From trace organic contamination to three-dimensional carbonaceous deposits: a non-equilibrium redeposition mechanism under nanosecond near-infrared laser irradiation

Laser-induced contamination limits the long-term reliability of optical systems, yet the formation pathway of carbonaceous deposits under nanosecond near-infrared (NIR) irradiation remains unclear. Here, tetradecane-contaminated K9 glass irradiated by a 1064 nm nanosecond laser is investigated using multiscale characterization and modeling. The irradiated surface exhibits a characteristic three-zone morphology consisting of a central depleted region, a peripheral carbonaceous deposition ring, and an outer pristine region. Atmosphere-controlled experiments show that deposits formed in air are substantially larger than those formed in nitrogen, with lateral sizes of approximately 39.2 μ m in air and 8–10 μ m in N 2 , accompanied by a much stronger nitrogen signal in air. AFM measurements reveal peak-dominated three-dimensional carbonaceous islands rather than continuous carbon films. Thermofluid simulations indicate that localized photothermal decomposition at the laser-heated center generates vapor- and droplet-state precursors that are expelled by recoil pressure and Marangoni-driven flow and subsequently redeposit on cooler peripheral regions. Kinetic Monte Carlo modeling further suggests that stochastic nucleation, surface diffusion, vertical stacking, and island coalescence govern the observed morphology. These results support a non-equilibrium redeposition mechanism, rather than direct in situ carbonization, for NIR laser-induced organic contamination. The proposed framework provides a physical basis for predicting and mitigating carbonaceous contamination in NIR optical systems.