Wavefront astigmatism sensing via spin–orbit coupling induced by a <i>q</i> -plate

The q-plate is a new type of polarization optical element with engineered optical anisotropy. New and wide-ranging applications, such as spin–orbit beam generation, angular momentum coupling, signal processing, and realization of holonomic polarization transformations in higher polarization topological index optics, are made possible by this novel element. In this paper, we demonstrate that q-plates can be used in optical metrology for testing astigmatic optical systems. A beam suffering from astigmatism is passed through a q-plate, and the signature intensity patterns obtained at the nominal focal plane are used to estimate the astigmatism.