321  W high-efficiency continuous-wave green laser produced by single-pass frequency doubling of narrow-linewidth fiber laser

In this study, a high-power continuous-wave green laser for copper processing is investigated. The laser is produced by single-pass second-harmonic generation (SHG) of a narrow-linewidth fiber laser. Based on Sellmeier equations, the factors (e.g., fundamental wave linewidth, temperature, and angle) that decide LBO noncritical phase matching are theoretically analyzed for optimizing the SHG setup. A narrow-linewidth polarization-maintained fiber laser is used as the fundamental laser with a linewidth of 20 GHz and polarization extinction ratio of greater than 15 dB. Type I noncritical phase-matching LBO is used as the nonlinear crystal in the SHG. A green laser (up to 321 W) is obtained from a 784 W fundamental laser with a conversion efficiency of 40.9%. The green laser is near-diffraction-limited and has a $ M^{2} $ factor of 1.07.