Sample: A polka dot beam splitter (Thorlabs’ BPD254-FS) consists of 100 µm large metallic squares on top of a glass substrate.
lineWLI technology measures the profile of one line in one shot. Each line consists of over 1,500 independent measurement points. The sensor measures the surface height for each point. The technology works on the highly reflective metal coating just as well as on the bare glass substrate:
Here are 2 surface profiles along the X direction across the mirrors and the substrate:
lineWLI technology does not need special vibration isolation to achieve sub-nanometer resolution.