Molecular — impurity absorption in KC1 for infrared laser windows

Abstract

Residual impurity absorption in the 10µm region severely limits the usefulness of KCl as a high-power CO2 laser window. In order to investigate possible origins for this absorption, KCl was doped with carbonate and hydroxyl impurities, and grown in various atmospheres. Characteristic absorption bands in the infrared and ultraviolet were used to determine relative dopant concentrations. Growth conditions introducing CO/ 3 = exclusively, led to relatively low and featureless absorption spectra in the 10.6µm region, while conditions introducing both CO/ 3 = and OH− led to enhanced absorption. (Additionally, a correlation is indicated between the strength of absorption at 10.6µm and that of the oxygen band at 0.26µm in samples grown in atmospheres in which oxygen was present). Our observations suggest the possibility of absorption due to CO/ 3 ≽ complexes, NO 3 − , HCO 3 − and/or ClO 3 − in the 10µm region. While the effects of ultralow concentration of these impurities remain uncertain, the present results suggest that their presence may well contribute to extrinsic absorption in the 10µm region.