LASER-CLEANING TECHNIQUES FOR REMOVAL OF SURFACE PARTICULATES

Flash laser heating using short-pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1-mu-m. This is very useful because micron- and submicron-sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser-cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laser irradiation. This permits the effective removal of particles smaller than approximately 20-mu-m, down to as small as 0.1-mu-m, from a solid surface using a modest ultraviolet laser fluence of approximately 0.1 J/cm2.