Optical beams that carry Optical Angular Momentum, or OAM, are showing huge potential in several applications. For example, in optical communication the superposition of beams with different amounts of OAM can be used to create links with an astonishing Petabit per second capacity. However, in free-space links atmospheric turbulence typically degrades the signal, which limits the number of channels that can be reliably separated at the receiving end. This is where partial coherence can help. Beams that are somewhat random to begin with, are more resistant to the detrimental effects of turbulence than their fully coherent counterparts. So the combination of OAM and partial coherence promises to give us the best of both worlds. The state of coherence influences how a beam evolves on propagation. But in designing a beam with optimal properties, there’s a fundamental problem that one has to deal with: not all coherence functions that one can dream up are physically realizable. One type of beam that can and has been realized are so-called twisted Gaussian Schell-model (TGSM) beams. However, such beams always have a uniform correlation, severely limiting their range of design. Following recent theoretical work by Borghi [Opt. Lett. 43, 1627-1630 (2018)], Zhu and coauthors have now realized a new class of partially coherent twisted beams. By using a dynamic SLM holographic technique, a series of modes were produced in quick succession. Together these modes constitute a beam with the desired properties. This way Zhu et al. managed to produce beams that are non-uniformly correlated and that show interesting behavior on propagation such as self-focusing and rotation. This work opens the door to the design and generation of new forms of structured light.

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