Watt-level single-longitudinal-mode Hermite-Gaussian lasing in a unidirectional ring cavity.

We demonstrate watt-level single-longitudinal-mode (SLM) high-order Hermite-Gaussian (HG) mode lasing from an off-axis-pumped Nd:YVO4 laser with a unidirectional ring cavity. This configuration combines simple pump-position-controlled transverse-mode selection with a mature and efficient architecture for SLM operation, offering a practical route toward power-scalable SLM structured-light lasers. The intrinsic astigmatism of the ring cavity further constrains the eigenmodes, supporting high-purity HG lasing and independent tuning of the two mode indices through the pump position. At an incident pump power of 3.18 W, the maximum output power of the high-order modes reaches 1.14 W, with slope efficiencies above 30%. SLM Laguerre-Gaussian beams are also obtained through astigmatic mode conversion. The influence of output coupling on laser efficiency and mode purity is investigated, revealing their trade-off and providing a reference for further power scaling.