Generation of ultraviolet optical vortex beams with independently controlled topological charge and central wavelength

The development of ultraviolet (UV) optical vortex beams is critical for advancing nanoscale photonic applications; however, it has long been hindered by fundamental limitations in high-performance UV optical components. In this study, we demonstrate a compact, two-stage nonlinear frequency upconversion architecture for generating UV optical vortex beams. The scheme integrates a synchronized dual-quasi-phase-matching process, where second-harmonic generation and sum-frequency generation processes occur concurrently, followed by a cascaded UV upconversion stage. This design enables independent control of the topological charge (TC) of the UV vortex beam and discrete, broadband wavelength selection across the deep- to near-UV spectral range. Experimentally, 269 nm femtosecond UV optical vortex pulses with a TC controllably tuned from ℓ = 1 to ℓ = 4 were generated. Moreover, by selecting distinct cascaded upconversion pathways enabled by the spatiotemporally synchronized multi-vortex output from the preceding SHG–SFG stage, discrete wavelength tuning from 241 to 407 nm was achieved. Collectively, this compact, two-stage nonlinear upconversion platform provides a robust and versatile route to structured light generation at short UV wavelengths.