  As an alternative inertial confinement fusion scheme with predicted high
energy gain and more robust designs, shock ignition requires a strong
converging shock driven by a shaped pulse with a high-intensity spike at the
end to ignite a pre-compressed fusion capsule. Understanding nonlinear
laser-plasma instabilities in shock ignition conditions is crucial to assess
and improve the laser-shock energy coupling. Recent experiments conducted on
the OMEGA-EP laser facility have for the first time demonstrated that such
instabilities can $\sim$100\% deplete the first 0.5 ns of the high-intensity
laser pump. Analysis of the observed laser-generated blast wave suggests that
this pump-depletion starts at 0.01--0.02 critical density and progresses to
0.1--0.2 critical density. This pump-depletion is also confirmed by the
time-resolved stimulated Raman backscattering spectra. The dynamics of the
pump-depletion can be explained by the breaking of ion-acoustic waves in
stimulated Brillouin scattering. Such strong pump-depletion would inhibit the
collisional laser energy absorption but may benefit the generation of hot
electrons with moderate temperatures for electron shock ignition [Shang et al.
Phys. Rev. Lett. 119 195001 (2017)].
