Regime 1 — Sublimation Ablation

Easiest laser cleaning application. High pulse energy (Netalux class) enables single-pass removal of thick rust. MOPA at moderate frequency equally effective with more passes.

Mill scale is denser than rust. Requires 3–5× higher fluence than red rust. Multi-pass or high pulse energy recommended.

Very low fluence effective. CW lasers highly efficient for large-area degreasing. Fume extraction required.

Fume extraction critical — combustion byproducts from rubber contain hydrocarbons. CW approach effective for heavy buildup on large flange faces.

Concrete dust and rebar geometry create access challenges. No vibration damage to surrounding concrete — key advantage over mechanical methods.

Heat tint is a thermally grown Cr₂O₃ / iron oxide multilayer (0.1–5 µm). MOPA at 50–100 kHz with 0.5–1.5 J/cm² removes tint without affecting passive film or base metal surface finish. Multiple low-fluence passes preferred over single high-fluence pass. Post-cleaning passivation recommended for food-grade or pharmaceutical applications.

Use minimum effective fluence. Do not exceed 1 J/cm² without substrate damage testing.

PVD/CVD coatings are highly adherent. Verify coating chemistry before attempting — TiN coatings absorb differently than TiAlN. Multiple passes at moderate fluence preferred over single high-fluence pass to control substrate heat input.

Titanium oxide scale from annealing or welding (alpha case / heat tint) typically 0.5–20 µm thick. MOPA at low fluence (1–2 J/cm²) with multiple passes is preferred over single-pass high fluence. Verify removal completeness with HF spot test or XPS — visible color change alone is insufficient.

Inconel oxide scales from high-temperature service are Cr₂O₃/NiO multilayers, typically 5–100 µm. High-energy Q-switched preferred for single-pass removal of heavy scale. MOPA effective for light oxidation. No substrate damage risk at fluences <10 J/cm². Common in aerospace MRO and power generation turbine blade refurbishment.

Granite's crystalline structure (quartz, feldspar, mica) responds well to 1064 nm laser cleaning. Lichen removal may require fluences approaching 2 J/cm²; atmospheric soiling and soot remove at 0.5–1 J/cm². Avoid rapid scanning over mica inclusions — differential thermal expansion can cause micro-fracturing.

Slate's laminar structure (phyllosilicate minerals) responds well to laser cleaning at moderate fluence. Primary application is architectural slate (roofing, flooring, cladding) and memorial stonework. Avoid high peak power on thin sections — thermal gradient can cause delamination along cleavage planes.

Concrete laser cleaning is primarily used for graffiti removal, paint stripping, and surface preparation before repair or coating. Aggregate type (silica vs. carbonate) affects local threshold variability. High-energy Q-switched effective for heavy coatings; MOPA suitable for light contamination and graffiti. Fume extraction required for lead-based paints.

Brick cleaning is primarily architectural conservation — soot from fires, industrial pollution, and salt efflorescence. Laser cleaning is particularly effective compared to pressure washing for heritage facades where water infiltration is a concern. Handmade and soft-fired bricks have lower damage thresholds than engineering brick.

Lime mortar (pre-1900 buildings) is much softer than Portland cement mortar and requires lower fluence. Portland cement mortar tolerates higher fluence. Primary use is facade cleaning where joint soiling is prominent. Avoid directing beam parallel to joint — can cause undercutting.

Primary application is selective removal of surface char from fire-damaged structural timber or decorative woodwork for conservation assessment. Low fluence, multiple passes preferred. Not suitable for general wood cleaning — mechanical or chemical methods typically more appropriate.

Laser paint stripping from wood is used in conservation (window frames, decorative millwork, historic structures) where chemical stripping would raise moisture content or mechanical scraping would damage profiled surfaces. 1064 nm absorption by wood is low — paint layer absorbs most energy. CO₂ laser (10.6 µm) achieves better selectivity for paint-on-wood.

Primary application: removal of built-up edge (BUE), oxidation scale, or PVD/CVD coatings from cutting tools and wear parts for reconditioning. High-energy Q-switched preferred for thick scale. MOPA effective for light oxidation or thin coatings. Cobalt binder has lower damage threshold than WC grains — avoid excessive fluence which preferentially ablates binder, weakening the composite.

Dense alumina ceramics (>95% purity) tolerate high fluence without substrate damage. Common applications: cleaning of alumina kiln furniture, semiconductor process components, and electrical insulators. Porous or lower-density alumina has reduced damage threshold — verify density before processing.

SiC absorbs 1064 nm via free-carrier absorption and defect states. Primary applications: semiconductor wafer carriers, mechanical seals, kiln furniture, and abrasive grinding wheels. SiC oxidizes to SiO₂ at high temperature — laser cleaning removes this SiO₂ oxide scale effectively. Reaction-bonded SiC (RB-SiC) has lower damage threshold than sintered α-SiC due to residual silicon inclusions.

Primary application is surface preparation for adhesive bonding and paint adhesion on aerospace structures, replacing chemical etching or abrasive blasting. Laser cleaning removes mold release agents, oxidized resin, and atmospheric contamination without fiber damage at low fluence (0.3–0.8 J/cm²). Above 1.5 J/cm², resin matrix begins to ablate — acceptable for intentional surface texturing but not for bond prep. MOPA at low frequency preferred for controlled shallow ablation.

Applications include marine vessel hull preparation, wind turbine blade maintenance, and automotive body panel prep. Gel coat removal is the most common use — the gel coat ablates at lower fluence than the underlying glass/resin composite. Key advantage over mechanical methods: no fiber damage, no abrasive contamination of the surface. MOPA preferred for gel coat removal; CW effective for large-area decontamination.