Nanostructured antireflection coating technology for enhanced MWIR and LWIR band sensing performance

Nanostructured antireflection (AR) coatings reducing optical reflections and maximizing radiation transmitted onto the surfaces of substrates, optics and optical devices such as detectors have many potential optical applications over ultraviolet (UV) to infrared (IR) wavebands including for NASA sensor applications. Through nanoengineering optical layers and tuning their refractive indexes, broadband and omnidirectional suppression of light reflection and scattering is achievable with increased optical transmission for enhanced IR detector and system performance over a wide range of light incidence angles. AR nanostructures have been developed that enable the realization of optimal AR coatings with high laser damage thresholds and high reliability in extreme low temperature environments and under launch conditions. These advanced nanostructured AR coatings we have developed and tested on GaSb and IR detector arrays devices primarily for 3-5 and 8-14 µm MWIR/LWIR applications provide substantial improvements over more conventional thin film AR coating technologies such as quarter-wavelength coatings. The growth of step-graded nanostructured layers using a process involving deposition at different tilt angles has produced single-layer AR coatings utilizing ZnS demonstrating below 4% reflectance, compared to ~34% reflectance for uncoated GaSb, across LWIR bands of interest with substantial improvement in quantum efficiency. In this paper we review and present latest developments and testing results for these high-performance nanostructure-based AR coatings for advanced LWIR band NASA Earth Science sensing and imaging applications.