Optical device for the precision control of the electric field in the focus of a beam

We present a common-path optical device consisting of four optical components that produce a laser field consisting of two sub-beams with one radially polarized and the other linearly polarized. In the focus, the radially polarized sub-beam produces longitudinal polarization while the linearly polarized sub-beam produces polarization perpendicular to the propagation direction. By rotating the optical components, the orientation of the resulting electric field in the focus can be continuously varied in any direction. Estimates of the angular resolution of the device are given within the paraxial approximation.