sin(N\Delta\omega\tau/2)}{\sin(\Delta\omega\tau/2)}.
$$
The <interferogram of an equally spaced spectral multiplet> has normalized visibility
$$
\mathcal V_N(\tau)=\left|\frac{\sin(N\Delta\omega\tau/2)}{N\sin(\Delta\omega\tau/2)}\right|.
$$
In the second original plot, full revivals occur at approximately $\tau=0,\pm100,\pm200\,\mathrm{ps}$, so
$$
\boxed{\Delta\omega=\frac{2\pi}{100\,\mathrm{ps}}\simeq6.28\times10^{10}\,\mathrm{rad\,s^{-1}},\qquad\Delta\nu\simeq10.0\,\mathrm{GHz}.}
$$
Between $0$ and $100\,\mathrm{ps}$ there are three zeros, near $25$, $50$ and $75\,\mathrm{ps}$, and two small subsidiary lobes. Since the model has $N-1$ zeros between adjacent revivals,
$$
\boxed{N=4.}
$$
The peak envelope of about $8$ and the intensity background of about $8$ are consistent with four equal components in the source's normalization, but the internal zero count is the useful shape-based check. The inference assumes the equal spectral weights represented by the graph; revival spacing alone does not fix the number of lines, and arbitrary unequal or hidden components would require more spectral information. Delayed self-interference measures spectral powers, not the relative phases between different source frequencies, so these revivals alone do not prove that the source emits a phase-locked pulse train.
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