  Controlling the dynamics of mechanical resonators is central to many quantum
science and metrology applications. Optomechanical control of diamond
resonators is attractive owing to diamond's excellent physical properties and
its ability to host electronic spins that can be coherently coupled to
mechanical motion. Using a confocal microscope, we demonstrate tunable
amplification and damping of a diamond nanomechanical resonator's motion.
Observation of both normal mode cooling from room temperature to 80K, and
amplification into self--oscillations with $60\,\mu\text{W}$ of optical power
is observed via waveguide optomechanical readout. This system is promising for
quantum spin-optomechanics, as it is predicted to enable optical control of
stress-spin coupling with rates of $\sim$ 1 MHz (100 THz) to ground (excited)
states of diamond nitrogen vacancy centers.
