Calibration of a Chromatic Confocal Microscope for Measuring a Colored Specimen

In this paper, a color correction method is proposed to improve measurement accuracy for chromatic confocal microscopy (CCM) when measuring a colored specimen. Characteristic curve shifting due to selective reflection from color surfaces was analyzed based on a laboratory CCM system developed by the authors' team. Theoretically, when the color of the targeted surface is different from that represented by the central wavelength of the light source, the characteristic curve of CCM would have a notable deviation from that of an achromatic surface. In this study, this conclusion was verified through both simulation and experiments. Using a set of standard color calibration pieces, a color correction method was proposed accordingly to quantify the characteristic curve shifting. To validate the proposed method, a laser scanning confocal microscope Carl Zeiss LSM700 was used as the referencing system. Experimental data showed that with the color correction method, measurement errors can be controlled within 10 nm. Compared with the measurement without color correction, the measurement accuracy is significantly improved.