Ultraviolet intracavity frequency-doubled Pr³⁺:LiYF₄ orbital Poincaré laser

Here we demonstrate intracavity frequency-doubling of an ultra-compact (cavity length < 20 mm) Pr³⁺:LiYF₄ (YLF) orbital Poincaré laser, in which the fundamental modes are represented on an equivalent orbital Poincaré sphere (eOPS) and a singularities hybrid evolution nature sphere (SHENS). The generated ultraviolet (UV, 320 nm) output carries orbital angular momentum (OAM), and it typically exhibits an optical bottle beam with a 3-dimensional dark core, formed of a coherent superposition of eigen Laguerre-Gaussian (LG) modes. Such ultraviolet structured light beams with OAM offer many advanced applications from microscopy to materials processing.