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What is Time at the Basic Level?

Abstract

Plasmonic nanocavities comprised of metal film-coupled nanoparticles have emerged as a versatile nanophotonic platform benefiting from their ultrasmall mode volume and large Purcell factors. In the weak-coupling regime, the particle-film gap thickness affects the photoluminescence (PL) of quantum emitters sandwiched therein. Here, we investigated the Purcell effect-enhanced PL of monolayer MoS2 inserted in the gap of a gold nanoparticle (AuNP)–alumina (Al2O3)–gold film (Au Film) structure. Under confocal illumination by a 532 nm CW laser, we observed a 7-fold PL peak intensity enhancement for the cavity-sandwiched MoS2 at an optimal Al2O3 thickness of 5 nm, corresponding to a local PL enhancement of ∼350 by normalizing the actual illumination area to the cavity’s effective near-field enhancement area. Full-wave simulations reveal a counterintuitive fact that radiation enhancement comes from the non-central area of the cavity rather than the cavity center. By scanning an electric dipole across the nanocavity, we obtained an average radiation enhancement factor of about 65 for an Al2O3 spacer thickness of 4 nm, agreeing well with the experimental thickness and indicating further PL enhancement optimization. Our results indicate the importance of configuration optimization, emitter location and excitation condition when using such plasmonic nanocavities to modulate the radiation properties of quantum emitters.

Abstract

Integration of quantum emitters in photonic structures is an important step in the broader quest to generate and manipulate on-demand single photons via compact solid-state devices. Unfortunately, implementations relying on material platforms that also serve as the emitter host often suffer from a tradeoff between the desired emitter properties and the photonic system practicality and performance. Here, we demonstrate “pick and place” integration of a Si3N4 microdisk optical resonator with a bright emitter host in the form of ∼20-nm-thick hexagonal boron nitride (hBN). The film folds around the microdisk maximizing contact to ultimately form a hybrid hBN/Si3N4 structure. The local strain that develops in the hBN film at the resonator circumference deterministically activates a low density of defect emitters within the whispering gallery mode volume of the microdisk. These conditions allow us to demonstrate cavity-mediated out-coupling of emission from defect states in hBN through the microdisk cavity modes. Our results pave the route toward the development of chip-scale quantum photonic circuits with independent emitter/resonator optimization for active and passive functionalities.

Abstract

Lanthanide up-conversion features stepwise multi-photon processes, where the difference in photon number that is required for specific up-conversion process usually leads to significant variance in pumping-related processes/properties. In this work, a pumping-controlled dual-mode anti-counterfeiting strategy is conceived by taking advantage of the combination of up-conversion processes with different photon numbers. The combination of Er3+ and Tm3+, which are spatially separated within a designed core/triple-shell nano-architecture, is taken as an example to illustrate such idea. Upon infrared excitation, the emission color of a designed pattern can be switched from red to purple by increasing the excitation power density from 5 to 11 W/cm2, while a bright luminescent trajectory including red, white and blue-green color with different length is observed when rotating the pattern above 600 rpm. In addition, the relative up-conversion emission intensities of the Er3+ and Tm3+ ions can be manipulated through tailoring interfacial or inner defects in the core/triple-shell nano-crystals, which enable an ultrahigh sensitivity for the pumping-controlled emission color variation to be observed under excitation power well below 11 W/cm2.

Abstract

Analysing dynamics of a single biomolecule using high-resolution imaging techniques has been had significant attentions to understand complex biological system. Among the many approaches, vertical nanopillar arrays in contact with the inside of cells have been reported as a one of useful imaging applications since an observation volume can be confined down to few-tens nanometre theoretically. However, the nanopillars experimentally are not able to obtain super-resolution imaging because their evanescent waves generate a high optical loss and a low signal-to-noise ratio. Also, conventional nanopillars have a limitation to yield 3D information because they do not concern field localization in z-axis. Here, we developed novel hybrid nanopillar arrays (HNPs) that consist of SiO2 nanopillars terminated with gold nanodisks, allowing extreme light localization. The electromagnetic field profiles of HNPs are obtained through simulations and imaging resolution of cell membrane and biomolecules in living cells are tested using one-photon and 3D multiphoton fluorescence microscopy, respectively. Consequently, HNPs present approximately 25 times enhanced intensity compared to controls and obtained an axial and lateral resolution of 110 and 210 nm of the intensities of fluorophores conjugated with biomolecules transported in living cells. These structures can be a great platform to analyse complex intracellular environment.

