Redistribution Of Electromagnetic Field Research Articles

Near‐Field Mediated 40 nm In‐Volume Glass Fabrication by Femtosecond Laser

AbstractNanofabrication techniques have significantly impelled the development of nanomechanics and nanophotonics by making nano‐precision material processing routine. Although widely employed, current sub‐100 nm nanofabrication approaches based on focused particles or light are limited to surface modification. Here, an optical in‐volume fabrication approach that enables 3D glass processing with a spatial resolution down to 40 nm is demonstrated. Such an approach is based on the formation of a single nanoslit structure induced by femtosecond laser pulses. Spatially‐variant nanopatterns with uniform line‐widths are then formed by a near‐field mediated intensity redistribution of incident light. The redistribution of electromagnetic field induced by the presence of the nanoslit leads to a positive‐feedback self‐assembly process. The self‐assembly process allows achieving spacing one order of magnitude smaller than the laser beam size. In addition, a tilted ablation front that results in the generation of structures with curved morphology is revealed. The proposed approach enables 3D patterning with a lateral spacing down to 200 nm and 5D optical data storage with an equivalent capacity of 7.2 TB per disk, demonstrating its feasibility for 3D nanoscale processing in bulk materials.

Strong confinement of gap modes induced by the film modified electric and magnetic modes in dielectric nanoparticle dimers

Nanogaps are one of the most useful systems in nanooptics. The gap modes in a film coupled dielectric nanoparticle dimer system are influenced by both of the film and the electric and magnetic modes of the particles. In this work, strong confinement of gap modes of dielectric (Si) nanoparticle dimer on Au/Si film is investigated. The results show an abnormal electric field enhancement obtained between Si nanoparticle dimer on metal film, which is attributed to film coupled electric and magnetic dipole modes in dielectric nanoparticle dimer. The results are further analyzed with mode hybridization theory. Furthermore, the surface enhanced Raman spectroscopy (SERS) is performed to demonstrate these theoretical analyses. The film induced electromagnetic field redistribution in dielectric nanoparticle dimer not only extend the knowledge of dielectric gap modes but also has tremendous applications, e.g. light manipulating in subwavelength, light harvest, surface enhanced spectrum, etc.

Nanoparticle assisted Raman information acquisition from metal encapsulated sandwich structure

For the induced image charge on surface, the metal film as a substrate brings the metal nanostructures some novel surface plasmon‐related phenomenon, e.g. electromagnetic field redistribution and energy focusing. In this work, the surface‐enhanced Raman scattering in sandwich structure consist of Au nanoplate and Au film adsorbed with molecule monolayer is investigated. The surface‐enhanced Raman scattering spectra point out that the shielded Raman signals of molecule under metal nanoplate could be collected from this metal‐encapsulated sandwich structure with the help of nanoparticle. This interesting phenomenon is further confirmed by the simulated electromagnetic field where the light power in the gap between Au nanoplate and Au film is greatly enhanced with a nanoparticle located. The further results also demonstrate this nanoparticle assisted Raman information acquisition is highly influenced by the thickness of encapsulated nanoplate and size of nanoparticle. Furthermore, the positive results of nanoparticles with different shapes in this interesting phenomenon provide an extensive application prospects including surface‐enhanced Raman scattering detection, light information storage and selective harvesting, location detection of light information, photocatalysis, etc. Copyright © 2016 John Wiley & Sons, Ltd.

Frequency Stop Band in an Air-Voided ZnO Photonic Crystal: A Dispersion Diagram Based Design

to catch a glimpse of the action inside of the small space, can aid better thin film designs. In the non-linear anisotropic regime the results of such interactions provide important insights into the bulk level behavior of matter. Using this approach, a zinc oxide (ZnO) based photonic crystal is designed with spherical air voids. A Gaussian continuous wave excitation of the refractive index contrast (ZnO=1.9 and Air =1) photon waveguide generated thus, is characterized for the redistribution of electromagnetic field. When, centered at a specific wavelength (1.9 m), the graph of the frequencies that can exist inside the crystal, is plotted against the limited k-space vector. The dispersion diagram that emerges shows a band of frequency states that cannot exist inside such a design. Physically this constitutes a k-space which is devoid of any detectable disturbances. Crystallographically, the reduced Brilluoin zone can be used to make a thin layer of ZnO that can act as a frequency stop layer, in a real multilayered photoelectric device.

