Optical solar reflector smart radiators are able to control the temperature of spacecraft. This work demonstrates a novel smart optical solar reflector using a patterned thermo-chromic VO2 plasmonic meta-surface design. The VO2 meta-surface combines the temperature induced phase transition of VO2 with plasmonic resonances resulting in a significant enhancement of the infrared absorption. The enhanced absorption obtained at a reduced VO2 coverage results in superior emittance tunability Δε and lower solar absorptance α compared to a corresponding thin-film reflector. An emittance tunability of 0.48 is obtained for the meta-reflector design, representing a 30% improvement compared to the unstructured film. Meta-surface based smart optical solar reflectors offer a new route toward energyefficient and cost-effective passive thermal control systems of spacecraft and other surfaces.

Optical Solar Reflectors are devices that combine high reflection for visible wavelengths with a strong emissivity in the infrared. Compared to the conventional rigid quartz tiles used on spacecraft since the 1960s, thin-film solutions can offer a significant advantage in weight, assembly and launch costs. Here, we present a metasurface based approach using an Al-doped * To whom correspondence should be addressed † Electronics ‡ Physics ¶ CREO § NILT ZnO (AZO) transparent conducting oxide as infrared plasmonic material. The AZO is patterned into a metasurface to achieve broad plasmonic resonances with enhanced absorption of electromagnetic radiation in the thermal infrared. In the visible range, the transparent conducting oxide provides low losses for solar radiation, while intrinsic absorption losses in the ultraviolet range are effectively suppressed using a multilayer reflecting coating. The addition of high-emissivity layers to the stack eventually results in comparable emissivity values to the thin plasmonic device, thus defining a window of opportunity for plasmonic absorption as a design strategy for ultrathin devices. The optimized experimental structure achieves solar absorptance (α) of 0.16 and thermal emissivity (ε) of 0.79. Our first prototype demonstrator paves the way for further improvement and large-area fabrication of metasurface solar reflectors, and ultimately their application in space missions.

The interest in plasmonic electro-optical modulators with nanoscale footprint and ultrafast low-energy performance has generated a demand for precise multiphysics modeling of the electrical and optical properties of plasmonic nanostructures. We perform combined simulations that account for the interaction of highly confined nearfields with charge accumulation and depletion on the nanoscale. Validation of our numerical model is done by comparison to a recently published reflective meta-absorber. The simulations show excellent agreement to the experimental mid-infrared data. We then use our model to propose electro-optical modulation of the extinction cross-section of a gold dimer nanoantenna at the telecom wavelength of 1550 nm. An ITO gap-loaded nanoantenna structure allows us to achieve a normalized modulation of 45% at 1550 nm, where the gap-load design circumvents resonance pinning of the structure. Resonance pinning limits the performance of simplistic designs such as a uniform coating of the nanoantenna with a sheet of indium tin oxide, which we also present for comparison. This large value is reached by a reduction of the capacitive coupling of the antenna arms, which breaks the necessity of a large volume overlap between the charge distribution and the optical nearfield. A parameter exploration shows a weak reliance on the exact device dimensions, as long as strong coupling inside the antenna gap is ensured. These results open the way for a new method in electro-optical tuning of plasmonic structures and can readily be adapted to plasmonic waveguides, metasurfaces and other electro-optical modulators.

A soft xray multilayer mirror scanning monochromator for magnetically confined fusion plasmas Rev.A simple two-min'or monochromator based on multilayer films has been developed as a part of a refiectometer under construction at the University of Wisconsin Synchrotron Radiation Center. Measurements of the perfonnance of this monochromator and the characterization ofa typical component mirror have been made. At AIKa the monochromator has a peak transmission of9%, which is 55% of the theoretical value. Its resolution,), I b.A., is 35.

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A simple two -mirror monochromator based on multilayer films has been developed for use with synchrotron radiation.Measurements of the performance of this monochromator and the characterization of a typical component mirror are described.

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