An optical vortex, as one of the most prominent candidates for structured light, is typically identified as a phase or polarization singularity, resulting in a doughnut-shaped pattern and its carried orbital angular momentum (OAM). Due to the unique properties, the vortex fields are arousing ever-increasing interest among both the scientific and engineering communities because of their impressive and disruptive applications in a wide range of areas, from stimulated emission depletion (STED) nanoscopy to both quantum and classical OAM-multiplexed optical communications and more recently high-intensity vortex physics.

In the past decades, plenty of schemes were proposed for the generation of such unique structured light, including passive solution via a spiral phase plate, specially designed diffractive optical elements, cascading light converters, various fibers, metasurfaces, and also active generation directly from a laser cavity. However, it is only possible to practically generate an optical vortex with limited modal purity. In another word, it is never to expect to obtain a vortex with modal purity of 100% in experiments. Then, how to determine quantitatively the modal purity for an OAM structured field? In the past, a large number of works have also been devoted to addressing this challenge, such as mode decomposition, interferometric stages, and log-polar transformation.

Up to now, there remains one challenge at least: how to improve further the modal purity of OAM photons and how to exactly and dynamically measure the mode distribution in practice? Also, more exciting and promising applications are to be explored further in the future. Tremendous progress on this topic has been achieved in the past years while more are on the way.

In this Research Topic, high-quality Original Research, Review, and Perspective articles in these themes are all welcome. Research interests include but are not limited to the following areas:

1. New schemes for generation of vortex fields, not limited to optical waves, but extended also to the X-ray, gamma-ray, and terahertz (THz)-ray regimes, etc.
2. Generation of vortex beams directly from a laser cavity, including structured pumping vortex lasers, ultrafast vortex lasers, micro-/nano- vortex lasers, etc.
3. Novel vortex or vortex array fields, such as perfect vector optical vortex, specially designed vortex array, etc.
4. Various applications where the optical vortices are employed, such as OAM-multiplexed optical communications, vortex Lidars, new encoding schemes using this spatial degree of freedom, etc.
5. New phenomena and also novel physics involving the interaction between the vortex fields and matter, such as high-intensity vortex physics and OAM in second-harmonic generation.
6. Vortex propagation and stability in turbulent and scattering media, such as dense fog, water environment, etc.
7. Quantum systems involving OAM photons, e. g. for cryptography, quantum communications, teleportation, quantum imaging, etc.
8. Principle breakthroughs and practical techniques for measuring the mode composition and determining the modal purity, both for classical scalar vortices and vector vortices.
9. Devices and techniques for manipulation of OAM, e. g. for multiplication, division, routing, switching, multicasting, and other optical operations.

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