and amplitude $| {\bf A}_{\textrm{p} } |  =  10 \cdot 10^{-8}$ Js/(Cm). For this choice of pump-pulse intensity, the order parameter oscillations are close to resonance with the phonon frequency, i.e., $ | 2 \Delta_{\infty } / \hbar   - \omega_{\textrm{ph}} | \ll  \omega_{\textrm{ph}}$ \[Fig. \[FigM4\](f)\]. This leads to a beating behavior in the lattice displacement $U ( {\bf r}, t)$ [@Schny11]; see Fig. \[FigM4\](e). Correspondingly, we observe two distinct edges in the frequency dependence of $\sigma ( \delta t, \omega )$, one at twice the asymptotic gap value $\hbar\omega_{\Delta_{\infty}} = 2 \Delta_{\infty}  =2.2491$ meV and one at the phonon energy $\hbar\omega_{\text{ph}}=2$ meV \[blue and red traces in Fig. \[FigM4\](a)\]. The maxima of these two edges show an oscillatory behavior as a function of delay time \[Figs. \[FigM4\](b) and \[FigM4\](c)\], reflecting the nonadiabatic dynamics of both the phonon mode and the Bogoliubov quasiparticles.

The delay-time evolution of $\textrm{Re} [ \sigma(\delta t, \omega) ]$ at $\omega_{\Delta_{\infty}}$ is well described by Eq. (\[eq:fit\_1\]), as evidenced by the good fit in Fig. \[FigM4\](b). That is, $\textrm{Re} [ \sigma(\delta t , \omega_{\Delta_{\infty}}  ) ]$ oscillates with frequency $\omega_{\Delta_{\infty}}$ and an amplitude decaying as $1 / \sqrt{ \delta t}$. The oscillations at $\omega_{\textrm{ph}}$, on the other 