In-situ non-thermal plasma cleaning for large-aperture optics: Mechanisms, challenges, and applications

Non-thermal plasma (NTP) enables sub-nanometer precision, in-situ remediation of large-aperture optics, restoring atomic-scale cleanliness without compromising pristine substrate integrity—a capability unattainable by conventional wet chemistry. This review establishes a systematic framework linking the fundamentals of low-pressure plasma physics to targeted contaminant volatilization across four critical application domains: synchrotron beamlines, extreme ultraviolet (EUV) lithography collectors, tokamak diagnostics, and high-power laser transport systems. By deconstructing the interplay between plasma chemistry, plasma-surface kinetics, and material compatibility, we elucidate the governing principles for selective etching against diverse carbonaceous, metallic, and particulate residues. A cross-domain analysis further reveals three persistent engineering barriers: the reactivity-damage dichotomy, spatial heterogeneity across extended apertures, and hardware integration constraints within operational environments. Moving beyond empirical optimization, we outline a prospective trajectory toward autonomous, damage-free cleaning via advanced source architectures, closed-loop plasma diagnostics, and synergistic multi-field processing. Ultimately, this synthesis positions NTP cleaning as an enabling, scalable strategy for preserving absolute optical performance in next-generation precision systems.