scholarly journals Optical near-field mapping of plasmonic nanostructures prepared by nanosphere lithography

2018 ◽  
Vol 9 ◽  
pp. 1536-1543 ◽  
Author(s):  
Gitanjali Kolhatkar ◽  
Alexandre Merlen ◽  
Jiawei Zhang ◽  
Chahinez Dab ◽  
Gregory Q Wallace ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Hot Spots ◽  
Near Field ◽  
Nanosphere Lithography ◽  
Plasmonic Nanostructures ◽  
Far Field ◽  
Optical Images ◽  
Spatial Frequencies ◽  
Comparison Of The Results ◽  
Non Destructive

We introduce a simple, fast, efficient and non-destructive method to study the optical near-field properties of plasmonic nanotriangles prepared by nanosphere lithography. Using a rectangular Fourier filter on the blurred signal together with filtering of the lower spatial frequencies to remove the far-field contribution, the pure near-field contributions of the optical images were extracted. We performed measurements using two excitation wavelengths (532.1 nm and 632.8 nm) and two different polarizations. After the processing of the optical images, the distribution of hot spots can be correlated with the topography of the structures, as indicated by the presence of brighter spots at the apexes of the nanostructures. This technique is validated by comparison of the results to numerical simulations, where agreement is obtained, thereby confirming the near-field nature of the images. Our approach does not require any advanced equipment and we suggest that it could be applied to any type of sample, while keeping the measurement times reasonably short.

scholarly journals Coupling Methodology for Studying the Far Field Effects of Wave Energy Converter Arrays over a Varying Bathymetry

Energies ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2899 ◽  
Author(s):  
Gael Verao Fernandez ◽  
Philip Balitsky ◽  
Vasiliki Stratigaki ◽  
Peter Troch
Keyword(s):  
Numerical Simulations ◽  
Wave Energy ◽  
Near Field ◽  
Coupled Model ◽  
Propagation Model ◽  
Irregular Waves ◽  
Computational Time ◽  
Far Field ◽  
Field Effects ◽  
Numerical Tool

For renewable wave energy to operate at grid scale, large arrays of Wave Energy Converters (WECs) need to be deployed in the ocean. Due to the hydrodynamic interactions between the individual WECs of an array, the overall power absorption and surrounding wave field will be affected, both close to the WECs (near field effects) and at large distances from their location (far field effects). Therefore, it is essential to model both the near field and far field effects of WEC arrays. It is difficult, however, to model both effects using a single numerical model that offers the desired accuracy at a reasonable computational time. The objective of this paper is to present a generic coupling methodology that will allow to model both effects accurately. The presented coupling methodology is exemplified using the mild slope wave propagation model MILDwave and the Boundary Elements Methods (BEM) solver NEMOH. NEMOH is used to model the near field effects while MILDwave is used to model the WEC array far field effects. The information between the two models is transferred using a one-way coupling. The results of the NEMOH-MILDwave coupled model are compared to the results from using only NEMOH for various test cases in uniform water depth. Additionally, the NEMOH-MILDwave coupled model is validated against available experimental wave data for a 9-WEC array. The coupling methodology proves to be a reliable numerical tool as the results demonstrate a difference between the numerical simulations results smaller than 5% and between the numerical simulations results and the experimental data ranging from 3% to 11%. The simulations are subsequently extended for a varying bathymetry, which will affect the far field effects. As a result, our coupled model proves to be a suitable numerical tool for simulating far field effects of WEC arrays for regular and irregular waves over a varying bathymetry.

Far-Field Performances Prediction of High Frequency Projectors Using Secondary Source Array Method

2016 ◽  
Vol 25 (02) ◽  
pp. 1750002 ◽  
Author(s):  
Shiquan Wang
Keyword(s):  
High Frequency ◽  
Near Field ◽  
Directivity Pattern ◽  
Field Method ◽  
Voltage Response ◽  
Secondary Source ◽  
Far Field ◽  
Comparison Of The Results ◽  
Source Array ◽  
Good Agreement

