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.

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Plasmonic metasurface coloration has attracted considerable attention in recent years due to its industrial potential. So far, demonstrations have been limited to small patterned areas fabricated using expensive techniques with limited scalability. This study elevates the technology beyond the common size and volume limitations of nanofabrication and demonstrates aluminum‐coated polymer‐based colored metasurfaces of square‐centimeter size by embossing, injection molding, roll‐to‐roll printing, and film insert molding. Different techniques are compared and the requirements and bottlenecks in terms of master fabrication, replication, metallization, and protection coating for large‐scale production of sub‐wavelength metasurfaces are discussed. Most notably, it is demonstrated that plasmonic metasurface colors are compatible with film insert molding. The results indicate a promising future for plasmonic colors as a viable alternative for decorating mass‐produced polymer parts.

Ultra-low power electrically reconfigurable magnetoelectric microwave devices J. Appl. Phys. 112, 073915 (2012) Broadband and ultrathin screen with magnetic substrate for microwave reflectivity reduction Appl. Phys. Lett. 101, 154101 (2012) Tunable, narrow-band, all-metallic microwave absorber Appl. Phys. Lett. 101, 141115 (2012) Insertable system for fast turnaround time microwave experiments in a dilution refrigerator Rev. Sci. Instrum. 83, 093904 (2012) Coherent terahertz radiation from high-harmonic component of modulated free-electron beam in a tapered twoasymmetric grating structure Appl. Phys. Lett. 101, 123503 (2012) Additional information on J. Appl. Phys. We analyze ultra strong non-resonant field enhancement of THz field in periodic arrays of nanoslits cut in ultrathin metal films. The main feature of our approach is that the slit size and metal film thickness are several orders of magnitude smaller than the wavelength k of the impinging radiation. Two regimes of operation are found. First, when the grating period P ( k, frequency-independent enhancement is observed, accompanied by a very high transmission approaching unity. With high accuracy, this enhancement equals the ratio of P to the slit width w. Second, when the grating period approaches the THz wavelength but before entering the Raleigh-Wood anomaly, the field enhancement in nanoslit stays close to that in a single isolated slit, i.e., the well-known inversefrequency dependence. Both regimes are non-resonant and thus extremely broadband for P < k. The results are obtained by the microscopic Drude-Lorentz model taking into account retardation processes in the metal film and validated by the finite difference frequency domain method. We expect sensor and modulation applications of the predicted giant broadband field enhancement.

We report on the observation of ultrafast impact ionization and carrier generation in high resistivity silicon induced by intense subpicosecond terahertz transients. Local terahertz peak electric fields of several MV cm −1 are obtained by field enhancement in the near field of a resonant metallic antenna array. The carrier multiplication is probed by the frequency shift of the resonance of the antenna array due to the change of the local refractive index of the substrate. Experimental results and simulations show that the carrier density in silicon increases by over seven orders of magnitude in the presence of an intense terahertz field. The enhancement of the resonance shift for illumination from the substrate side in comparison to illumination from the antenna side is consistent with our prediction that the back illumination is highly beneficial for a wide range of nonlinear processes.

In this paper we analyze the theoretical limits of a metamaterial converter that allows for linear-toelliptical polarization transformation with any desired ellipticity and ellipse orientation. We employ the transmission line approach providing a needed level of the design generalization. Our analysis reveals that the maximal conversion efficiency for transmission through a single metamaterial layer is 50%, while the realistic reflection configuration can give the conversion efficiency up to 90%. We show that a double layer transmission converter and a single layer with a ground plane can have 100% polarization conversion efficiency. We tested our conclusions numerically reaching the designated limits of efficiency using a simple metamaterial design. Our general analysis provides useful guidelines for the metamaterial polarization converter design for virtually any frequency range of the electromagnetic waves.

Chalcogenide glasses are receiving a lot of attention due to their unique optical properties. In this paper we study the optical properties of As2S3 and GaLaS glasses in a broad terahertz (THz) frequency range (0.2-18 THz). Complex dispersion behavior with drastic changes of refractive index and absorption coefficient is found for both glasses. We observe the breakdown of the universal power-law dependence of the absorption coefficient due to atomic vibrations observed at low THz frequencies in disordered materials, and see the transition to localized vibrational dynamics for the As2S3 compound at higher frequencies. In addition, As2S3 displays two transparency regions, at 7-8 THz and 12.2 THz, of potential interest for future nonlinear applications in the THz range.