Fabrication and testing of plasmonic optimized transmission and reflection coatings

We designed, fabricated, and tested surface-plasmon-based transmissive coatings in the MWIR (mid wave infrared) and LWIR (long wave infrared). This method offers certain advantages over current coatings technologies such as thin-film stacks and two-dimensional surface structuring (e.g. motheyes) while exploring an entirely different physical mechanism for achieving transmission. Thin-film stack technology relies on interference between layers of the stack, and often many layers are required for high efficiency performance. Two-dimensional surface structuring can optimize transmission over a broad spectral and angular domain1. Here the physical mechanism is an effective index matching between air and the substrate due to subwavelength surface features, such as tall pyramids. These pyramids must have a high-aspect ratio, resulting in a surface of many tall thin features, which may not be mechanically robust. In this work, we created a transmissive surface out of a metal skin perforated with an array of subwavelength apertures. The surface is the infrared analog of a frequency selective surface (FSS) common in the microwave regime. Such perforated metal surfaces are predicted to have nearly 100% transmission over selected wavelength and angular ranges. These ranges are determined by array geometry, period, and aperture size and shape, allowing the designer considerable freedom. Array geometry and aperture shape were investigated for tailoring spectral features.