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Light-Induced Pulling and Pushing by the Synergic Effect of Optical Force and Photophoretic Force

Optical force, coming from momentum exchange during light-matter interactions, has been widely utilized to manipulate microscopic objects, though mostly in vacuum or in liquids. By contrast, due to the light-induced thermal effect, photophoretic force provides an alternative and effective way to transport light-absorbing particles in ambient gases. However, in most cases these forces work independently. Here, by employing the synergy of optical force and photophoretic force, we propose and experimentally demonstrate a configuration which can drive a micron-size metallic plate moving back and forth on a tapered fiber with supercontinuum light in ambient air. Optical pulling and oscillation of the metallic plate are experimentally realized. The results might open exhilarating possibilities in applications of optical driving and energy conversion.
Physical Review Letters, Vol.118, Issue 4, pp.043601 (2017)
Editors' Suggestion, Cover Paper, Featured in APS Physics

Narrowband Absorbers: Spatially and Spectrally Resolved Narrowband Optical Absorber Based on 2D Grating Nanostructures on Metallic Films
Two spatially and spectrally resolved narrowband absorbers based on 2D grating nanostructures (polymethylmethacrylate (PMMA) grating and gold grating) on metallic films are designed, fabricated, and characterized. For PMMA grating on a metallic film, the measured absorption bandwidth is 12 nm with a nearly 80% absorption at normal incidence. For gold grating on a metallic film, the measured absorption bandwidth is 40 nm with a nearly 70% absorption. Such spatially and spectrally resolved 2D nanostructure arrays with large angle sensitivities have potential applications in angle measurement, thermal emitters, optical filters, and biosensors.
Advanced Optical Materials, Vol.4, Issue 3, pp.488 (2016)


Controlling wave-vector of propagating surface plasmon polaritons on single-crystalline gold nanoplates
Chemically synthesized single-crystalline metal nanoplates with atomically flat surfaces provide favorable features compared with traditional polycrystalline metal films. The excitation and propagation of leaky SPPs on micrometer sized (10-20 μm) and thin (30 nm) gold nanoplates are investigated utilizing leakage radiation microscopy. By varying polarization and excitation positions of incident light on apexes of nanoplates, wave-vector (including propagation constant and propagation direction) distributions of leaky SPPs in Fourier planes can be controlled, indicating tunable SPP propagation.
Scientific Reports, Vol. 5, Article number: 13424 (2015)
Controlling the angular radiation of single emitters using dielectric patch nanoantennas
In this paper, we investigate the coupling between a single emitter and dielectric patch nanoantennas. For the coupled system involving non-spherical structures, analytical Mie theory is no longer applicable. A semi-analytical model is proposed instead to interpret the coupling mechanism and the radiation characteristics of the system. Following the guideline provided by the semi-analytical model,we demonstrate that the emission of a single emitter can be rotated by 90°utilizing the magnetic nature of the dielectric patch nanoantennas, which has not been shown before.
Appl. Phys. Lett. Vol. 107, pp. 031109 (2015)

Gold nanoparticle transfer through photothermal effects in a metamaterial absorber by nanosecond laser

A non-complicated, controllable method of metallic nanoparticle fabrication at low operating light power is proposed. The method is based on laser-induced forward transfer, using a metamaterial absorber as the donor to significantly enhance the photothermal effect and reduce the operating light fluence to 35 mJ/cm2, which is much lower than that in previous works. A large number of metallic nanoparticles can be transferred by one shot of focused nanosecond laser pulses. Transferred nanoparticles exhibit good size uniformity and the sizes are controllable. The optical properties of transferred particles are characterized by dark-field spectroscopy and the experimental results agree with the simulation results.
Scientific Reports, Vol. 4, Article number: 6080

Ultra-narrow-band light dissipation by a stack of lamellar silver and alumina

An ultra-narrow band absorber consisting of continuous silver and alumina  films is investigated. Owing to Fabry–Pérot resonance and  silver's  inherent loss, an ultra-narrowspectral range of light can be entirely trapped in the  structure. By varying thicknesses of metallic and dielectric films, absorption peak shifts in visible and near-infrared regions. When two suchmetal-insu-lator-metal stacks are cascaded, experimental results show that an ultra-narrow absorption bandwidth of 7 nm is achieved, though theoretical results give that of 2 nm. Features of high-efficiency and ultra-narrow band absorption have huge potential in optical filtering, thermal emitter design, etc.
Appl. Phys. Lett. Vol. 104, pp. 221107 (2014)


