The Profilometer Guide: Contact vs. Optical Methods

A profilometer is the primary instrument used to measure surface texture. Selecting the right technology depends on your material, required resolution, and budget.

1. Stylus Profilometer (Contact Method)

The stylus profilometer is the "standard" method defined in most ISO and ASME standards. A diamond-tipped stylus is dragged across the surface, and its vertical displacement is recorded.

Advantages

  • Direct physical measurement (Gold Standard)
  • Not affected by surface color or transparency
  • Long scan lengths (up to 200mm+)
  • Lower cost for entry-level units

Limitations

  • Potential to scratch soft materials
  • Stylus tip radius (typically 2µm) acts as a mechanical filter
  • Slow (2D line profiles only)
  • Fragile stylus can be easily damaged

2. Optical Profilometers (Non-Contact)

Optical methods use light instead of a physical probe. They are essential for 3D (areal) measurements and fragile surfaces.

White Light Interferometry (WLI)

WLI uses the interference pattern of light waves to measure height. It offers incredible vertical resolution (sub-nanometer) regardless of the magnification.

Confocal Microscopy

Confocal systems use a pinhole to block out-of-focus light. They are excellent for surfaces with high slopes and varying reflectivity.

3. Technology Comparison

FeatureStylus (Contact)Optical (Non-Contact)
Vertical Resolution~1 nm~0.1 nm (WLI)
Lateral ResolutionLimited by tip radius (2-5µm)Limited by light (0.3-1µm)
Data Type2D Profile (Line)3D Areal (Map)
SpeedSlow (mm/sec)Fast (Seconds for full area)
Surface TypesOpaque, HardAll (Soft, Transparent, Complex)

4. How to Choose?

Decision Framework

  • 01Use Stylus if you need to measure deep inside narrow holes or grooves.
  • 02Use Optical if you are measuring soft polymers, biological samples, or wafers.
  • 03Use WLI if you need the highest possible vertical precision on mirror-like surfaces.
  • 04Use Stylus for simple pass/fail QC of Ra on the factory floor.