Damage dynamics and relaxation process of double pulses with nanosecond laser

The laser-induced damage threshold (LIDT) of optical elements is a critical limitation in advancing next-generation spaceborne laser technologies. Transient mechanisms in multiple-pulse damage dynamics have been recognized, but significant gaps remain in understanding these processes. In this study, we introduce a practice time interval (Δ t p )-dependent damage metric. Using a double-pulse double-probe experimental configuration, we systematically examine the double-pulse damage dynamics and relaxation process. The first pulse induces localized modifications that initiate a relaxation process, accumulating material damage caused by the subsequent pulse. Our results show that this relaxation lasts ∼500 ns for surface damage and is on a several millisecond scale for bulk damage. The second pulse induces more pronounced modifications and damage when Δ t p is less than 100 ns, dominated by nonlinear phenomena like multiphoton absorption due to temporally overlapping pulses. Conversely, for Δ t p >100 ns , thermal accumulation via phonon relaxation predominates. Additionally, the critical energy density for damage correlates positively with LIDT as Δ t p increases, reflecting the reduced thermal and mechanical stress influence. These findings highlight the dynamic competition between nonlinear and thermal effects in multiple-pulse laser interactions, providing practical strategies for designing optical components with high damage thresholds and developing high-performance optical systems.