Characterizing laser conditioning of carbon contamination of optics using surface temperature and photo thermal common-path interferometry

High reflectivity distributed Bragg reflectors contaminated with carbon micro particles were tested with a high power 1070nm continuous wave laser. Thermal camera images of the samples showed a consistent reduction in surface heating for samples that had prior exposure to the same irradiance. To characterize irradiance vs. conditioning, the absorption change of samples was measured using photo thermal common-path interferometry before and after laser exposure. Absorption was reduced from 10% at 13kWcm-2 to up to 60% at 24kWcm-2 Surface microscope images showed particle change beginning at low irradiances with particles fragmenting, reducing in size, and being removed. Higher irradiances caused a permanent change in the substrate in the area of the original particle.