Simultaneous local spectral, colorimetric, and topographic characterization of laser-induced colored stainless steel with low coherence interference microscopy

Laser marking is a well-established advanced technology for changing the color properties of an object. The spectral response or color information induced by the laser is generally measured with a spectrometer or an ellipsometer. These instruments only provide an average response over an area of a few thousand mu m2 at best. However, color laser marking is a local process that modifies the structure of the metal at a micrometer scale. In this work, we propose a technique for extracting simultaneously the 3D topography and the 2D spectral re-sponse from 460 nm to 900 nm, providing color information over this spectral range, in a single measurement. The proposed technique uses a low-coherence interference microscope to provide a laterally diffraction-limited measurement ( similar to 1 mu m) over a large field of view (up to 200 x 200 mu m2) with the advantages of being rapid < 3 min) and contactless. Through the Fourier Transform analysis of the measured interferogram, a multimodal characterization (quantitative spectra, color (xy) and topography) of reflective samples can be achieved. Results obtained on laser-induced colored stainless steel are reported.