1. Why use white light interferometry?
WLI 3D microscope provides:
- area topography, including shaping, waviness and roughness
2. Interference objectives
2.1 Michelson (1.5x ~ 5x)
- low magnification
- large field of view
2.2 Mirau (10x ~ 100x)
- medium to high magnification
- medium to small field of view
2.3 Linnik (any magnification)
3. Measurement modes
3.1 Phase shift interferometry
- Used for testing smooth objects with very high precision (0.1 nm)
3.2 White light interferometry
- True 3D measurement of surface area.
- Ability to measure rough surfaces.
- Good results with low contrast fringes.
- Results independent of intensity variations across field of view.
- Vertical height limited only by scanner and objective working distance.
- No step height ambiguities.
|White light interferometry||Phase shifting interferometry|
|Vertical resolution ~3 nm||Vertical resolution < 0.1 nm|
|Steps or surface variations up to 10 mm||Smoothly varying surfaces|
|Surfaces with rough/steep surfaces||Polished materials, small height differences|
4. Some notes
"Surface roughness", Ra (Sa) is the average of the absolute value of profile heights over a given length (area).
ASME B46.1-2019: Surface Texture (Roughness, Waviness, Lay)
The Root Mean Square roughness (Rq) is the root mean square average of the roughness profile ordinates.
Ra is the arithmetic average of the absolute values of the profile height deviations from the mean line, recorded within the evaluation length.