Background Praseodymium-doped yttrium lithium fluoride (Pr:YLF) crystals are important gain media for visible lasers because they can generate multiple visible wavelengths under blue-light pumping. Visible lasers are useful in applications such as display, biomedicine, spectroscopy, and optical measurement. However, the output power of a single blue laser diode (LD) is usually low, which limits the available pump power and restricts the output power of Pr:YLF visible lasers.

Purpose This study aims to overcome the limited pump power from a single blue LD by combining multiple blue LDs. The objective is to obtain a high-power blue pump source while preserving the beam quality of the individual diodes, and then to achieve efficient high-power Pr:YLF laser operation at 639.5 nm through optimization of the laser system and output coupler.

Methods Spectral beam combining was adopted to combine nine blue LDs. This scheme increased the total pump power while maintaining the beam quality of each diode. The combined high-power blue light was then used to pump a Pr:YLF crystal. Parameters of the laser system and the transmittance of the output coupler were optimized to improve the visible laser performance.

Results With the spectrally combined blue pump source, high-power pumping of the Pr:YLF crystal was realized. When the pump power of the source was 20.75 W, a maximum output power of 8.04 W at 639.5 nm was achieved. This corresponds to an optical-to-optical conversion efficiency of approximately 38.7%, calculated from the given pump and output powers. The optimized laser system and output-coupler transmittance contributed to the improved visible laser output.

Conclusions Spectral beam combining of nine blue LDs effectively overcomes the low output power of single blue LDs for pumping Pr:YLF crystals. By combining high-power blue pumping with laser-system and output-coupler optimization, a 639.5 nm red laser with a maximum output power of 8.04 W was demonstrated. This approach provides a practical and scalable route for developing high-power Pr:YLF visible lasers and can be extended to other visible wavelengths and applications.