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Konig M.,Imperial College London | Konig M.,University of Duisburg - Essen | Rahmani M.,Imperial College London | Zhang L.,National University of Singapore | And 8 more authors.
ACS Nano | Year: 2015

Metal nanoclusters, sometimes called metamolecules or plasmonic oligomers, exhibit interesting optical properties such as Fano resonances and optical chirality. These properties promise a variety of practical applications, particularly in ultrasensitive biochemical sensing. Here we investigate experimentally the sensitivities of plasmonic pentamers and quadrumers to the adsorption of self-assembled nanometer-thick alkanethiol monolayers. The monolayer sensitivity of such oligomers is found to be significantly higher than that of single plasmonic nanoparticles and depends on the nanocluster arrangement, constituent nanoparticle shape, and the plasmon resonance wavelength. Together with full-wave numerical simulation results and the electromagnetic perturbation theory, we unveil a direct correlation between the sensitivity and the near-field intensity enhancement and spatial localization in the plasmonic hot spots generated in each nanocluster. Our observation is beyond conventional considerations (such as optimizing nanoparticle geometry or narrowing resonance line width) for improving the sensing performance of metal nanoclusters-based biosensors and opens the possibilities of using plasmonic nanoclusters for single-molecule detection and identification. © 2014 American Chemical Society. Source


Tang P.,Hunan University | Liu J.,Collaborative Innovation Center for Optoelectronic Science and Technology | Xu C.,Collaborative Innovation Center for Optoelectronic Science and Technology | Zhao C.,Hunan University | Wen S.,Hunan University
Applied Physics Express | Year: 2015

We experimentally show and report on a high-slope-efficiency, wavelength-locked, narrow-linewidth operation in a resonantly diode-pumped Erdoped yttrium aluminum garnet (Er:Y3Al5O12, Er:YAG) laser by using a volume Bragg grating (VBG) as a wavelength selector and an input mirror simultaneously. In this wavelength-locked operation, a maximum output power of 6.5W at 1645nm was achieved, which corresponds to a maximum slope efficiency of 105% with respect to the incident power. The small fluctuation of the lasing spectrum demonstrates good stability, with a 3 dB bandwidth of 0.06nm at the center wavelength. This result shows potential applications of the VBG for high-efficiency, wavelength-locked, narrow-linewidth, and highly stable Er:YAG lasers. © 2015 The Japan Society of Applied Physics. Source


Wang Z.,National University of Singapore | Wang Z.,Imperial College London | Dong Z.,Institute of Materials Research and Engineering of Singapore | Gu Y.,National University of Singapore | And 13 more authors.
Nature Communications | Year: 2016

Impressive properties arise from the atomically thin nature of transition metal dichalcogenide two-dimensional materials. However, being atomically thin limits their optical absorption or emission. Hence, enhancing their photoluminescence by plasmonic nanostructures is critical for integrating these materials in optoelectronic and photonic devices. Typical photoluminescence enhancement from transition metal dichalcogenides is 100-fold, with recent enhancement of 1,000-fold achieved by simultaneously enhancing absorption, emission and directionality of the system. By suspending WSe2 flakes onto sub-20-nm-wide trenches in gold substrate, we report a giant photoluminescence enhancement of ∼20,000-fold. It is attributed to an enhanced absorption of the pump laser due to the lateral gap plasmons confined in the trenches and the enhanced Purcell factor by the plasmonic nanostructure. This work demonstrates the feasibility of giant photoluminescence enhancement in WSe2 with judiciously designed plasmonic nanostructures and paves a way towards the implementation of plasmon-enhanced transition metal dichalcogenide photodetectors, sensors and emitters. Source


Jiang L.,Collaborative Innovation Center for Optoelectronic Science and Technology | Dai X.,Collaborative Innovation Center for Optoelectronic Science and Technology | Xiang Y.,Collaborative Innovation Center for Optoelectronic Science and Technology | Wen S.,Collaborative Innovation Center for Optoelectronic Science and Technology
IEEE Photonics Journal | Year: 2014

We have theoretically investigated the group delay of the TE-polarized beam reflected from a Fabry-Perot cavity with the insertion of the graphene sheets in the near-infrared band. It is shown that even a single-layer graphene allows for notable variation of group delay. Group delay can be enlarged negatively and can be switched from positive to negative, or vice versa. Importantly, the group delay depends on the Fermi energy of the graphene sheets, and thus, it can be actively controlled through electrical or chemical modification of the charge carrier density of the graphene. Furthermore, the influences of the position of graphene in the Fabry-Perot cavity, the mirror transmittance, and the number of graphene layers on group delay are clarified. © 2009-2012 IEEE. Source

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