Advanced window coatings being developed for drone applications need to be multi-functional. A typical window design includes a hydrophobic outer coating, a solar filter rejecting unwanted spectrum, an EMI layer and/or heater to prevent icing and anti-reflection films. Hydrophobic and hydrophilic thin film materials are available from various vendors. We present our experience in using these materials and their comparative performance with respect to film adhesion and durability. The window can be a common aperture for several different sensors. Adding an EMI shield using a transmitting conducting oxide (TCO) is challenged when visible and NIR transmission is needed. The trade-off between required conductivity and NIR transmission is presented.
Linear variable filters have become a common way to impart wavelength selectivity into optical systems with a minimum of optical elements. Measuring the filter in the presence of steep spectral-spatial gradients is the primary difficulty in characterizing these filters, requiring a small aperture beam resulting in a corresponding loss of signal power. We will discuss our approach to mapping the spectral and spatial distribution of these parts as well as a method to specify these filters. We will also suggest methods to calibrate and align the filters onto a detector, camera or chip.
The effectiveness of infrared imaging sensors for target detection and identification can be greatly enhanced by adding spectral analysis capability. Unfortunately, this usually comes with the penalties of increased size, weight, and significantly increased computational requirements, which limit the rate at which information can be made available to the user. By integrating MEMS, photonics and electronics technologies, a new type of staring spectral imager can be realized. An Adaptive Focal Plane Array (AFPA) device is being developed under DARPA sponsorship that consists of an array of MEMS tunable Fabry-Perot filters, hybridized with a dual band IR focal plane array. The MEMS filters will provide narrowband tuning in the LWIR (8.0-10.7 mm) and simultaneous broadband imaging in the MWIR (3-5 mm). Individual filter elements will be on the size scale of a small number of detector pixels. Each filter will be independently electrically addressable, enabling tailored spectral analysis of different regions in the scene. Rather than collecting the complete hyperspectral cube, work is focusing on methods that will enable selection of spatially optimized spectral band sets for a variety of targets and materials that are selected "on-the-fly" to maximize the contrast between the local background and the target or material to be identified.
This paper discusses the structure and status of the AFPA device and highlights some unique challenges inherent in the integration of MEMS, photonics and electronics technologies.
HfO2/SiO2 polarizer coatings for 1054 nm have been produced that have low stress at explicit environmental conditions without the employment of backside stress- compensation films. In this process hafnia is condensed from a metallic melt and silica from an oxide source, both via electron-beam evaporation. Specifically, this process has been adopted for multilayer designs with stringent requirements on spectral control and wavefront distortion. Efforts to meet these requirements have prompted various investigations of coating stress and spectral behavior, especially under changing environmental conditions. Results have shown that coating stress and optical thickness vary significantly with humidity. THese quantities have been measured under both ambient air and dry nitrogen atmospheres. The effects of coating parameters on stress and environmental stability have been examined for an experimental hafnia/silica polarizer coating. The aforementioned parameters are hafnia deposition rate, oxygen pressure during hafnia deposition, and oxygen pressure during silica deposition. Results indicate a strong correlation of coating stress to oxygen pressure during the silica evaporation. Data on the aging of stress in hafnia/silica coatings will also be presented. The HfO2/SiO2 process has ben utilized in high-laser-damage- threshold coatings for the OMEGA laser system and for National Ignition Facility development coatings at the Laboratory for Laser Energetics.
Conference Committee Involvement (4)
Advances in Thin-Film Coatings for Optical Applications V
11 August 2008 | San Diego, California, United States
Advances in Thin-Film Coatings for Optical Applications III
13 August 2006 | San Diego, California, United States
Advances in Thin-Film Coatings for Optical Applications II
2 August 2005 | San Diego, California, United States
Advances in Thin-Film Coatings for Optical Applications
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