In surface morphology inspection, non-contact optical methodologies provide the same measurement results as a conventional contact profiler, but in a fraction of time.
The study used a Filmetrics step height standard coupon (left) and a non-calibrated roughness coupon for turning (N6-N10).
- Chromatic confocal
- Laser triangulation
- White light interferometer (WLI)
- Low coherence interferometry (LCI)
- Tolerant of surface specularity and translucence. Somewhat tolerant of surface contamination.
- Most optically tolerant of the optical sensors. Fast 2D measurements.
- Fast for 2D and 3D with larger field of view (FOV).
- Tolerant of surface reflectivity. Very high lateral resolution.
- Fast high resolution 2D measurements. Tolerant of surface reflectivity.
- Slow speed, surface damage and potential for cross contamination. Tip geometry limits or distorts surface morphology.
- May not measure steep specular surfaces.
- Low lateral resolution. Challenged by specularity, translucence and steep slopes.
- Generally small FOV. Requires stationary part. Slow for 3D.
- 2D only. Slightly lower lateral resolution than WLI.
The methods are equivalent in many cases where the surfaces are tolerant of all measurement types. The laser, confocal, LCI and WLI demonstrate equivalent performance for the spatial wavelengths studied, which are applicable for most machined surfaces. Differences may be observed at smaller wavelengths with fine ground or lapped surfaces.