In order to use infrared windows in the electro-optical systems, which are integrated to the air platforms, its strength and
durability should be high enough for harsh environmental conditions. One of the most challenging environmental
conditions is the rain erosion. An infrared substrate may not continue its necessary functions at high velocity flight under
rain. Special coating techniques should be used for the infrared transparent substrate to increase its durability.
In this study, development of the hard carbon coating, whose substrate material is Germanium, will be discussed. Finite
element analysis of the substrate material will be compared with the rain erosion test data. Test results for the developed
coating will also be presented to show the improvement on durability performance.