Strengthening of halides for infrared windows

The alkali halides are promising candidates for high-power carbon dioxide laser windows. However, their poor mechanical properties limit their application for windows. In this paper, several methods of strengthening these materials will be discussed. These methods include impurity addition, solid solution formation, use of systems with solid-solid immiscibility gaps and polycrystalline formation. Characterization will include both optical and mechanical properties. The studies indicate that solid solutions (KCl-KBr) can strengthen the halides about twofold without affecting optical properties. An eight-fold increase in hardness has been produced using the NaCl-KCl system but the optical properties are adversely affected. The results of impurity addition (CaCl₂) in KC1 are not clear, but the method does not look promising. Results of polycrystalline formation will also be discussed.