This paper investigates the prediction of the far-field performances of high frequency projectors using the second source array method (SSAM). The far-field parameters can be calculated accurately using the complex acoustic pressure data of two very close parallel planes which lie in the near-field region of the projector. The paper simulates the feasibility of predicting the far-field parameters such as transmitting voltage response and the far-field directivity pattern. The predicting results are compared with that calculated using boundary element method (BEM). It shows very good agreement between the two methods. A planar high frequency projector is measured using the near-field method. In order to verify the predicting results, the far-field measurement is performed for the same projector. The comparison of the results shows that the near-field method is capable to precisely predict the far-field parameters of the projector.

scholarly journals On the Large Near-Field Enhancement on Nanocolumnar Gold Substrates

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Pablo Díaz-Núñez ◽  
José Miguel García-Martín ◽  
María Ujué González ◽  
Raquel González-Arrabal ◽  
Antonio Rivera ◽  
...  
Keyword(s):  
Hot Spots ◽  
Near Field ◽  
Broad Band ◽  
Field Enhancement ◽  
Surface Enhanced Raman Spectroscopy ◽  
Plasmonic Nanostructures ◽  
Surface Enhanced ◽  
Surface Enhanced Raman ◽  
Nanostructured Gold ◽  
High Roughness

Abstract One of the most important and distinctive features of plasmonic nanostructures is their ability to confine large electromagnetic fields on nanometric volumes; i.e., the so-called hot spots. The generation, control and characterization of the hot spots are fundamental for several applications, like surface-enhanced spectroscopies. In this work, we characterize the near-field distribution and enhancement of nanostructured gold thin films fabricated by glancing angle deposition magnetron sputtering. These films are composed of columnar nanostructures with high roughness and high density of inter-columnar gaps, where the electromagnetic radiation can be confined, generating hot spots. As expected, the hot spots are localized in the gaps between adjacent nanocolumns and we use scattering-type scanning near-field optical microscopy to image their distribution over the surface of the samples. The experimental results are compared with finite-difference time-domain simulations, finding an excellent agreement between them. The spectral dependence of the field-enhancement is also studied with the simulations, together with surface-enhanced Raman spectroscopy at different excitation wavelengths in the visible-NIR range, proving a broad-band response of the substrates. These findings may result in interesting applications in the field of surface-enhanced optical spectroscopies or sensing.

Box-Scan: A Novel 3DXRD Method for Studies of Recrystallization and Grain Growth

2012 ◽  
Vol 715-716 ◽  
pp. 518-520 ◽  
Author(s):  
Allan Lyckegaard ◽  
Henning Friis Poulsen ◽  
Wolfgang Ludwig ◽  
Richard W. Fonda ◽  
Erik M. Lauridsen
Keyword(s):  
Spatial Resolution ◽  
Near Field ◽  
Polycrystalline Materials ◽  
High Temporal Resolution ◽  
Far Field ◽  
X Ray Diffraction ◽  
The Individual ◽  
Individual Grains ◽  
Non Destructive

Within the last decade a number of x-ray diffraction methods have been presented for non-destructive 3D characterization of polycrystalline materials. 3DXRD [1] and Diffraction Contrast Tomography [2,3,4] are examples of such methods providing full spatial and crystallographic information of the individual grains. Both methods rely on specially designed high-resolution near-field detectors for acquire the shape of the illuminated grains, and therefore the spatial resolution is for both methods limited by the resolution of the detector, currently ~2 micrometers. Applying these methods using conventional far-field detectors provides information on centre of mass, crystallographic orientation and stress state of the individual grains [5], at the expense of high spatial resolution. However, far-field detectors have much higher efficiency than near-field detectors, and as such are suitable for dynamic studies requiring high temporal resolution and set-ups involving bulky sample environments (e.g. furnaces, stress-rigs etc.)

scholarly journals Light-induced symmetry breaking for enhancing second-harmonic generation from an ultrathin plasmonic nanocavity

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Guang-Can Li ◽  
Dangyuan Lei ◽  
Meng Qiu ◽  
Wei Jin ◽  
Sheng Lan ◽  
...  
Keyword(s):  
Second Harmonic Generation ◽  
Harmonic Generation ◽  
Noble Metals ◽  
Second Harmonic ◽  
Near Field ◽  
Field Enhancement ◽  
Plasmonic Nanostructures ◽  
Far Field ◽  
Field Amplification ◽  
Gold Nanosphere

