High-brightness pulsed 476.8 nm blue laser via quadruple harmonic generation of a Tm:YLF MOPA

We present a high-brightness, nanosecond pulsed blue laser source at 476.8 nm through efficient quadruple harmonic generation from a Tm:YLF MOPA operating at 1.9 m.The fundamental-frequency stage produces 42 mJ pulses at 1907.3 nm with a narrow linewidth of 0.19 nm at 1 kHz.Through cascade second-harmonic generation using lowwalk-off LBO crystals, we achieve 10.52 mJ blue laser pulses with 16.1 ns duration, corresponding to a peak power of 0.65 MW and exhibiting excellent energy stability of 0.47%.The system maintains exceptional beam quality (M = 1.46,My = 1.27) at maximum output power, attributed to the negative thermal-optical properties of the Tm:YLF crystal, end-pumped amplification architecture, and optimized nonlinear conversion.This work demonstrates a compact and efficient route to high-brightness (~2.49GWcmSr) pulsed blue laser emission, particularly suitable for advanced marine scientific applications including underwater LiDAR and communication systems.