Optical Profilometry

Optical Profilometry

Mid-Range Optical Profilometry: An Overview

Profilometry for surface characterization and dimensioning is a key area of expertise for Covalent Metrology and is proving invaluable to customers across a wide range of applications. At Covalent Metrology, profilometry covers a complete range of surface features using everything from atomic force microscopy (AFM) to optical systems to mechanical stylus systems. The purpose of this paper is to discuss the technology behind each of the three optical profilometry techniques Covalent Metrology offers and to discuss the relative advantages of each of them.

Laser Confocal Microscopy

This microscope combines white light with a laser light source to scan a part’s surface and collect an optical image and high-resolution surface data. The instrument collects the reflected laser light and analyses its intensity (variable due to interference patterns within the beam) relative to the z-position of the laser to determine nanometer-level heights of features on the sample’s surface.

Industries:

Medical devices, quality control, mechanical parts, machined parts, polished parts, injected parts, sintered parts, multimaterial parts.

Measurements:

  • Dimensions (distances, heights, widths) on parts up to 200mm x 100mm (height resolution <1µm, width repeatability 1µm)
  • Flatness
  • Angles
  • Curvatures
  • Profile slices

Example Outputs

Laser Confocal Microscopy

Laser Confocal Microscopy

Patterened Light/ Wide Area 3d Measurement

Covalent uses an optical instrument to measure larger samples: the Wide Area 3D instrument projects patterned light on the surface of the part to measure and identifies the distortions created by the surface.
Measurements are made with high resolution (height resolution <1µm, width repeatability 1µm) on large, inch-scale, areas within minutes, while traditional CMM is a longer process. This technique is non destructive and minimizes the risk of damaging the part in its processing, since no probe is put in contact with the part.
A 3D model of the surface is created and can be analyzed for dimensions, angles, curvature along specific lines, as well as for flatness.

Industries:

Medical devices, electronic components and assemblies, quality control, mechanical parts, machined parts, injected parts, multimaterial parts.

Measurements:

  • Dimensions (distances, heights, widths) on parts up to 200mm x 100mm (height resolution <1µm, width repeatability 1µm)
  • Flatness
  • Angles
  • Curvatures
  • Profile slices

Example Outputs

Stick of RAM (Patterned Light/ Wide Area Measurement) approximately 15cm long

5-Cent coin 3D measurement (Patterned Light/ 3D Wide Area Measurement)

White Light Interferometry

White light interferometry (WLI), a type of coherence scanning interferometry, a class of optical surface measurement methods using the localization of interference fringes during a scan of optical path length as a means to determine surface characteristics such as topography, transparent film structure, and optical properties. WLI is currently the most common interference microscopy technique for areal surface topography measurement by utilizing spectral broadband, white light to achieve interference fringe localization.

Industries:

Optical components, tribology, surface quality control, solar, medical devices.

Measurements:

  • 2D/3D surface mapping
  • Step height
  • Radius of curvature of optical surface or other surfaces
  • Profile slices
  • Slope analysis
  • Power spectral density (PSD) views
  • Built in SPC (pass/fail indicators) with automated region analysis to separate height, intensity, masking

Example Outputs

Penny 3D measurement (White Light Interferometry): barely visible with the naked eye, the figure of Lincoln sitting in the monument is scanned in detail. 

Feature on a circuit board (White Light Interferometry)