Chromatic confocal setup for displacement measurement using a supercontinuum light source

Abstract

Chromatic confocal microscopy is a technique to measure distances by analyzing the spectrum of the light reflected by a sample. The key element of the confocal setup is a dispersive lens, which focuses different wavelengths at different distances from the lens. In this paper, a novel setup realized with a supercontinuum light source and a spatial filter composed by reflective elements is described. The supercontinuum source is implemented by injecting high power pulses from a microchip laser into a Ge-doped microstructured optical fiber. The usage of metallic parabolic mirrors, for the focusing and collimation required in the spatial filter, lets the dispersive lens be the only dispersive element of the confocal setup and improves the efficiency of the spatial filter itself. A silicon-based spectrometer is used for the acquisition of the spectra, which are normalized and Gaussian-fitted before extracting the displacement information. A complete calibration is performed, and the set of wavelengths from 500nm to 900nm can be mapped into a 280μm measuring range. The obtained relative accuracy of 0.36% shows an enhancement of almost one order of magnitude when compared to other supercontinuum-based confocal systems.