Application of physical gradient index (Moth-Eye) structures to ALON windows as a durable anti-reflection treatment

Neeta Agarwal; Lee M. Goldman; Suri A. Sastri; Robert J. Ondercin; Paul Kobrin

doi:10.1117/12.820220

27 April 2009 Application of physical gradient index (Moth-Eye) structures to ALON windows as a durable anti-reflection treatment

Neeta Agarwal, Lee M. Goldman, Suri A. Sastri, Robert J. Ondercin, Paul Kobrin

Author Affiliations +

Proceedings Volume 7302, Window and Dome Technologies and Materials XI; 73020K (2009) https://doi.org/10.1117/12.820220
Event: SPIE Defense, Security, and Sensing, 2009, Orlando, Florida, United States

Abstract

The optical performance of windows and domes are subject to degradation from rain and sand erosion damage in harsh flight environments. While durable window and dome materials, such as ALON®, spinel and sapphire are more or less impervious to rain and sand erosion damage in the captive carry environments, the coatings use to provide antireflection (AR) function are not. Rain and/or sand erosion damage of the outer AR coating leads to degradation of the windows optical performance, even when the underlying window itself is not damaged. Surmet has been working on design and development of physical gradient index (Moth- Eye) structures based AR surfaces etched directly into the surface of the ALON substrate. By eliminating the need for less durable coating materials, these structures offer high optical performance without compromising durability. The difficulty of this approach is that the same durability that makes ALON impervious to erosion damage makes it very difficult to etch. Processes have been developed at Surmet which facilitate the etching of fine deep features into ALON surfaces required for broadband AR function. Recent results will be presented.

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Neeta Agarwal, Lee M. Goldman, Suri A. Sastri, Robert J. Ondercin, and Paul Kobrin "Application of physical gradient index (Moth-Eye) structures to ALON windows as a durable anti-reflection treatment", Proc. SPIE 7302, Window and Dome Technologies and Materials XI, 73020K (27 April 2009); https://doi.org/10.1117/12.820220

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KEYWORDS

Etching

Antireflective coatings

Mid-IR

Scanning electron microscopy

Autoregressive models

Gradient-index optics

Optical lithography

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