Light is a vector field often displaying a complex structure. Parameters such as amplitude, phase and the polarization, i.e., the direction of the electric field vector may change drastically in space even over sub-wavelength dimensions, giving rise to exotic properties such as phase singularities, polarization vortices and exotic angular momenta. These properties of light can be measured by letting it interact with sub-wavelength particles and detecting the scattered light. In reverse, by illuminating a small particle with properly designed light one can steer the scattered light and sensitively measure the particle position. These and related effects will be reviewed.
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