|Date||March 2, 2018||Time||3:35 - 5:00 pm|
|Location||Baylor Sciences Building, Room E.125|
Large Optical Nonlinearity of Nanoantennas Coupled to an Epsilon-Near-Zero Material
The size and operating energy of a nonlinear optical device are fundamentally constrained by the weak nonlinear optical response of common materials. Here, we report that a 50-nm-thick antenna based optical metasurface fabricated on epsilon-near-zero substrate could exhibit broadband (∼ 400 nm bandwidth) and ultrafast (recovery time less than 1 ps) intensity-dependent refractive index n2 as large as − 3.73 ± 0.56 cm2 GW−1 (n2 value of glass is (2.5 ± 1.2) × 10−7 cm2GW−1). Furthermore, the metasurface exhibits a maximum optically induced refractive index change of ± 2.5 over a spectral range of ∼ 200 nm. The inclusion of low-Q nanoantennas on an epsilon-near zero thin film not only allows the design of a metasurface with an unprecedentedly large nonlinear optical response, but also offers the flexibility to tailor the sign of the response. This technique removes a longstanding obstacle in nonlinear optics: the lack of materials with an ultrafast nonlinear contribution to refractive index on the order of unity. It consequently offers the possibility to design low-power nonlinear nano-optical devices with orders-of-magnitude smaller footprints.
Reference: M. Zahirul Alam 1, Sebastian A. Schulz 1,2,3, Jeremy Upham1, Israel De Leon 4* and Robert W. Boyd1,5 Large optical nonlinearity of nanoantennas coupled to an epsilon-near-zero material Nature Photonics volume 12, pages 79, 83 (2018)
Resonant Thermoelectric Nanophotonics
Photodetectors are generally based either on photocurrent generation from electron–hole pairs in semiconductor structures or on radiation energy of wavelengths usually in IR range that are below bandgap absorption. For both, resonant plasmonic and nanophotonic structures have been successfully used to enhance performance. Here, we show subwavelength thermoelectric nanostructures designed for resonant spectrally selective absorption, which creates large localized temperature gradients even with unfocused, spatially uniform illumination to generate a thermoelectric voltage. We show that such structures are tunable and are capable of wavelength-specific detection, with an input power responsivity of up to 38 V W–1 , referenced to incident illumination, and bandwidth of nearly 3 kHz. This was obtained by combining resonant absorption and thermoelectric junctions within a single suspended membrane nanostructure, yielding a bandgap-independent photodetection mechanism. We report results for both bismuth telluride/antimony telluride and chromel/alumel structures as examples of a potentially broader class of resonant nanophotonic thermoelectric materials for optoelectronic applications such as non-bandgap-limited hyperspectral and broadband photodetectors.
Reference: Kelly W. Mauser, Seyoon Kim, Slobodan Mitrovic, Dagny Fleischman, Ragip Pala, K. C. Schwab, Harry A. Atwater. “Resonant Thermoelectric Nanophotonics.” Nature Nanotechnology 12, 770-775 (2017).
|Publisher||Department of Physics|
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