A plasma frequency modulation model for constructing structure material with arbitrary cross-section thin metallic wires

Considering the fact that just the electrons confined in the region of the skin depth will actually affect the plasma frequency due to the skin effect, a model for constructing epsilon-near-zero (ENZ) metamaterials through the arranged thin metallic wires with arbitrary cross-section is developed, utilizing the perimeter approximation. With our model, plasma frequency can be freely modulated just by the variance of the metallic wire perimeter, irrespective of the cross-section shape of wires. The finite element method (FEM) and S-parameters retrieval method were employed to numerically simulate the plasma frequencies, which have verified the validity of the theoretical model.     

Influence of a magnetically permeable surface layer on transient fields for a thin circular loop antenna

The transient fields, in the time-domain, of a thin circular loop antenna, on a two-layered earth’s model are reexamined when the usually neglected magnetic permeability contrast is considered. It is shown that for a two-layered earth model, where the upper layer is permeable, the transient fields are modified over the nonpermeable case. The fields in the time domain are obtained as the inverse Laplace transforms of derived full wave time-harmonic solution. These time-domain solutions are obtained as a summation of waveguide modes plus contributions from branch cuts in the complex plane of the longitudinal wave number. The results should be useful for interpreting airborne electromagnetic systems and in cases where super-paramagnetic mineral constant is present.     

Influence of a magnetically permeable surface layer on transient electromagnetic field of a vertical magnetic dipole on a two-layer conducting earth

The transient electromagnetic field, in the frequency domain, on a two-layered conducting earth is reexamined when the usually neglected magnetic permeability contrast is considered. It is shown that for two-layered earth model, where the upper is permeable, the electromagnetic induction response is modified over the nonpermeable case. It is obtained as a summation of waveguide modes plus contributions from branch-cuts in the complex plane of the longitudinal wave number. The results from this paper can be used to evaluate numerical solution of other more complicated forward modeling algorithms. It can also be used in developing fast and simple interpretation tools, which can deliver quick estimation of the earth structure at the field.     

Ultrafast dynamics of surface electromagnetic waves in nanohole array on metallic film

We study the ultrafast dynamics of surface electromagnetic waves photogenerated on aluminum film perforated with subwavelength holes array by means of transient photomodulation with ∼100 fs time resolution. We observed a pronounced blueshift of the resonant transmission band that reveals the important role of plasma attenuation in the dynamics and that is inconsistent with plasmon–polariton mechanism of extraordinary transmission. The transient photomodulation spectra were successfully modeled within the Boltzmann equation approach for the electron–phonon relaxation dynamics, involving non-equilibrium hot electrons and quasi-equilibrium phonons.     

Positively and negatively large Goos–Hänchen lateral displacements from a symmetric gyrotropic slab

A detailed study on the lateral displacements of a transverse magnetic (TM) wave transmitted and reflected from a symmetric gyrotropic slab is presented. We give the analytic formulas for the transmission coefficient and the reflection coefficient, as well as the corresponding lateral displacements. It is found that due to the external magnetic field the displacement of a transmitted beam is different from that of reflected one, even for a lossless symmetric configuration. Furthermore, within the chosen frequency band, when the incident angle is near the Brewster angle, the shift of a reflected wave can be large with nonzero reflectance, and can be positive or negative depending on the direction of the applied magnetic field and the incident wave.     

Compact optical filter for dual-wavelength fluorescence-spectrometry based on enhanced transmission through metallic nano-slit array

A novel optical filter based on enhanced transmission through metallic nano-slit is proposed for dual-wavelength fluorescence-spectrometry. A special structure, sampled-period slit array, is utilized to meet the requirement of dual-wavelength transmission in this system. Structure parameters on the transmission property are analyzed by means of Fourier transformation. With the features both to enhance the fluorescence generation and to enhance light transmission, in addition with the feasibility for miniaturization, integration on one chip, and mass production, the proposed filters are promising for the realization of dual-wavelength fluorescence-spectrometry in micro-total-analysis-system.     

Fringe waves radiated by a half-plane for the boundary conditions of Neumann

The fringe waves of the physical theory of diffraction are obtained in terms of Fresnel integrals for a half-plane satisfying the Neumann boundary condition. The approximate expressions of the radiated waves are also evaluated for sufficiently large wavenumbers. The fields are plotted and compared numerically.     

