Down to the nano-scale: confocal sensors measure texture and surface finish of laser-machined components

摘要

The latest confocal chromatic sensors offer extremely high sensitivity and sub-micrometre resolution, providing significant advantages when it comes to inspecting the shape, size and surface topography of MEMS structures during or post-production. These sensors can be integrated to linear X-Y stages, machine tools or special purpose inspection systems with closed loop feedback control. The confocal chromatic measuring principle works by focusing polychromatic white light onto the target surface using a multi-lens optical system. The lenses are arranged in such a way that the white light is dispersed into a monochromatic light by controlled chromatic deviation (aberration). A certain deviation (specific distance) is assigned to each wavelength by a factory calibration. Only the wavelength that is exactly focussed on the target surface or material is used for the measurement. This light reflected from the target surface is passed through a confocal aperture onto a spectrometer, which detects and processes the spectral changes.