Resonance characteristics of localized plasmonic structures with periodic ZnO nano-patterns

Localized plasmonic structures with the periodic ZnO nano-patterns are demonstrated to increase the sensing characteristics of plasmonic sensor. The ZnO nano-patterns with 30 and 50 nm thicknesses are formed on the Au thin film of 50 nm, which have the periodic nano-patterns of 300 nm. Localized plasmonic structures are optimized using the three-dimensional finite-difference time-domain method as a function of incident angle for the width and thickness of the ZnO nano-structures. Localized plasmonic structures with the periodic ZnO nano-holes are fabricated using the double exposure technique by laser interference lithography. The measured resonance angles of 47.5° and 54° are obtained in the localized plasmonic structures with the periodic ZnO nano-patterns of 30 and 50 nm thicknesses, respectively.     

Improving the efficiency of thin film tandem solar cells by plasmonic intermediate reflectors

Thin film tandem solar cells made of amorphous and microcrystalline silicon provide renewable energy at the benefit of low material consumption. As a drawback, these materials do not posses the high carrier mobilities of their crystalline counterpart which limits the feasible material thickness. For maintaining the light absorption as high as possible, photon management is required. Here we show that metallic nanodiscs that sustain localized plasmon polaritons can increase the efficiency of such solar cells if they are incorporated into the dielectric intermediate reflector separating the top and the bottom cell. We provide quantitative estimates for the possible absorption enhancement of optimized bi-periodic nanodiscs that are feasible for fabrication. Emphasis is also put on discussing the impact of obliquely incident sun light on the solar cell performance.     

Partially coherent bidirectional reflectance distribution data computation for modeling periodic plasmonic structures at infrared wavelengths

A series of methods for employing Rigorous Coupled Wave Analysis (RCWA) to predict bidirectional reflectance distributions for periodic plasmonic surface structures, under partial longitudinal spatial coherence conditions, is presented. Two new methods are presented, which accurately represent the effects of directionally dependent absorption on the profiles of reflected diffraction lobes. Bidirectional reflectance distribution functions may be fit to the resulting bidirectional reflectance distributions, allowing plasmonic structures to be accurately incorporated into infrared scene-rendering and component modeling tools.     

On the use of a hierarchical multi-level building block basis function scheme in periodic plasmonic structures

A Volumetric Method of Moments algorithm is applied to predict the plasmonic responses of chiral metamaterials. This algorithm is based on the use of a multi-level building block basis function scheme, in combination with a dedicated Kummer transformation in the calculation of periodic Green’s functions. The validity of the algorithm is demonstrated by analyzing a Ninja Star periodic structure. A good agreement can be found between simulation and experiment.     

Design of plasmonic nanoantennae for enhancing spontaneous emission

We apply two- and three-dimensional numerical calculations to study optical nanoantennae made of two coupled gold nanostructures, enclosing a single emitter in their gap. We show that, using structures manufacturable with today's nanotechnology, it is possible to increase the radiative decay rate by three orders of magnitude while keeping a quantum efficiency larger than 80% in the near-infrared regime. We examine the competition between the radiative and nonradiative processes in the presence of the antennae as a function of wavelength and antenna geometry. Our results hold great promise for improving the quantum efficiency of poor emitters such as silicon nanocrystals or carbon nanotubes.     

Hybrid plasmonic waveguides for low-threshold nanolaser applications

We propose new types of hybrid plasmonic waveguides for low-threshold nanolaser applications. Modal properties and lasing threshold under different geometric shapes and parameters are investigated and analyzed by the finite element method, aiming to realize both low propagation and high field confinement. Results show that a smaller gap width and a larger round corner radius of the metal film reduce the lasing threshold. These new structures can open up new avenues in the fields of active plasmonic circuits.     

