  We present an experimental demonstration of a deterministic optical rocking
ratchet. A periodic and asymmetric light pattern is created to interact with
dielectric microparticles in water, giving rise to a ratchet potential. The
sample is moved with respect to the pattern with an unbiased time-periodic
rocking function, which tilts the potential in alternating opposite directions.
We obtain a current of particles whose direction can be controlled in real time
and show that particles of different sizes may experience opposite currents.
Moreover, we observed current reversals as a function of the magnitude and
period of the rocking force.
