Optimization and analysis of a primary mirror for a laser incoherent combining system

A primary mirror for a high-power laser incoherent combining system was designed and analyzed. Firstly, the material and the thickness of the primary mirror, it's supporting way and it's lightweight scheme were determined through theoretical analysis. Then, the thermal deformation of the primary mirror was calculated by the finite element method, and the topology optimization was executed according to thermal deformation results. Finally, the impact of gravity, base frequency and ambient temperature on the P-V value of the primary mirror was analyzed. The calculation results show that the temperature rise ΔT and the P-V value of the primary mirror gradually increase when irradiated by six lasers with a power of 10 kW over a greater amount of time. When laser irradiation time reaches 3 min, the temperature rise ΔT and the P-V value of the unoptimized primary mirror are 83.4 ℃ and 155 nm respectively, resulting in thermal deformation values in the irradiated area that are inconsistently affecting by the structure. Its D-value was about 1/6 that of the primary mirror. After topology optimization, the lightweight rate of the primary mirror was 54.5%, the thermal deformation value in the laser-irradiated area was consistent, and the P-V value of the primary mirror reduced to 1/3. The gravity deformation value of the primary mirror at different pitching angles was basically the same and the maximum P-V value was less than 10 nm. The ambient temperature causes distortion and defocus aberration, and with an increase in ambient temperature, the aberration grows. Modal analysis shows that the base frequency of the primary mirror meets the system requirement. These conclusions have a referential value for high power laser incoherent combining systems.