Identify the degradation mechanism on BBO output facets

Identify whether hydrocarbon photochemistry on BBO crystal surfaces is a degradation channel during continuous-wave deep-ultraviolet operation near 230 nm.

Background

The paper discusses several coupled mechanisms that degrade BBO during prolonged continuous-wave operation near 230 nm, including absorption, color-center formation, heating, and surface contamination. Although carbonaceous films are established on deep-ultraviolet mirrors and windows, the authors state that such films have not yet been chemically identified on BBO facets. Consequently, hydrocarbon photochemistry remains a plausible but unconfirmed explanation for some surface degradation, making chemical identification and causal verification an unresolved issue.

References

We note, however, that whereas carbonaceous films are well established on DUV mirrors and windows, they have not yet been chemically identified on a BBO facet; hydrocarbon photochemistry on the crystal surface therefore remains a plausible but unconfirmed degradation channel.

— Robust watt-level continuous-wave deep-ultraviolet lasers near 230 nm  (2608.25544 - Cai et al., 26 Aug 2026) in Section 3.3, “Damage mechanisms and long-term mitigation”

These coatings are promising because they can both reduce Fresnel loss and protect the BBO surface from moisture and hydrocarbon adsorption. Their full long-term performance under high-power CW DUV exposure is still being evaluated.

— Robust watt-level continuous-wave deep-ultraviolet lasers near 230 nm  (2608.25544 - Cai et al., 26 Aug 2026) in Section 3.3, “Damage mechanisms and long-term mitigation”