Wide tuning of topological-charge vortex lasers generated by a single VCSEL-pumped Nd:YVO₄ crystal

Vortex lasers with tunable high topological charges serve as ideal light sources for spatial metrology and optical communications, providing significant improvements in displacement resolution and enhancing communication capacity. Also, compact, chip-scale solid-state lasers with optical vortices represent a critical frontier for integrated photonics. Here, we demonstrated, for the first time, a compact off-axis pumped thin Nd:YVO₄ vortex laser system utilizing a single-emitter vertical-cavity surface-emitting laser (VCSEL) as the pump source. The off-axis pumping configuration was implemented by actively controlling the tilt angles of the output coupler (OC). High-purity Laguerre-Gaussian (LG_0,±1) vortex lasers with distinct clockwise and anti-clockwise interference fringes were directly generated by synchronously tilting the OC in both the XOZ and YOZ planes. The vortex beams exhibited high mode purity (94%), quantified by a ring-to-center intensity contrast of 15.53 dB, and good beam quality with measured M² factors of 2.14 and 2.11 in the horizontal and vertical directions. Further controlled rotation of the OC enabled continued tuning excitation of diagonal high-order Hermite-Gaussian (HG) modes, spanning mode orders from n = 0 to n = 207. Moreover, vortex lasers with tunable topological charges (l) ranging from l = ±1 to l = ±207 were achieved using a π/2 phase converter, representing the highest reported tunable topological charge range for off-axis pumped vortex lasers. A chip-scale solid-state laser architecture capable of emitting both high-order HG modes and high-topological-charge LG vortex lasers (> 50th order) was also proposed, highlighting the potential for innovative integrated photonics applications.