“In the field of laser technology, the research team constructed an LD end pumped concave flat resonant cavity based on the second threshold condition theory, using 1% (at.) c-cut Nd: YVO4 as the gain medium and Cr4+: YAG with an initial transmittance of 95.09% as the saturable absorber (SA). Key parameters such as output mirror transmittance, cavity length, collimation focusing lens focal length ratio, and focusing lens axial position were optimized. Experiments have shown that the gain loss balance of a resonant cavity is mainly determined by the output coupling transmittance and cavity length. Under specific conditions, a stable passive Q-switching output was obtained with an average power of 501 mW, a repetition rate of 217 kHz, a pulse width of 14.4 ns, and a time-domain jitter of ≤ 700 ns. This study provides a basis for applications such as precision machining, laser ranging, and nonlinear frequency transformation.”