The role of Fe in laser-induced damage in ultrapure KBr

The laser-damage threshold has been measured for several samples of ultrapure KBr crystals. Induced neutron activation analysis and thermal light scattering measurements indicate the major impurity to be Fe 2 + with concentrations in the range .04-.095 ppm and radii in the 17-20 A range. Other impurities either do not contribute to the scattering or are in concentrations 100 ppb or less. The measured damage threshold values were found to have the functional dependence on particle radius and pulse width predicted by the theory of Bennett. 1 Oxygen treatment to the KBr during the crystal growth process is observed to effect the damage threshold values. This suggests a damage mechanism that is related to a species derived from carbon. As an example, carbon present in the sample in ppb concentrations might be converted to CO which is covalently bound to the Fe. In this bound state the Fe no longer contributes to the laser damage.