Line confocal imaging (LCI) is a unique optical technology for metrology requiring resolutions down to 50 nm. In the past, confocal technology was limited to single point or multipoint sensors based on a coaxial design. With LCI, a major breakthrough is achieved using a novel off-axis confocal design that offers a line scan capability with numerous benefits over the traditional coaxial approach. In this two part blog post, we examine the advantages of line confocal sensors over traditional point-based solutions.
In the off-axis design of line confocal sensors, the optical assembly separates the projected light into wavelengths and focuses a horizontal line of each color at a different distance from the sensor, forming a focal plane.
What makes 3D line confocal sensors unique?
The key advantage of line confocal sensors is their ability to generate 3D topography (3D surface geometry), 3D tomography (multi-layer 3D geometry and 2D intensity), and 2D intensity data simultaneously over a 2k line scan at fast scan rates (e. g., 3 kHz). Confocal scanning avoids unwanted reflections from shiny metal surfaces and the off-axis arrangement is what permits multi-layer (tomography) scanning.
In addition, confocal sensors are much easier to mount to acquire high quality scan data with angular performance of +/- 20 degrees on mirror like surfaces, and +/- 80 degrees on opaque, matte surfaces. Excellent angular performance makes line confocal sensors less sensitive to surface orientation when acquiring scan data, and line confocal scanning can handle just about any surface—from transparent, mirror-like to opaque and shiny. Before line confocal was possible, single or multiple point coaxial confocal systems were the standard, but required long scanning acquisition to generate a profile or area and were limited to measuring the top surface only.