Optical Coating Inspection Checklist (Free Template)

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Documents and traceability

Purchase order revision, drawing revision and specification revision match the received lot.CRITICALCertificate of conformance lists coating design, substrate material and lot or run number.CRITICALCoating run record or witness sample data is available for the lot.Substrate material certificate and index or homogeneity data are on file if the drawing calls for them.Quantity received matches the packing list and each part is identified or batch labeled.Drawing states surface quality, coating spec, wavelengths, angles of incidence and polarization.

Cosmetic and visual inspection

Inspection done under controlled lighting, against a dark background, with an agreed light level.CRITICALScratch and dig checked against the callout, for example per MIL-PRF-13830B or the ISO 10110-7 equivalent.CRITICALEdge chips, bevels and clear aperture are within the drawing limits.Coating is uniform in color across the clear aperture, with no streaks, haze or stains.No pinholes, voids, delamination, blisters or crazing under magnification.No fingerprints, residue or cleaning marks left on coated surfaces.Dimensional checks done: diameter, thickness, wedge and flatness as specified.

Adhesion and durability

Adhesion tape test performed on a witness sample or on a sacrificial part, with no coating removal.CRITICALModerate abrasion test (rub) performed if the specification requires, with no visible damage.Humidity or environmental exposure results reviewed for the lot, if required by the specification.Solubility or solvent resistance test performed if the design calls for it.Coating stress and substrate distortion within limits for thin or large optics.Durability test method and revision are recorded with results.

Spectral and optical performance

Reflectance or transmittance measured at the specified wavelengths, angle of incidence and polarization.CRITICALResults meet the drawing limit at every specified wavelength, with the measurement uncertainty considered.CRITICALSpectrophotometer calibration is current and the reference standard is recorded.Sampling plan stated (for example every part, a sample per run or per witness) and followed.Center and edge of the aperture measured if uniformity is specified.Scatter, absorption or wavefront error measured if the drawing requires them.Spectral plot saved and attached to the inspection record.

Laser damage and special requirements

Laser-induced damage threshold requirement identified, including pulse width, wavelength and test method such as ISO 21254.CRITICALLIDT data supplied from a representative sample of the same coating design and process.Low-absorption or low-scatter coatings have supporting test data when required.Special requirements like vacuum compatibility, outgassing or cryogenic cycling are confirmed.

Cleanliness, packaging and disposition

Parts packed in clean, non-outgassing, lint-free packaging with edge protection.Handled with gloves or finger cots, and in a clean area with clean tools.Labels show part number, coating, lot, quantity and any orientation marks.Orientation or coated side is marked where the design needs it.Disposition recorded: accept, reject, rework or return, with nonconformance number if applicable.CRITICALInspector name, date and gauge or instrument IDs are on the record.

Mark each item as pass or not. Any critical item that fails should stop acceptance until the issue is resolved or a documented deviation is approved. Adapt limits and test methods to your drawing, specification and customer requirements.

Receiving inspection plan for optics in your ERP

Optional: an expert review of mapping these checks to inspection characteristics and lot records.

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How to use the checklist

Work down the groups in order. Start with documents, since a wrong revision invalidates every measurement after it. Then do cosmetic inspection under controlled lighting, followed by durability checks on witness samples, spectral measurements against the drawing and any laser damage requirements. Tick each item as you go and note the disposition at the end. Items marked critical should hold the lot if they fail. Export the completed list to PDF or Excel and file it with the receiving or final inspection record.

Use the drawing as the source of limits, not memory
Record instrument IDs and calibration dates
Measure at the working angle and polarization, not just at normal incidence
Keep spectral plots with the record

Standards and methods behind the checks

Surface imperfections are specified as scratch and dig under MIL-PRF-13830B or the ISO 10110 part 7 system, and the drawing must say which. Coating durability tests such as the tape adhesion and moderate abrasion tests come from MIL-C-675C and MIL-C-48497A style practice and are often restated in company specifications. Laser-induced damage threshold testing follows the ISO 21254 series. Spectral performance is measured with a spectrophotometer using the calibration reference your quality system defines. Treat the standards as the structure of the check and use your own specification for the numbers.

What goes wrong in practice

Common problems are measuring at normal incidence when the part works at 45 degrees, where the polarization split is large, and accepting a certificate of conformance without a spectral plot. Another is inspecting under room light that hides haze. Cleaning with the wrong solvent or wiping a soft coating can damage it before the customer ever sees the part. Finally, a coating that passes at a witness position can differ from the production parts if the witness sat in a different place in the chamber.

Records and supplier feedback

Keep the completed checklist, the spectral plot and the lot number together so a field failure can be traced to a coating run. Feed rejects into supplier corrective action with the failing item, the measured value and photos of defects. Track the pass rate by supplier and coating design over time. In an ERP, the lot, inspection plan and nonconformance record are the natural anchors, and this checklist maps to the inspection characteristics on a receiving inspection plan.

Frequently Asked Questions

What does scratch-dig 60-40 mean?

It is a cosmetic grade under MIL-PRF-13830B: the first number is a scratch visibility rating compared against a standard, the second is the maximum dig diameter in hundredths of a millimeter. So 60-40 allows digs up to 0.4 mm. Lower numbers mean tighter cosmetics.

Why is the tape test performed on witness samples?

A tape pull can lift a weakly bonded coating and ruin the part. Testing a witness sample or a sacrificial piece from the same run shows adhesion quality without damaging shipping product.

Do I need LIDT data for every lot?

Usually not. LIDT is a destructive test and is typically qualified per coating design and process, then monitored by audit samples. Require it when the application is high-power, and require lot-level data only if your risk assessment says so.

Should reflectance be measured at normal incidence?

Measure at the angle of incidence and polarization the part will use. A coating that is excellent at 0 degrees can behave very differently at 45 degrees, especially for S and P polarization on beamsplitters and mirrors.

If coated optics arrive through your ERP receiving process, Netray can help connect inspection results, spectral files and supplier history to the lot, privately and on your own servers.

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