To fully describe even a monochromatic light field, one needs to specify its magnitude, phase, and polarization state, all as a function of spatial position. The requirement to specify the polarization is commensurate with the light being a vector field. However, in many optical systems and associated phenomena, the polarization is uniform throughout the field, and it is sufficient to consider the light as a scalar field with only its magnitude and phase being spatially dependent. In such systems, if one examines any cross-section through the complicated light field, one aspect of the light's phase distribution is immediately apparent. Throughout the cross-section there are positions of phase singularity where all phases meet, and around which the phase changes by 2Ï, in either a clockwise or anticlockwise direction.
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