In-process chromatic monitoring in the laser cleaning of marble

In-process surface monitoring based on chromatic modulation has been carried out for the laser cleaning of marble, where a sensitive monitoring system is required during cleaning because even a small amount of substrate damage is not permitted when restoring artworks. The chromatic monitoring system described here consists of three photodetectors, fiber optics, a white light source, and a PC-based data acquisition and processing system. This monitor produces measurements that are dependent on the spectral signature of reflected light from the surface. Results show that the spectral parameters derived from the chromatic detection provide not only clear indication of the surface cleanliness and the substrate damage but also useful chromatic information on the surface. The chromatic technique offers unique characteristics such as fast speed, simplicity, and immunity to extraneous influences, which present a reliable monitoring system for laser cleaning processes.