A modified chromatic confocal system for spectral reflectance measurement

Abstract

Spectral reflectance plays an important role in the evaluation of the object surface, such as the color, the roughness. A new method is proposed to measure the spectral reflectance at a fixed incident angle. The chromatic confocal displacement sensor is modified with an annular stop to generate a hollow cone beam of incident light on the to-be measured sample surface. With self-reference strategy, the upper and lower envelops are derived from the axial scanning of the dispersion probe, whose minus is named as self-reference spectrum. Thus, the reflectance at every wavelength among the valid dispersion bandwidth can be achieved by comparing the self-reference spectra of the sample surface and a standard mirror with known spectral reflectance. With the proposed method and experimental setup, the spectral reflectance of several metal surfaces is obtained and compared with their theoretical spectral reflectance within ±0.04. It proves that the modified chromatic confocal can provide feasible results for the spectral reflectance measurement.