  Coherent manipulation of quasi-particles is a crucial method to realize
ultrafast switching of the relating macroscopic order. In this letter, we
studied coherent phonon generation under strong light field which allows to
induce non-perturbative nonlinear optical phenomena in solids. The efficiency
of coherent phonon generation starts to saturate and deviate from the
pronounced linear power dependence when the light intensity goes into the
non-perturbative regime. We propose a novel theoretical model based on Floquet
picture and show that the saturation is due to a limitation of the driving
force inherent in non-resonant driving of the electronic system in the
non-perturbative regime.
