Tm3+:YLF crystal has a high absorption peak around 792 nm which locates in the diode pumping range, and also has a cross-relaxation process that provides the possibility for each absorbed pump photon to produce to ions at higher laser energy level. Tm3+: YLF laser is very suitable as a pump source for Ho3+:YAG laser. This is due to the good overlap of the emission band of Tm3+:YLF and the absorption band of Ho3+:YAG, and the ability to produce a linearly polarized output. Furthermore, the refractive index of Tm3+:YLF decreases with temperature, leading to negative thermal lens effect, which is partially compensated by positive lens effect caused by convex end.