Wide Tunable Wavelength, High Topological Charge Perfect Vortex Beams Based on Carbon Dot Lasers

Vortex beams (VBs), with their unique spatial light field distribution, show promising applications in fields such as optical micromanipulation and high-capacity optical communications. However, the simultaneous realization of broad wavelength tunability and high topological charge remains a great challenge. In this work, based on the gain media of fluorescent carbon dots, which are known as a class of solution-processable and biocompatible materials with luminescence spectra covering from ultraviolet to near-infrared, perfect vortex beams (PVBs) with a wide wavelength tunability of up to 15 nm and a high topological charge of up to 50 have been realized for the first time. A combined strategy using double-beam interference pumping and a spatial light modulator (SLM) was proposed. Results show that the radii of the PVBs are independent of the number of topological charges but vary with the laser wavelength. While they can also be flexibly tuned by changing the period of the axicon and the focal length of the Fourier lens. Finally, a polarized PVB was successfully constructed by using a cascaded SLM, which further enriches the vortex mode properties of the carbon dot lasers. The results not only provide a new route for simultaneously improving the wavelength tunability and the topological charge of vortex lasers but also deepen the understanding of the mode properties of carbon dot lasers.