Heterodimer Nanostructures Induced Energy Focusing on Metal Film

As an interesting surface plasmon phenomenon discovered several years ago, electromagnetic field redistribution in nanoparticle dimer on film system provides a novel thought to enhance the light power on a plain film which could been widely used in surface enhanced Raman scattering (SERS), solar cells, photo-catalysis, etc. Homodimers on film are mainly investigated in past years, while the properties of heterodimers on film are still unclear. In this work, size difference induced electromagnetic field redistribution in Ag nanoparticle dimer on Au film system is investigated first. The results obtained from finite element method indicate that the smaller nanoparticle has much greater ability to focus light energy on Au film, which even reached more than 5 time compared to the larger one. Further researches indicate that this energy focusing ability has a strong relationship to the wavelength and diameter ration in dimer. Similar focusing phenomenon is found in the system of thick wire-smaller particle on film. Later, the SERS spectra collected in the small nanoparticle-large nanowire system provide an experimental evidence for this theoretic predication. Our results strengthen the understanding of surface plasmon on plane film and have potential application prospects in the surface plasmon related fields.

Investigation of the polarization-dependent optical force in optical tweezers by using generalized Lorenz-Mie theory

In vectorial diffraction theory, tight focusing of a linearly polarized laser beam produces an anisotropic field distribution around the focal plane. We present a numerical investigation of the electromagnetic field distribution of a focused beam in terms of the input beam polarization state and the associated effects on the trap stiffness asymmetry of optical tweezers. We also explore the symmetry change of a polarization-dependent optical force due to the electromagnetic field redistribution by the presence of dielectric spheres of selected diameters ranging from the Rayleigh scattering regime to the Mie scattering regime.

Electromagnetic field redistribution induced selective plasmon driven surface catalysis in metal nanowire-film systems.

For the novel interpretation of Raman spectrum from molecule at metal surface, the plasmon driven surface catalysis (PDSC) reactions have become an interesting topic in the research field of surface enhanced Raman scattering (SERS). In this work, the selective PDSC reactions of p,p’-dimercaptoazobenzene (DMAB) produced from para-aminothiophenol (PATP) or 4-nitrobenzenethiol (4NBT) were demonstrated in the Ag nanowires dimer-Au film systems. The different SERS spectra collected at individual part and adjacent part of the same nanowire-film system pointed out the importance of the electromagnetic field redistribution induced by image charge on film in this selective surface catalysis, which was confirmed by the simulated electromagnetic simulated electro- magnetic field distributions. Our result indicated this electromagnetic field redistribution induced selective surface catalysis was largely affected by the polarization and wavelength of incident light but slightly by the difference in diameters between two nanowires. Our work provides a further understanding of PDSC reaction in metal nanostructure and could be a deep support for the researches on surface catalysis and surface analysis.

Metal Nanoparticle–Nanowire Assisted SERS on Film

The electromagnetic field redistribution in metal nanostructure–film systems exhibits great capability of confining light on plain film, which has great significance in surface-enhanced Raman scattering (SERS) of a molecule on plain film or 2D material. In this work, the SERS spectra of a monolayer molecule on metal or dielectric film were investigated with the help of a metal nanoparticle–nanowire structure. The results indicated that SERS intensity from an adjacent nanoparticle was much greater than that from an individual nanowire, which was confirmed by the simulated electric field distribution through finite method. The polarization dependence of both experimental and simulated data pointed out the importance of electromagnetic field redistribution in this phenomenon. Furthermore, the shape independence of a nanoparticle found in this work greatly improved the application prospect of this nanoparticle–nanowire assisted SERS on film.

Electromagnetic field redistribution in coupled plasmonic nanoparticle dimer-dielectric substrate system

Combining simulations and experiments, we demonstrate that the surface enhanced Raman scattering (SERS) system of a metal nanoparticle dimer on a dielectric substrate shows strong electromagnetic field enhancement in the particle/substrate gap because of the electromagnetic field redistribution. Besides, in some configurations, the presence of the substrate makes the strongest field enhancement in the gap between the two nanoparticles (i.e. the dimer) occur at the quadruple resonance, not the dipole resonance as usual. The result is very instructive in the difference between the ideal theoretical systems and the real experimental configuration.

Electromagnetic field redistribution in hybridized plasmonic particle-film system

Combining simulation and experiment, we demonstrate that a metal nanoparticle dimer on a gold film substrate can confine more energy in the particle/film gap because of the hybridization of the dimer resonant lever and the continuous state of the film. The hybridization may even make the electric field enhancement in the dimer/film gap stronger than in the gap between particles. The resonant peak can be tuned by varying the size of the particles and the film thickness. This electromagnetic field redistribution has tremendous applications in sensor, photocatalysis and solar cell, etc., especially considering ultrasensitive detection of tracing molecule on substrates.