Highly collimated emission from a left-handed photonic crystal with a quasi-cavity

We study the collimated emission characteristics from a dipole source inside a negative-effective-refractive-index photonic crystal with a quasi-cavity constructed by a concave photonic crystal reflector. The emissions along the ±X and −Y directions are forbidden by the quasi-cavity, so that most emissions propagate along the +Y direction. Simulation results show that a narrow collimated beam is achieved due to the near-zero negative effective refractive index. Moreover, the half-power beam width of such a collimated beam can be reduced to 3.48° by optimizing the size of the source area. Such a compact structure would have potential applications in micro-optical devices.     

Considerations about Z-scan sensitivity improvement: theory versus experiments

This paper reports an experimental demonstration of the improvement of the Z-scan technique’s sensitivity. It is shown that this sensitivity can be multiplied by a factor equal to almost 400 with the help of simple binary diffractive elements. Such a possibility was actually predicted theoretically in one of our previous papers. In this study, the interpretation is investigated in a wider context taking into account the definition of the signal normalisation as introduced by Z-scan and the well-known eclipsing Z-scan (EZ-scan) experiments. In particular, advantages and drawbacks are compared, by looking at the normalised or the unnormalised aperture transmission.     

Propagation oscillations in the near-field response of traveling surface waves launched by metallic nanoapertures

We discuss the implications of a frequency-dependent complex dielectric function ε(ω) of a metal for the interpretation of scanning near-field optical microscopy (SNOM) measurements in the vicinity of metallic nanoapertures. For subwavelength slits in gold films we observe distinct spatial intensity oscillations in the near-field signal for specific wavelengths in the visible spectrum. These oscillations of the SNOM signal far away from the nanoslit are ascribed to a constructive interference between the propagating surface plasmon (SP) with light scattered parallel to the gold–air interface. In these spatial SNOM-signal oscillations information about the surface plasmon dielectric function is encoded which can be extracted, for example, in surface plasmon interferometry for applications as sensors or waveguides.     

Filamentation of ultrashort light pulses in a liquid scattering medium

We have studied filamentation of 1-ps laser pulses in a scattering medium (aqueous suspension of 2-μm polystyrene microspheres) and compared filamentation dynamics to that in pure water. Our results indicate that light scattering does not alter filamentation dynamics in general, but rather results in farther position of the nonlinear focus, shorter filament length, and the development of speckle structure in the peripheral part of the beam. The experimental observations are qualitatively reproduced by the numerical model which accounts for diffraction, self-focusing, multiphoton absorption, and light scattering introduced through a stochastic diffusion and diffraction term.     

Illustration of a bimodal system in Intralipid-20% by polarized light scattering: experiments and modeling

Intralipid suspensions behave like phantoms of human tissues concerning their light scattering properties. We present experimental measurements of the angular distribution of polarized light scattering at various incidence angles on Intralipid-20%. A comparison of the absolute values of these measurements with simulations using a vector radiative transfer model (N-flux) developed for multilayered media demonstrates a stratified structure of the samples with a double distribution of the size of scatterers. This result is confirmed by polarimetry imaging.     

Angular spread of Gaussian Schell-model array beams propagating through atmospheric turbulence

The closed-form expression for the angular spread of Gaussian Schell-model (GSM) array beams propagating through atmospheric turbulence is derived. It is shown that the angular spread θ _sp of GSM array beams for the superposition of the cross-spectral density function is smaller than of those for the superposition of the intensity. However, the θ _sp of GSM array beams for the superposition of the intensity is less sensitive to turbulence than that for the superposition of the cross-spectral density function. For the superposition of the cross-spectral density function, θ _sp of GSM array beams with smaller coherence length σ ₀, smaller waist width w ₀, smaller beam number N, and larger separation distance x _d are less affected by turbulence than of those with larger σ ₀,w ₀,N, and smaller x _d ; while, for the superposition of the intensity, the effect of turbulence on θ _sp is independent of N and x _d . In addition, the angular spread is nearly the same for the two types of superposition when σ ₀ or w ₀ is small enough, or x _d is large enough. On the other hand, it is found that there exist equivalent GSM array beams for the two types of superposition which may have the same directionality as the corresponding fully coherent Gaussian beam in free space and also in turbulence.     