Reduced scattering-matrix algorithm for high-density plasmonic structures

We describe a method to compute S-matrix interface terms using a selection of eigenmodes. When solving the modal equation, the computation of left and right eigenvectors leads to rectangular eigenmodes matrices. Expressions of S-matrix interface terms are then expressed so as to allow for a significant reduction of the computation cost. The reduction is even further decreased in the case of the B-spline modal method, which deals with sparse matrices. Its convergence is illustrated on a high-density plasmonic structure and compared to a full modal method.     

Gain-assisted indented plasmonic waveguide for low-threshold nanolaser applications

A subwavelength plasmonic indented waveguide with an active InGaAsP core is proposed.The characteristics of the gap plasmon mode and gain required for lossless propagation are investigated and analyzed by the finite element method.We numerically calculate the normalized mode areas and percentages of energy confined in InGaAsP and metal for plasmonic nanolaser applications.It is shown that the indentation of the sidewalls has an optimal value for which the lasing threshold gain is minimal.The structure could enable low-threshold subwavelength lasing and applications for optoelectronic integrated circuits.     

Hot spots enriched plasmonic nanostructure-induced random lasing of quantum dots thin film

Here,a plasmon-enhanced random laser was achieved by incorporating gold nanostars(NS) into disordered polymer and Cd Se/Zn S quantum dots(QDs) gain medium films,in which the surface plasmon resonance of gold NS can greatly enhance the scattering cross section and bring a large gain volume.The random distribution of gold NS in the gain medium film formed a laser-mode resonator.Under a single-pulse pumping,the scattering center of gold NS-based random laser exhibits enhanced performance of a lasing threshold of 0.8 m J/cm~2 and a full width as narrow as 6 nm at half maximum.By utilizing the local enhancement characteristic of the electric field at the sharp apexes of the gold NS,the emission intensity of the random laser was increased.In addition,the gold NS showed higher thermal stability than the silver nanoparticles,withstanding high temperature heating up to 200?C.The results of metal nanostructures with enriched hot spots and excellent temperature stability have tremendous potential applications in the fields of biological identification,medical diagnostics,lighting,and display devices.     

Femtosecond laser-induced periodic surface structures on steel and titanium alloy for tribological applications

Laser-induced periodic surface structures (LIPSS, ripples) were generated on stainless steel (100Cr6) and titanium alloy (Ti6Al4V) surfaces upon irradiation with multiple femtosecond laser pulses (pulse duration 30 fs, central wavelength 790 nm). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning geometry for the processing of large surface areas (5 × 5 mm²) covered homogeneously by the nanostructures. The irradiated surface regions were subjected to white light interference microscopy and scanning electron microscopy revealing spatial periods around 600 nm. The tribological performance of the nanostructured surface was characterized by reciprocal sliding against a ball of hardened steel in paraffin oil and in commercial engine oil as lubricants, followed by subsequent inspection of the wear tracks. For specific conditions, on the titanium alloy a significant reduction of the friction coefficient by a factor of more than two was observed on the laser-irradiated (LIPSS-covered) surface when compared to the non-irradiated one, indicating the potential benefit of laser surface structuring for tribological applications.     

Research progress of low-dimensional metal halide perovskites for lasing applications

Metal halide perovskites have been regarded as remarkable materials for next-generation light-harvesting and light emission devices. Due to their unique optical properties, such as high absorption coefficient, high optical gain, low trappingstate density, and ease of band gap engineering, perovskites promise to be used in lasing devices. In this article, the recent progresses of microlasers based on reduced-dimensional structures including nanoplatelets, nanowires, and quantum dots are reviewed from both fundamental photophysics and device applications. Furthermore, perovskite-based plasmonic nanolasers and polariton lasers are summarized. Perspectives on perovskite-based small lasers are also discussed. This review can serve as an overview and evaluation of state-of-the-art micro/nanolaser science.     