AbstractEfficient frequency up-conversion of coherent light at the nanoscale is highly demanded for a variety of modern photonic applications, but it remains challenging in nanophotonics. Surface second-order nonlinearity of noble metals can be significantly boosted up by plasmon-induced field enhancement, however the related far-field second-harmonic generation (SHG) may also be quenched in highly symmetric plasmonic nanostructures despite huge near-field amplification. Here, we demonstrate that the SHG from a single gold nanosphere is significantly enhanced when tightly coupled to a metal film, even in the absence of a plasmon resonance at the SH frequency. The light-induced electromagnetic asymmetry in the nanogap junction efficiently suppresses the cancelling of locally generated SHG fields and the SH emission is further amplified through preferential coupling to the bright, bonding dipolar resonance mode of the nanocavity. The far-field SHG conversion efficiency of up to $$3.56\times 10^{-7}$$ 3.56 × 1 0 − 7 W−1 is demonstrated from a single gold nanosphere of 100 nm diameter, two orders of magnitude higher than for complex double-resonant plasmonic nanostructures. Such highly efficient SHG from a metal nanocavity also constitutes an ultrasensitive nonlinear nanoprobe to map the distribution of longitudinal vectorial light fields in nanophotonic systems.

Studies on Novel Hyperlens Concept for Ultrasonic Non Destructive Evaluation

2021 ◽  
Author(s):  
Pradeep Kumar ◽  
Mohamed Subair Syed Akbar Ali ◽  
Prabhu Rajagopal
Keyword(s):  
Near Field ◽  
Ultrasonic Imaging ◽  
Super Resolution ◽  
Cost Effective ◽  
Medical Diagnostics ◽  
Evanescent Waves ◽  
Far Field ◽  
Resolution Limit ◽  
Non Destructive Evaluation ◽  
Non Destructive

Abstract Ultrasonic imaging is widely preferred in the field of non-destructive evaluation, medical diagnostics, and underwater inspection because it offers various advantages such as safety and versatility. However, conventional ultrasonic imaging methods suffer from the poor resolution limit imposed by the loss of information on fine features within the near-field. Metamaterial concepts have attracted much research interest in recent years, yielding extraordinary benefits such as super-resolution imaging, vibration damping, and cloaking. In the context of imaging, Metalenses allow the successful transfer of the information carried by the evanescent waves to far-field by amplifying them and hence help in overcoming the resolution limit. Hyperlenses enable subwavelength resolution along with spatial magnification by transforming evanescent waves scattered past a material artifact into propagating waves at the far-field ‘imaging’ end of the medium. This paper discusses novel radially symmetric ultrasonic hyperlens for imaging defects in the context of non-destructive evaluation, a topic that has not been studied much. The effect of parameters such as defect extent and distance between the lens on the subwavelength imaging of the hyperlens is studied using numerical simulations. This study investigates the magnification achievable using the proposed hyperlens and the effectiveness of this approach for nondestructive evaluation using cost-effective ‘everyday’ transducers.

scholarly journals Asymptotic solutions for turbulent mass transfer at high Schmidt number

2012 ◽  
Vol 468 (2142) ◽  
pp. 1676-1695 ◽  
Author(s):  
Maarten van Reeuwijk ◽  
Kaveh Sookhak Lari
Keyword(s):  
Mass Transfer ◽  
Numerical Simulations ◽  
Schmidt Number ◽  
Near Field ◽  
Far Field ◽  
Good Correspondence ◽  
Closed Form Solutions ◽  
High Schmidt Number ◽  
Fully Developed Turbulent Flow ◽  
Good Agreement

We present closed-form solutions for high Schmidt number mass transfer in a hydrodynamically fully developed turbulent flow. Governing equations for the near- and far-field are developed for a large class of boundary conditions (BCs) for which the mass flux is a function of the concentration at the wall. We show that for this class of BCs, which includes nonlinear wall reactions, the mass transfer coefficient is independent of the BC and the Sherwood correlation is therefore universal. For Dirichlet, Neumann and Robin BCs, the far-field solutions are in good correspondence with the method of separating variables and near-field solutions are in good agreement with numerical simulations. However, in contrast with the far-field solutions, the Sherwood correlation in the near-field depends on the specific BC. As an example of nonlinear BCs, solutions for a second-order wall reaction are derived which are compared with numerical simulations and found to be in excellent agreement.

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