Laser doe ablation

Laser Ablation DOE

Operates under the rules in ../../INSTRUCTIONS.md (reference-first, reference-only, interactive mode).

When to use this skill

When the operator needs to develop a new ablation recipe — for a new material, new wavelength, or new geometric target. This skill enforces the surface → depth → volume progression from laser_ablation.md §12. Each stage has a defined experiment, and each experiment pauses for the operator to run it and report results before the next stage begins.

What this skill is NOT

• Not for cutting all the way through (use laser-doe-dicing).
• Not for joining (welding skill not built — yet).
• Not for diagnosing an existing recipe gone wrong (use laser-defect-diagnose).

References to load at start

• references/laser_ablation.md §4 (threshold), §9 (multi-pulse), §12 (workflow) — primary
• references/laser_process_calculations.md — fluence, peak intensity, focal spot
• references/gaussian_beam_theory.md — M², spot size derivation
• references/laser_optics_selection.md §5 — damage-threshold sanity check on chosen fluence

Inputs to gather first

Ask the operator:

1. Material — composition, surface state.
2. Goal — surface mark / shallow scribe / depth groove / drilled hole / area cleaning?
3. Tolerance constraints — kerf width, depth target, HAZ tolerance, throughput target.
4. Available laser — wavelength, max power, PRF range, pulse-width range, M².
5. Optical chain — focus-lens focal length, beam expander mag, focal-spot diameter (or input beam diameter so we can compute it via laser_process_calculations.md).
6. Throughput requirement — parts per hour or scan-speed target.

Compute and show derived values to the operator:

• Focal-spot diameter (from gaussian_beam_theory.md formula).
• Maximum single-pulse fluence at full power.
• Average fluence at mid-PRF.
• Whether any of these exceeds optic damage thresholds (per laser_optics_selection.md §5).

→ Pause: confirm all inputs and derived values. Address any damage-threshold flags before proceeding.

---

Workflow — 3 gated stages

Stage 1 — SURFACE: single-shot threshold

Per laser_ablation.md §12 Step 1.

What to do

1. Set parameters for non-overlapping single shots:
   • Low PRF (e.g., 1 kHz).
   • High scan speed so pulse-to-pulse spacing >> focal-spot diameter (e.g., 100 mm/s).
   • This keeps rise-time tail effects (scanner_optimization.md §6) out of the threshold reading.
2. Run a fluence sweep — typically 5–7 shots at logarithmically-spaced energies, bracketing the literature/estimated threshold.
3. Inspect the resulting craters under microscopy.

What the skill computes

• Required pulse-spacing for true non-overlap.
• Suggested fluence sweep range:
  • From any literature value the operator has (cite source explicitly — note that literature values are outside the reference docs and must be flagged as such).
  • From general material-class anchors when literature isn't available.
• Test-pattern parameter list (PRF, speed, pulse energies for each shot).

After running — Liu plot threshold extraction

Per laser_ablation.md §12:

• Operator measures crater diameter at each above-threshold fluence.
• Compute (crater diameter)² vs. log(fluence).
• Linear extrapolation crosses the x-axis at the ablation threshold fluence.
• Cross-check against any literature value.

The Liu plot can be built in the user's existing Process Parameters Calculator Liu Plot sheet, or computed by hand here.

→ Pause: confirm threshold value. Sanity-check against literature if available. Confirm to proceed to Stage 2.

Stage 2 — DEPTH: single line, log-spaced matrix

Per laser_ablation.md §12 Step 2.

What to do

1. Use the Stage 1 threshold as the lower-bound fluence anchor.
2. Build a Power × Scan Speed log-spaced matrix.
3. Mark the matrix as a grid of single lines on the same coupon.

Log-spaced series

Per laser_ablation.md §12 — use logarithmic spacing because the eye easily distinguishes 0.5 m/s from 1 m/s, but cannot reliably distinguish 4.5 m/s from 5 m/s.

The 1.6× series:

0.1, 0.16, 0.26, 0.41, 0.65, 1, 1.6, 2.6, 4.1, 6.5, 10, ...

• Power axis: span ~ 1× to ~ 5× threshold fluence (typically 4–6 levels).
• Scan-speed axis: span useful range (typically 4–6 levels).

What the skill computes per cell

• Fluence (J/cm²).
• Pulse-to-pulse pitch in µm.
• Multiple of ablation threshold.
• Optic damage check — flag any cell that exceeds the lens damage-threshold limit (with laser_optics_selection.md §5 + 2–10× safety factor).

Output

Generate the matrix as:

• CSV for now (simple, clean).
• Or markdown table for quick review.
• Excel output via shared library when lib/ppc_writer.py is built — eventually matching the Process Parameters Calculator column layout.

→ Pause: review the matrix before committing. Operator can edit cells, drop ones flagged as out-of-envelope, or expand the range.

After running

Operator inspects each line for cut quality, kerf, HAZ.

→ Pause: ask the operator to identify the best-quality cell at the highest scan speed that meets the requirements. That cell becomes the unit recipe for Stage 3.

Stage 3 — VOLUME: hatched area / multi-pass

Per laser_ablation.md §12 Step 3.

What to do

1. Take the unit recipe from Stage 2.
2. Apply across an area by stacking parallel lines at hatch distance (typically 0.5× to 1× spot diameter — same overlap math as laser_ablation.md §9).
3. For depth targets exceeding what one sweep clears, stack passes: 2× / 4× / 8× repeats.

What the skill computes

• Hatch overlap factor at the chosen hatch distance.
• Estimated depth per pass (calibrated from Stage 2 line cross-section).
• Estimated cycle time per area for each repeat count.

After running — the heat-accumulation diagnostic

Per laser_ablation.md §12 — Diagnostic.

Plot achieved depth vs. (number of repeats × inverse scan speed):

Relationship	Meaning	Action
Linear	Heat-tolerant process — doubling repeats halves speed-to-target	Use the highest-throughput cell. Done.
Non-linear (diminishing returns)	Strong thermal accumulation	One of: add Pause between passes (test 0.5 s, 1 s, 2 s); or lower per-pass power (drop one cell on the matrix).

→ Pause: operator reports which case it is. Loop with adjustment, or finalize.

---

Final output

The skill produces:

1. DOE matrix file — Stages 1, 2, 3 each as a sheet (CSV with stage labels for now; xlsx when ppc_writer is available).
2. Recipe summary (markdown) — final selected cell with all derived parameters, threshold value, validation samples, reference citations.
3. Reference index — which reference section drove each decision.

Save to outputs/laser-doe-ablation/<YYYY-MM-DD>-<material>/.

---

Cross-skill links

• If a defect appears in Stage 2 or 3 that the matrix can't explain → laser-defect-diagnose.
• If power readings drift during the experiment → laser-power-measurement (sanity check).
• If an optic damage check fires in Stage 2 → stop and warn (a laser-damage-sizer skill is planned but not built; for now, hand back to the operator with the warning).
• If position-specific defects appear (corner burn-in, line-end short) → laser-delay-tuner.