Apparatus for deflection of a beam of light includes a case, which is configured to be positioned in a path of the beam, and a liquid, which is contained within the case. An array of plates is disposed across a surface of the liquid. The plates are configured to rotate on the surface about respective axes, which are mutually parallel and are spaced apart by a predefined pitch. An actuator is configured to drive a rotation of the plates about the respective axes so as deflect the beam that is incident on the plates.