Influence of Spinel head window thickness on the performance characteristics of a submarine panoramic infrared imaging system

This work explores the influence of head window thickness on the performance of a mid-wave infrared, panoramic periscope imager. Our focus is on transparent spinel ceramic as the head window material. Spinel is an attractive material for IR applications due to its good strength and transmission properties (visible through mid-wave). However, there is some degradation in spinel transmission near the high end of the mid-wave band ( 5μm) as the head window thickness increases. In this work we predict the relationship between head window thickness and imager performance, as quantified by the Noise Equivalent Temperature Difference, and compare these predictions to values estimated from experimental data. We then discuss the implications for imager design and demonstrate a possible approach to correcting for the headwindow-induced losses. The imager used in this study is a compact, catadioptric, camera that provides a 360o horizontal azimuth by -10o to +30o elevation field of view and uses a 2048 x 2048, 15μm pitch InSb detector.