White Light Interferometry
Is white light interferometry a contact measurement method?
No. It is a non-contact optical method that uses broadband light interference, making it preferred for fragile, soft, coated, or highly polished parts where a stylus could cause damage or tip-convolution error.
What surface parameters can white light interferometry measure?
It measures surface height, roughness, step height, form, and 3D topography from the interference signal generated during vertical scanning, supporting areal characterization per ISO 25178 workflows.
Why choose white light interferometry over a stylus profilometer?
WLI captures true 3D areal data with nanometer vertical resolution and avoids tip wear and tip-convolution error. Stylus profiling remains useful for simple profile specs and lower-cost routine checks.
White light interferometry (WLI), also known as coherence scanning or vertical scanning interferometry, is a non-contact optical surface metrology technique that measures surface height and topography by analyzing interference between broadband light reflected from a sample and a reference mirror. It produces dense 3D height maps with nanometer-level vertical resolution.
On a CNC cell or metrology bench, the part is placed under an interferometric objective while the optics scan through focus and height. The system records the coherence peak, and software reconstructs the surface from the interference signal. This makes WLI ideal for non-contact inspection of delicate, soft, coated, or highly polished parts that a stylus could damage. Typical applications include tool wear and cutting-edge characterization on inserts and end mills, precision-machined surface finish validation after grinding, fly-cutting, diamond turning, or laser texturing, and depth or step-height checks on micro-features, bores, and optical components. Because WLI captures a dense 3D dataset in one scan, it supports areal surface measurement and better statistical characterization of complex textures and anisotropy under ISO 25178-style workflows. This replaces line-based stylus profiling for many shop-floor quality tasks, giving machinists a fast, damage-free way to verify critical geometry on ultra-precision surfaces.
Saturated detector on polished metals: Polished or coated parts can saturate the detector and destabilize fringe contrast, causing missing data or false height spikes when illumination and objective settings are not tuned to the surface.
Dropouts on steep slopes or deep bores: Steep slopes, deep bores, or shadowed geometries fail to return enough light from oblique or hidden areas. The reconstruction can look complete but is under-sampled, producing unreliable height data.
Method mismatch with tolerance callouts: Using areal WLI where a legacy profile-only stylus parameter or Ra/Rz check is specified can create noncomparable results. Without procedure control, this drives false accept/reject decisions and process escapes.