15 October 2004 Cleaning optical surfaces from the inside out
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Abstract
The advantages of backside irradiation and controlling the polarization and angle of incidence of laser beams used to conventionally clean surfaces have been described previously. This paper considers beams internally incident upon the surface of a transparent substrate at angles of incidence beyond the critical angle for total internal reflection. Attenuated total internal reflection provides an efficient means for both finding and removing absorbing contaminants. Beams may enter the substrate through an edge or a coupling prism. Erbium laser pulses were used to remove water from several dielectric and semiconductor materials. In some cases the water was explosively removed, with no sign of damage to the substrate. A 2.94 μm laser should be especially effective whenever water is present, either naturally from adsorption or capillary condensation or when added for steam laser cleaning. Unabsorbed light can be efficiently routed to clean adjacent areas through multiple total internal reflections. Thus some of the scanning is done at the speed of light. Theory indicates that ATR laser cleaning is effective for very small particles that cannot be removed by shock laser cleaning. This paper will describe attenuated total internal reflection laser cleaning and compare it to conventional laser cleaning techniques.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
George Dube, Arthur J. Braundmeier, J. Daniel Kelley, "Cleaning optical surfaces from the inside out", Proc. SPIE 5526, Optical Systems Degradation, Contamination, and Stray Light: Effects, Measurements, and Control, (15 October 2004); doi: 10.1117/12.555417; https://doi.org/10.1117/12.555417
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