Ultra-compact two-dimensional plasmonic nano-ring antenna array for sensing applications

In this paper, a novel optical nanoantenna based on two-dimensional plasmonic nano-ring antenna array is proposed, investigated numerically and compared with a nano-disk antenna array. The results show that the nano-ring structure has resonances similar to the resonances of nano-disk structure but in higher wavelengths. These resonances are tunable by varying the structural parameters of the ring. The optical properties of the proposed structure are investigated in the context of designing a plasmonic refractive index sensor. The nano-ring antenna array sensor has large sensitivity in comparison to the conventional nano-disk antenna arrays. The special feature of the presented structure and the device concepts introduced in this work are applicable in realization of various integrated components and could play an important role in development of plasmonic sensors.     

Collective spontaneous emission of dye molecules and lasing

The threshold pump power density for lasing in dye solutions is found to depend on the photon energy of pumping radiation. An increase in the pumping photon energy can significantly lower the threshold pump power of dye lasers. For an ethanol solution of rhodamine 6G with a concentration of 4×10¹⁸ cm^?3, the threshold power density for pumping radiation with a wavelength of 532 nm is 20-fold higher than for pumping radiation with a wavelength of 347 nm. This phenomenon is associated with the competition of collective spontaneous emission, which can lead to the efficient deactivation of excited molecules in femtosecond times, and the dephasing of excited molecules due to the intramolecular nonradiative processes of absorbed-energy conversion. An increase in the dephasing rate with the increasing energy of exciting photons lowers the efficiency of collective spontaneous emission and increases the concentration of dephased excited molecules responsible for lasing.     

Nearly perfect metamaterial plasmonic absorbers for solar energy applications

In this study, two different approaches for the design of broadband polarization-independent wide-angle metamaterial plasmonic absorbers (MPA) are presented. The proposed MPAs are made of periodic arrays of Nickel (Ni) or Wolfram (W) cubes. The top surfaces of the cubes are texturized using silicon dioxide (SiO₂). The proposed PMAs with two different optimized textures experience plasmonic resonance characteristics that enable near unity visible light absorption. The parametric studies carried on the proposed MPAs with the aid of 3D-FDTD method results in wide-angle near perfect absorption characteristic that is >?0.96 for all visible regimes. Additionally, the obtained results show almost perfect absorption of above 99% over the frequency ranges extending from?~?458 to?~?525 and?~?489 to?~?665 THz. Besides, numerical results demonstrate that the proposed PMAs also exhibit both polarization and angle independency for the whole visible regime. Further, the absorption characteristics of proposed MPAs near the infrared and ultraviolet regimes are investigated.     

Fluorescent and lasing whispering gallery mode microresonators for sensing applications

Whispering gallery modes (WGMs) have been exploited for a broad range of sensing applications. However, the vast majority of WGM sensors consist of passive resonators, requiring complex interrogation systems to be employed, ultimately limiting their practicality. Active resonators containing a gain medium, allowing remote excitation and collection of the WGM‐modulated fluorescence spectra, have emerged as an alternative to passive resonators. Although research is still in its infancy, recent progress has reduced the performance gap between the two paradigms, fueled by the potential for new applications that could not previously be realized. Here, recent developments in sensors based on active WGM microresonators are reviewed, beginning with a discussion of the theory of fluorescence‐based and lasing WGMs, followed by a discussion of the variety of gain media, resonator architectures, and emerging sensing applications. We conclude with a discussion of the prospects and future directions for improving active WGM sensors.

     

Observation of the spin-based plasmonic effect in nanoscale structures

Observation of surface-plasmon phenomena that are dependent upon the handedness of the circularly polarized incident light (spin) is presented. The polarization-dependent near-field intensity distribution obtained in our experiment is attributed to the presence of a geometric phase arising from the interaction of light with an anisotropic and inhomogeneous nanoscale structure. A near-field vortex surface mode with a spin-dependent topological charge was obtained in a plasmonic microcavity. The remarkable phenomenon of polarization-sensitive focusing in a plasmonic structure was also demonstrated.