We demonstrated passive mode-locking of a Nd:YAG ceramic laser by optical interference modulation in a GaAs wafer. The combined effect of Kerr nonlinearity and optical interference in GaAs acted as an artificial saturable absorber and resulted in mode-locking. Maximum average output power of the mode-locked laser was as high as 2.84W, with a slope efficiency of 48%. The mode-locked pulse duration was as short as 4.1 ps. To our knowledge, this is the shortest pulse obtained from all Nd:YAG lasers without dispersion compensation.