Thermal analysis of high-power LD-pumped slab Nd:YAG laser

We have developed a high power LD pumped Nd:YAG laser using one zig-zag slab crystal, and obtained the average output power of 3.3 kW with the optical efficiency of more than 35% under the cooling condition of 12 degrees Celsius. Our method is to mount the LD stacks on both the sides of the 6 mm X 25 mm X 206 mm slab crystal in which the LD stacks mounted on one side of the slab pump the upper part of it while the ones on the other side pump the lower part. The LD pump light transmitted through the crystal is reflected by Au mirror and is introduced back into the slab. These LD stacks are arranged so that the thermally induced birefringence can be eliminated by maintaining uniform pumping in the width direction of the slab (non-zig-zag direction). The pumping distribution in the width direction was made constant by ray tracing simulation. The small signal gain distribution was measured constant in this direction, which indicates that the pumping distribution in the width direction has become uniform. The total heat generated in the slab was calculated to be less than 2.3 kW and the temperature distribution and thermal stress distribution were also simulated. According to this calculation, the maximum thermal stress of 40 MPa occurs in the surface of the slab, which is one-fourth of the fracture limit of YAG crystal.