Abstract

Cherenkov radiation (CR) is the electromagnetic shockwaves generated by the uniform motion of charged particles at a velocity exceeding the phase velocity of light in a given medium. In the Reststrahlen bands of hexagonal boron nitride (hBN), hyperbolic phonon polaritons (HPPs) are generated owing to the coupling between mid-infrared electromagnetic waves and strong anisotropic lattice vibrations. This study theoretically and numerically investigates the generation of volume CR based on HPPs in hBN with super-large wavevectors. Results reveal that CR can be generated using free electrons with an extremely low kinetic energy of 1 eV—two orders of magnitude lower than that reported in extant studies. The findings of this investigation provide new insights into significantly reducing the electron energy required for CR generation and potentially open new research avenues in the fields of CR and HPP.

Abstract

Cherenkov radiation in natural transparent materials is generally forward-propagating, owing to the positive group index of radiation modes. While negative-index metamaterials enable reversed Cherenkov radiation, the forward photon emission from a swift charged particle is prohibited. In this work, we theoretically investigate emission behaviours of a swift charged particle in the nanometallic layered structure. Our results show that Cherenkov photons are significantly enhanced by longitudinal plasmon modes resulting from the spatial nonlocality in metamaterials. More importantly, longitudinal Cherenkov photons can be directed either forward or backward, stringently depending on the particle velocity. The enhanced flexibility to route Cherenkov photons holds promise for many practical applications of Cherenkov radiation, such as novel free-electron radiation sources and new types of Cherenkov detectors.

Abstract

We report a new strategy for the design of organic light emitting diodes (OLEDs), where nanoscale OLEDs are fabricated into a large-area periodic array with their emission propagating along the active layer and being coupled out through the end facets. A large-area template dielectric grating is produced by interference lithography. The OLED devices are then produced on the side walls of the template grating lines, where each device is carried by the back of a grating line and has a width of <300 nm and a height of about 270 nm. The emission is coupled out of the device on the end facet window after a maximum propagation length of shorter than 300 nm through the active layer, reducing largely metallic absorption by the electrodes and overcoming the optical loss by waveguide confinement. Furthermore, such a configuration enables directional concentration of the output emission. The nanoscale OLEDs also imply large potentials for integration into optoelectronic systems.

Abstract

Plasmonic nanolasers are a new class of laser devices which amplify surface plasmons instead of photons by stimulated emission. A plasmonic nanolaser cavity can lower the total cavity loss by suppressing radiation loss via the plasmonic field confinement effect. However, laser size miniaturization is inevitably accompanied with increasing total cavity loss. Here we reveal quantitatively the loss and gain in a plasmonic nanolaser. We first obtain gain coefficients at each pump power of a plasmonic nanolaser via analyses of spontaneous emission spectra and lasing emission wavelength shift. We then determine the gain material loss, metallic loss and radiation loss of the plasmonic nanolaser. Last, we provide relationships between quality factor, loss, gain, carrier density and lasing emission wavelength. Our results provide guidance to the cavity and gain material optimization of a plasmonic nanolaser, which can lead to laser devices with ever smaller cavity size, lower power consumption and faster modulation speed.

Abstract

MXene are a class of metal carbide and metal nitride materials with a two-dimensional layered structure. MXene Ti3C2Tx has the characteristics of good metal conductivity and adjustable chemical composition, which has attracted the attention of scientists. Recently, Mxene have shown strong nonlinear photonics and optoelectronic effect, which can be used to generate ultrashort pulsed laser. However, soliton molecules pulse in laser cavity based on Mxene have not been reported at present. In this article, MXene have been characterized systematically, and the nonlinear optical characters were measured. In addition, we combined MXene with taper fiber to make a saturable absorber device for an erbium-doped fiber laser. The modulation depth and saturation absorption intensity of MXene are 10.3% and 197.5 MW/cm2, respectively. Thanks to the outstanding character of MXene, a three-order soliton molecules pulse were generated in laser cavity. The center wavelength, pulse interval and spectral modulation period of soliton molecules are 1529.4 nm, 15.5 ps and 0.5 nm, respectively. The above experimental results show that MXene have broad application prospects in the fields of optical fiber communication, laser material processing and high-resolution optics.