Shaping the Arago–Poisson spot with incomplete spiral phase modulation

The Arago–Poisson spot played an important role in the discovery of the wave nature of light. We demonstrate a novel way to shape the Arago–Poisson spot by partially twisting the phase fronts of the incident light beam. We use a spatial light modulator to generate the holographic gratings both for mimicking the circular opaque objects and for modulating the spiral phase profiles. For incomplete spiral phase of five- and tenfold symmetry, we observe the gradual formation of the on-axis bright spots upon propagation. Our results show that two fundamental but seemingly independent optical phenomena, namely, the Arago–Poisson spot and the orbital angular momentum (OAM) of light, can be well connected by changing the phase height ϑ gradually from 0 to 2π. The experimental results are well interpreted visually by plotting the Poynting vector flows. In addition, based on the decomposed OAM spectra, the observations can also be understood from the controllable mixture of a fundamental Gaussian beam and an OAM beam. Our work is an elegant demonstration that spiral phase modulation can add to the optical tool to effectively shape the diffraction of light and may have potential applications in the field of optical manipulations.