Grating-assisted enhanced optical transmission through a seamless gold film

In this paper, we experimentally demonstrate enhanced optical transmission through a seamless gold film based on the grating-insulator-metal (GIM) architecture. The transmittance of this GIM structure reaches 40% at 930 nm, showing 3.7 dB and 9.1 dB increase compared with a bare gold film and a continuous metal-insulator-metal stack, respectively. The enhanced transmission is polarization-sensitive and robust for oblique incidence. With tunable transmission peaks, such a device exhibits great potential for applications in optical filtering, polarization detecting and further integration in optoelectronics system.
Opt. Express, Vol. 22, Issue 5, pp.5416-5421 (2014)


Optimized grating as an ultra-narrow band absorber or plasmonic sensor

In this letter, lamellar gratings are investigated via temporal coupled-mode theory and numerical simulations. Total absorption can be achieved by an optimized grating with shallow grooves under normal incidence and the full width at half maximum (FWHM) is only 0.4 nm. For certain wavelengths, the structure shows high absorption only within an ultra-narrow angle, which suggests that it can be used as a highly directional thermal emitter according to Kirchhoff’s law. Besides, the resonant wavelength is sensitive to the refractive index of the environmental dielectric. The large sensitivity (1400 nm∕RIU) and simultaneous small FWHM result in a huge figure-of-merit of 2300∕RIU, which enables the structure to have great potential in plasmonic sensing.
Optics Letters, Vol. 39, Issue 5, pp. 1137-1140 (2014)


Plasmonic Sectoral Horn Nanoantennas

In this Letter, plasmonic sectoral horn nanoantennas working at near-infrared wavelength (1550 nm) have been investigated. We demonstrate that, although there are certain differences between the plasmonic and classical radiofrequency (RF) sectoral horn antennas, the plasmonic horns still possess a number of attractive features, like their RF counterparts, such as tunable high directivities, simplicity in fabrication, and ease of coupling to waveguides. As a specific application, we further show how to exploit these findings to optimize an optical wireless nanolink using the proposed horn nanoantennas, and obtain a 60-fold increase in the received power compared with the situation of matched dipole nanoantennas.
Optics Letters, Vol. 39, Issue 11, pp. 3204-3207 (2014)


Plasmonic wave propagation in silver nanowires: guiding modes or not?

Propagation modes and single-guiding-mode conditions of one-dimensional silver nanowires based surface plasmon polariton (SPP) waveguides versus the operating wavelength (500-2000 nm) are investigated. For silver nanowires immersed in a SiO2 matrix, both short-range SPP (SRSPP)-like modes and long-range SPP (LRSPP)-like modes can be guided. However, only the LRSPP-like modes have cutoff radii. For silver nanowires on a SiO2 substrate, the LRSPP-like modes cannot be supported due to asymmetry. While for the SRSPP-like guiding mode, it has a cutoff radius for wavelength longer than 615 nm. For wavelength shorter than 615 nm, there is no cutoff radius for the guiding modes due to the appearance of the interface modes and thus the single-guiding-mode operation is always satisfied.
Opt. Express, Vol.21, Issue 7, pp. 8587-8595 (2013)

Near-infrared broadband absorber with film-coupled multilayer nanorods

Turning the surfaces of noble metals (metasurfaces) into black (highly absorptive) surfaces can be potentially applied in thermophotovoltaics, sensing, tailoring thermal emissivity, etc. Here we demonstrate an extremely broadband absorber for the 900–1600 nm wavelength range with robust high absorption efficiency. The inexpensive droplet evaporation method is implemented to create patterns of nanoparticles dispersed on a gold film spaced by a thin dielectric layer. The diversity of the complicated random stacking of the chemically synthesized gold nanorods is the major factor for the broad absorption band. Such a metamaterial absorber may pave the way for cost-effective manufacture of large-area black metasurfaces.
Optics Letters, Vol. 38, Issue 13, pp. 2247-2249 (2013)