Threshold measurements in laser-assisted particle removal

摘要

Laser assisted particle removal (LAPR) is a novel technique capable of removing particulate contamination from solid surfaces. LAPR uses an energy transfer medium which preferentially absorbs into capillary spaces under and around the particles on the contaminated substrate. Laser irradiation causes explosive evaporation of the energy transfer medium via absorption into the energy transfer medium itself or the substrate/particle system with subsequent conductive heat transfer. The explosive force propels particles off the substrate much like a small rocket engine. In our experiments, LAPR was used to remove 9.5 $mu@m Al$-2$/O$-3$/, 5 $mu@m Al$-2$/O$-3$/, and 1 $mu@m polystyrene particles from Si surfaces at the wavelengths of 10.6 $mu@m and 9.6 $mu@m using water as the energy transfer medium. At these wavelengths the laser energy is absorbed predominantly in the water. Laser removal thresholds (J/cm$+2$/) were obtained using a degenerate threshold model. The temperature rise in the energy transfer medium was estimated, suggesting that superheating of the absorbed water is a reasonable mechanism for LAPR.