Modeling of beam quality control for the monolithic cavity diffusion-bonded Nd:YAG/Cr⁴⁺:YAG passively Q-switched...

This study establishes the criteria for achieving high-beam-quality output in monolithic, diffusion-bonded Nd:YAG/Cr⁴⁺:YAG lasers. In this monolithic architecture, the cavity mode size is constrained by the selected pump mode size, establishing a fixed pump-to-cavity mode size ratio. The high-beam-quality output can be ensured by maintaining a sufficiently low pump-to-cavity mode size ratio. In this work, a pump-to-cavity mode size ratio < 1.25 is determined to achieve an M² beam quality factor < 2. These findings are validated through comprehensive experimental analysis across diverse configurations. Furthermore, we investigate the feasibility of energy scaling by optimizing crystal length and mitigating thermal effects. This finding offers a framework for the design of high-performance, passively Q-switched monolithic lasers.