Challenges and Strategies in Thermal Failure Resistance Assessment of Weak Absorption Materials under HPCW Irradiation

Accurate assessment of thermal failure resistance of weak absorption components is crucial for high-power continuous-wave (HPCW) laser systems. Conventional assessments, which predominantly rely on small-spot tests and irradiance equivalence, often overestimate component reliability. This study introduces characteristic temperature rise as the criterion, and investigates the thermal behavior of fused silica, BK7, and K9 across varying spot sizes through simulation and experiment. Results show strong spot-size dependence of thermal behaviors, and convergence of required irradiance at large spots. A criterion for the minimum representative spot size is established based on thermal diffusion mechanism, to ensure that the irradiance under this spot size remains within ±10% of the full-aperture values. The recommended minimum spot diameters are 14 mm for BK7/K9, and 15 mm for fused silica to represent the real thermal tolerance. This work provides a reliable assessment method for thermal performance of weak absorption materials in HPCW systems.