Diffraction control masks known as apodizers are key components required for high contrast imaging and Exoplanet observations. The SBIR firm has taken ultradark carbon nanotube (CNT) coatings from a laboratory curiosity to an enabling technology for stray light control by applying the CNT to apodizers. Delivered prototype components have achieved 1.8E-9 monochromatic contrast in the JPL test bed. The development of apodizer mirrors has required new processes that survive high temperatures and caustic gases including a) low surface figure substrates b) high efficiency reflective coatings c) dark precise CNT growth. Challenges remain, since the ultimate goal is to achieve broad band contrast of 10E-10 for exoplanet coronagraphy envisioned in flagship missions such as LUVOIR. Small flaws in the coating of the apodizers will eventually impact coronagraphy. Current CNT formulations achieve about 0.3% hemispherical reflectance (HR) higher than the 0.1% HR goal. Key goals are to develop a high efficiency reflective coating with minimal inclusions compatible with our substrate and CNT growth process. Secondly, we will decrease the nanotube HR from 0.3% to 0.1% and demonstrate near ideal pseudo-grayscale patterning of nanotubes. Characterization of the apodizers has been performed by measuring witness samples for specular reflection (SR), HR of nanotubes and surface figure. Enhanced characterization will be performed by measuring HR of reflective coatings, SR of the CNT and direct characterization of surface figure. The last two of these are problematic due to the low reflectance of CNTs and the challenge of acquiring figure of apodizers with high density CNT patterning. The final objective is to design methods for enhanced characterization for Phase II and implement a near angle SR capability in Phase I. Phase II will include a characterization capability using high resolution phase mapping to characterize optical density and phase inhomogeneity apodizers. Anticipated
Benefits: Patterned CNT apodizers are enabling technology for high contrast imaging such as required for Exoplanet observations. The technology is also applicable for use on telescopes used in duplex such as Laser Interferometer Space Antenna (LISA), which requires extreme isolation between the transmit laser and the dim received beam. Deep space laser communications will use telescopes in duplex and have to deal with the same type of isolation of the received beam which can be millions of times dimmer than the transmit beam. Apodizers can be used in optical systems operating in high contrast environments such as experienced by autonomous driving systems and military imaging systems. CNT can mitigate stray light in nearly any type of optical instruments. Patterned CNT are being evaluated for use in art and fashion and may be used for high-end watch faces and jewelry.
