Kaikai Du

Control over emissivity of zero-static-power thermal emitters based on phase-changing material GST

A switchable, tunable and wavelength-selective thermal emitter is experimentally demonstrated with simple layered structures by controlling the phases of Ge<inf>2</inf>Sb<inf>2</inf>Te<inf>5</inf>, achieving a high emission extinction ratio of 11dB.

Wavelength and Thermal Distribution Selectable Microbolometers Based on Metamaterial Absorbers

An uncooled microbolometer based on metamaterial absorbers is investigated. The absorption peak reaches 90%, and the peak wavelength can be tailored from 2.4 to 10.2 μm with corresponding bandwidth varying from 0.5 to 1.5 μm by tuning the geometric parameters of the absorbers, covering two atmosphere windows (3-5 μm and 8-14 μm). The thermal distribution in the microbolometer can be adjusted to realize a strong thermal response. In the given situation with a pixel size of 25.07 μm, the temperature response of the detector reaches 1.3 K. The microbolometer can be potentially used in thermal imaging at selected wavelengths in the mid-infrared and far-infrared regimes.

Broadband optical absorption based on single-sized metal-dielectric-metal plasmonic nanostructures with high-ε″ metals

We propose a broadband, efficient, ultra-thin metal-insulator-metal (MIM) absorber with a simple single-sized disk configuration by utilizing metals with high imaginary part of permittivity (e″). The physics behind this is that field dissipation is remarkably enhanced in MIM absorbers with high-e″ metals, significantly extending the absorption bandwidths, which are conventionally limited by magnetic resonances of MIM absorbers with low-e″ metals. The experimentally demonstrated MIM absorber based on tungsten with high-e″ yields broadband absorption from visible to near-infrared range (400–1700 nm) with an average measured absorption of 84%. The ultra-thin and single-sized nanostructure with broadband efficient absorption facilitates the scalability to large-area photonic applications.

Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting

A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

Thermal camouflage based on the phase-changing material GST

Camouflage technology has attracted growing interest for many thermal applications. Previous experimental demonstrations of thermal camouflage technology have not adequately explored the ability to continuously camouflage objects either at varying background temperatures or for wide observation angles. In this study, a thermal camouflage device incorporating the phase-changing material Ge2Sb2Te5 (GST) is experimentally demonstrated. It has been shown that near-perfect thermal camouflage can be continuously achieved for background temperatures ranging from 30 °C to 50 °C by tuning the emissivity of the device, which is attained by controlling the GST phase change. The thermal camouflage is robust when the observation angle is changed from 0° to 60°. This demonstration paves the way toward dynamic thermal emission control both within the scientific field and for practical applications in thermal information.Thermal camouflage: hidden in hot or coldThermal camouflage surfaces developed by Chinese researchers can be tailored to hide objects in front of different backgrounds. Traditional thermal camouflage comprises low-emissivity cloaks that lower the apparent temperature of vehicles or people to match their surroundings; however, objects can only be well-hidden when the background is one particular temperature. Qiang Li and co-workers at Zhejiang University in Hangzhou deposited a germanium-antimony-tellurium alloy onto gold film, before thermally annealing their samples at 200 °C. By varying the annealing time, the researchers prepared samples that were completely amorphous (randomly structured), completely crystalline (ordered), or intermediate states between the two. They found that the more crystalline samples had higher apparent temperatures, meaning the surfaces could be tailored to work at a range of background temperature. As well as benefitting military, such technology could allow better heat management during space travel.

Chip-Scale Plasmonic Sum Frequency Generation

Plasmonics provides a promising candidate for nonlinear optical interactions because of its ability to enable extreme light concentration at the nanoscale. We demonstrate on-chip plasmonic sum frequency generation (SFG) with a metal—dielectric–metal nanostructure. The two cross-polarized pumps (800 and 1500 nm) are designed to match the two resonances of this plasmonic nanostructure to make the most of the electric field enhancement and spatial overlapping of the modes. Since these two resonances are predominantly determined by the sizes of the top metallic nanostructures in the same direction, the SFG (521 nm) can be independently controlled by each pump via changing these sizes. This study exerts the full strength of plasmonic resonance induced field enhancement, thereby paving a way toward using nanoplasmonics for future nonlinear nanophotonics applications, such as optical information processing, imaging, and spectroscopy.