Laser-induced damage in ZnSe and ZnS under 100 fs (800 nm) and 2 ps (9.2 µm) Pulses

Zinc selenide (ZnSe) and zinc sulfide (ZnS) are widely used windows and lenses for high-power infrared lasers, yet their ultrafast laser-induced damage thresholds (LIDTs) remain inconsistently reported across wavelengths. We report LIDTs for optical grade ZnSe and ZnS using two pulse formats under similar experimental conditions: 100 fs at 800 nm (multi-shot) and 2 ps at 9.2 µm (single-shot). At 800 nm, we measure thresholds of 0.112 J/cm² (ZnSe) and 0.170 J/cm² (ZnS); at 9.2 µm we find 0.80 J/cm² (ZnSe) and 1.20 J/cm² (ZnS). We compare the data with the Keldysh-based strong field ionization model and to the Gamaly ablation criterion. The models reproduce the observed material damage threshold ordering (ZnS > ZnSe) and the increase in the damage threshold from the near-IR to the long-wave IR, tracing the transition from multiphoton‑dominated ionization at 800 nm to tunnel-ionization-assisted breakdown at 9.2 µm. The results provide practical fluence limits and a clear framework for specifying ZnSe/ZnS optics in high-power NIR/LWIR laser systems.