Narrow-linewidth external-cavity blue diode laser pump source for pumping Pr³⁺-doped crystal

Diode lasers are indispensable pump sources for rare-earth-ion-doped solid-state lasers. In this work, aiming at the fundamental requirements of high power, narrow linewidth, and wavelength tunability, a blue diode laser pump source was developed by spatially combining 12 TO9 blue laser diode emitters and incorporating a Littman-Metcalf grating external cavity. A multi-longitudinal-mode rate-equation model based on the Lang-Kobayashi framework was established to investigate the longitudinal-mode competition and linewidth-narrowing mechanism of blue laser diodes under grating feedback. Experimentally, guided by mode-matching analysis, a symmetric concave-concave resonator was constructed for pumping a Pr:YLF crystal. The results show that the grating external-cavity blue pump source achieved wavelength locking at 443.9 nm over the entire operating current range, with a linewidth of 0.16 nm and a stable output power of 34 W. When applied to Pr:YLF pumping, this pump source enabled a maximum red-laser output power of 11.7 W, corresponding to a system optical-to-optical conversion efficiency of 36.6%, the beam quality factors were M _x ²=1.68 and M _y ²=1.22. This work provides an effective approach for improving the output power and pump conversion efficiency of visible solid-state lasers.