We present a mode-locked diamond Raman laser synchronously pumped by a mode-locked laser running at 532 nm and pulse duration 26 ps. The diamond laser generated up to 2.2 W of average power with output pulses of duration 21 ps at a yellow wavelength of 573 nm. The output pulse duration varied notably with small changes in cavity length and decreased to a minimum of 9 ps. The power and pulse duration behavior as a function of cavity length is explained well by a model that includes phonon dephasing and group velocity dispersion of the pump and Stokes fields.