▎ 摘　　要

Here we report on the exfoliation of graphene by using femtosecond pulsed laser with the highly oriented pyrolytic graphite (HOPG) immersed in water. The size of the graphene flakes was demonstrated to be well regulated by controlling the peak-power density of the femtosecond laser irradiation on the HOPG. The transmission electron microscopy (TEM) and Raman spectroscopy were used to identify the morphology and crystalline phase of the graphene. As an application, the few-layers-graphene absorber with a modulation depth of 0.5% was used in a passive Q-switched Nd: YVO4 laser. A Q-switched nanosecond pulse train with the maximum pulse energy of 262.35 nJ and the narrowest pulse duration of 131.6 ns was obtained.