Experiments on laser cleaning of sooted optical windows.

To develop laser-ignition technology, transparent glass plates were artificially sooted and irradiated repetitively by laser from the front (sooted) and back sides separately. Generally, the back-side irradiation was more effective at soot removal. However, the cleaning effect was saturated after thousands of laser shots. Although the saturated soot quantity was a decreasing function of the laser fluence per pulse, its magnitude remained the same for both front-side and back-side irradiations. In examining several soot-removal mechanisms proposed so far, it was found that the aerodynamic force produced by the flow induced by the laser heating of the soot was the most plausible mechanism.