Optical Metrology Calibration Limits for Micro Machined Aluminum Components
Optical metrology of micro-machined aluminum requires phase-filtering algorithms, reflection polarization, and exact 20°C thermal drift corrections.
White Light Interferometry
Meaning
Non-destructive optical technique using broadband light to measure surface profiles provides a way to characterize the roughness and height of precision parts. Interference occurs when the path length of the light reflected from a sample matches the path length of a reference beam. Because white light has a short coherence length, the interference fringes only appear when the distances are nearly identical.
This technique stops applying on surfaces that absorb all incident light or on materials with extreme porosity.
Interference Geometry
Optical systems typically use a Mirau or Michelson objective lens to split and recombine the light. The sample is moved vertically while a camera records the changes in light intensity at every pixel. This data is used to build a three-dimensional map of the surface.
Profile Reconstruction
Software identifies the position of the highest contrast fringe to determine the exact height of each point. This method provides better vertical resolution than standard microscopy. It is used to measure the depth of etched channels in microfluidic devices.
Metrological Integrity
Results are highly repeatable and can be compared against physical standards. White light interferometry is preferred for applications where contact probes would scratch the surface. It ensures that the manufacturing process remains within the required tolerances for high-performance optics.