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Optical damage at the part per million level: the role of trace contamination in laser-induced optical damage

Although sealed, Q-switched Nd:YAG lasers are carefully designed to ensure that the laser intensities in the optical train are well below the intrinsic damage threshold of all components, optical damage remains a frequently encountered long term failure mode. It has been found that during continuous elevated temperature operation (greater than approximately equals 50 degree(s)C), optical damage can occur in a matter of hours. Using a recently developed technique, we have shown that most (if not all) of this damage is due to trace contamination from a variety of sources. In a pure nitrogen environment, even the levels of contamination typical in the output of ultrahigh purity gas bottles is sufficient to induced damage at temperatures greater than approximately equals 60 degree(s)C. This paper describes a method which may be used to identify the types of contaminants most likely to induced optical damage and the levels of contamination at which damage may occur. The application of this method may be extended to provide a broad data base for the use by laser designers in selecting materials and by future researchers in identifying the root causes of contamination-induced damage mechanisms.