In the current complex battle field, military platforms are required to operate on land, at sea and in the air in all weather
conditions both day and night. In order to achieve such capabilities, advanced electro-optical systems are being
constantly developed and improved. These systems such as missile seeker heads, reconnaissance and target acquisition
pods and tracking, monitoring and alert systems have external optical components (window or dome) which must remain
operational even at extreme environmental conditions. Depending on the intended use of the system, there are a few
choices of window and dome materials. Amongst the more common materials one can point out sapphire, ZnS,
germanium and silicon. Other materials such as spinel, ALON and yittria may also be considered.
Most infrared materials have high indices of refraction and therefore they reflect a large part of radiation. To minimize
the reflection and increase the transmission, antireflection (AR) coatings are the most common choice. Since these
systems operate at different environments and weather conditions, the coatings must be made durable to withstand these
extreme conditions. In cases where the window or dome is made of relatively soft materials such as multispectral ZnS,
the coating may also serve as protection for the window or dome.
In this work, several antireflection coatings have been designed and manufactured for silicon and multispectral ZnS. The
coating materials were chosen to be either oxides or fluorides which are known to have high durability. Ellipsometry
measurements were used to characterize the optical constants of the thin films. The effects of the deposition conditions
on the optical constants of the deposited thin films and durability of the coatings will be discussed. The coatings were
tested according to MIL-STD-810E and were also subjected to rain erosion tests at the University of Dayton Research
Institute (UDRI) whirling arm apparatus in which one of the coatings showed no rain drop impact damage at all.