Diode pumped alkali metal vapour lasers (DPALs) offer the promise of scalability to very high average power levels while maintaining excellent beam quality, making them an attractive candidate for future defence applications. A variety of gain media are used and each requires a different pump wavelength: near 852nm for caesium, 780nm for rubidium, 766nm for potassium, and 670nm for lithium atoms. The biggest challenge in pumping these materials efficiently is the narrow gain media absorption band of approximately 0.01nm.