Design of ten-thousand-watt laser beam expander and research on the thermal effect

We present a primary off-axis reflective laser beam expander based on a spherical secondary mirror and a high-order aspheric primary mirror configuration. The system processes an input laser power exceeding 10 kW, with a beam diameter of 15 mm @1/e2, and delivers an expanded beam diameter of 60.4 mm @1/e2, with maintaining a compact weight of 2.9 kg. To address thermal effects during beam expansion, we employed an integrated opto-thermo-mechanical analysis approach, utilizing finite element methods to investigate the temporal evolution of optical characteristics under both normal incidence and near-field beam offset conditions. The primary mirror uses glass-ceramics, whereas two secondary mirror materials were evaluated: sapphire and glass-ceramics. Experimental validation was conducted on the sapphire secondary and glass-ceramics primary configuration at 10.11 kW laser power for 140 s operation. Maximum temperature rises reached 9°C (primary) and 14°C (secondary). With 4 mm near-field beam offset, the expanded beam maintained βmax=1.26, βavg=1.14, and the laser source exhibits an optical axis jitter of <8 μrad, and the beam-expanded optical axis variation remains below 25 μrad. This demonstrates that the beam expander is rationally designed with excellent high-power laser beam expansion performance and incident optical axis adaptability, providing references for the design and simulation of high-power (10-kW class) laser beam expansion, as well as for laser transmission beam quality and pointing control.