Intensity-driven,laser induced transformation of Ag nanospheres to anisotropic shapes

The shapes of initially spherical Ag nanoparticles in soda-lime glass are persistently changed using fs laser irradiation. With linearly polarized pulses, this shape transformation of the nanoparticles causes optical dichroism of the material. The intensity dependence of this effect is studied comprehensively, addressing the whole intensity range of permanent modifications as well as the influence of the number of laser pulses applied to one spot on the sample. The results are used as basis to develop a complete scenario of the possible mechanisms leading to the laser-induced shape transformation of metallic nanoparticles in glass.     

Comparison of gold and silver dispersion laws suitable for FDTD simulations

We report optical planar waveguide formation and modal characterization in β-BaB₂O₄ crystals by Cu²⁺-ion implantation at an energy of 3.0 MeV and doses of ∼ 10¹⁴ ions/cm². The prism-coupling method was used to investigate the dark-mode property at wavelengths of 633 nm and 1539 nm. The refractive-index profile of the waveguide was reconstructed by an effective refractive index method. The modal analysis indicates that the fields of TM modes can be well restricted in the guiding region, which means the formation of a non-leaky waveguide in the crystal. The results show that the β-BaB₂O₄ waveguides may be used in the application of high efficiency frequency conversion. PACS 61.80.Jh; 42.70.Mp; 42.65.Wi     

Manipulating light flow with one-dimensional photonic crystals of an electromagnetically induced transparency medium

The band structures and equifrequency contours of one-dimensional photonic crystals (PCs), which consist of an electromagnetically induced transparency (EIT) medium and a common dielectric medium, can be dramatically changed by tuning the coupling field intensity (or coupling Rabi frequency, CRF) of the EIT medium. It is found that for a probe light at a fixed frequency, either positive or negative refraction in the EIT PC can be realized with a proper CRF. The behavior of a Gaussian beam (probe light) obliquely incident on such an EIT PC slab is simulated numerically. The probe light beam transmitted from the slab can be shifted transversely in a large range, and negative refraction enhances this effect. The present scenario can be applied in some areas such as quantum optical and photonic device designs.     

Volume structuring of high power LED encapsulates by femtosecond laser direct writing

We report on the micro-fabrication of diffractive optical elements (DOEs) such as 1D, 2D and concentric grating structures inside the volume of thin silicone films by femtosecond laser direct writing. In addition, we show that such structures can also be integrated into silicone films that act as encapsulation layers of high power light-emitting diodes. The latter strategy opens new possibilities to homogenize and to control the light emitted from such devices.     

Laser nano-fabrication of large-area plasmonic structures and surface plasmon resonance tuning by thermal effect

A simple and flexible technique aimed to generate large-area periodic nano-dot array features on metal thin films by laser interference lithography (LIL) has been demonstrated. In this paper, gold nano-dot arrays with a period of ∼450 nm and a dot diameter of ∼100 nm on quartz substrates coated with a gold film of 50 nm thick were fabricated. Multiple enhanced transmission peaks were observed in this patterned film. In addition to the characteristic peak of the gold surface plasmon resonance around 500 nm, multiple shoulder peaks that range from 550 to 700 nm were also observed in the nano-chain array structures. These shoulder peaks disappeared after thermal annealing. It was found that the nano-dots became smaller and well-separated nano-balls under the high temperature annealing process. These nano-structures have potential applications in solar cell, nano-lithography and biosensing.     

Propagation of a stochastic electromagnetic Gaussian Schell-model beam through an optical system in turbulent atmosphere

A generalized diffraction integral formula for stochastic electromagnetic beams propagating through an optical system in turbulent atmosphere is derived with the help of tensor method. Some analyses are illustrated by a numerical example relating to changes in the average intensity and the degree of polarization of an electromagnetic Gaussian Schell-model beam propagating through a double-lenses system. It is shown that the optical system has strong influence on the propagation properties of the beam. The method used in this paper can be widely applied to the propagation of astigmatic beams through an optical system in turbulent atmosphere.