High‐Purity Lasing of Ultrahigh‐Order Optical Vortices Enabled by Cavity Degeneracy Lifting

ABSTRACT Off‐axis pumped laser is a simple and efficient approach for generating high‐order optical vortices. However, despite its apparent scalability, the mode order achievable has stagnated for decades due to the mode purity issue. Here we show that this limitation mainly arises from the mode‐family degeneracy of the cylindrically symmetric cavity, with which the Ince‐Gauss noise is inevitable. By introducing controlled astigmatism that breaks the cavity symmetry to lift the degeneracy, the mode purity of the off‐axis pumped laser can be enhanced significantly. Together with control of transverse‐longitudinal mode frequency degeneracy and cavity mode size optimization, this approach enables robust scaling to ultrahigh mode orders. We experimentally demonstrate HG 630,0 laser emission with high mode purity directly from the cavity and its transform of LG 0,630 optical vortex via astigmatic mode conversion. This work provides a clear route toward scalable high‐order structured‐light lasers.