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The predominant methods currently used to determine nonlinear optical constants like the nonlinear refractive index n2 or the third order susceptibility χ(3) rely mostly on experimental, open and closed z-scan techniques and beam deflection methods. While these methods work well when the linear absorption is relatively small or negligible, the retrieval process is more complicated for a strongly scattering, dispersive or absorbing medium. The study of optics at the nanoscale in the picosecond or femtosecond laser pulsed regimes demands the development of new theoretical tools, and diverse experimental approaches, to extract and verify both linear and nonlinear optical dispersions exhibited by matter, especially when material constituents are fashioned into nanostructures of arbitrary shape. We present a practical, combined experimental and theoretical approach based on the hydrodynamic model that uses experimental results of harmonic generation conversion efficiencies to retrieve complex, nonlinear dispersion curves, not necessarily only for third order processes. We provide examples for materials that are of special interest to nanophotonics, for example, silicon, gold, and indium tin oxide (ITO), which displays nonlocal effects and a zero-crossing of the real part of the dielectric constant. The results for silicon and gold compare well with analytical predictions of nonlinear dispersion based on the nonlinear oscillator model. Based on our assessment of third harmonic generation conversion efficiencies in silicon, we predict χω(3) and χ3ω(3) are of order 10−17 (m/V)2 in the visible and near IR ranges, with respective peaks of 10−14 (m/V)2 and 10−16 (m/V)2 in the UV range. Similarly, gold’s χω(3) and χ3ω(3) are of order 10−17–10−16 (m/V)2, and predict χω(3)∼10−17(m/V)2 and χ3ω(3)∼10−18(m/V)2 for ITO. These results clearly suggest that judicious exploitation of the nonlinear dispersion of ordinary semiconductors has the potential to transform device physics in spectral regions that extend well into the UV range.

Understanding how light interacts with matter at the nanoscale is pivotal if one is to properly engineer nano-antennas, filters and other devices whose geometrical features approach atomic size. We report experimental results on second and third harmonic generation from 20 nm- and 70 nm-thick gold layers, for TE- and TM-polarized incident light pulses. We discuss the relative roles that bound electrons and an intensity dependent free electron density (hot electrons) play in third harmonic generation. While planar structures are generally the simplest to fabricate, metal layers that are only a few nanometers thick and partially transparent are almost never studied. Yet, transmission offers an additional reference point to compare experimental measurements with theoretical models. Our experimental results are explained well within the context of the microscopic hydrodynamic model that we employ to simulate second and third harmonic conversion efficiencies. Using our experimental observations we estimate ∣ χ 1064 n m ( 3 ) ∣≈ 10 − 18 ( m/V ) 2 , triggered mostly by hot electrons.

The use of semiconductors, metals and conductive oxides in the process of fabrication of actual nano devices is at the front edge of nowadays technology, exploiting the properties of light propagation and localization at nanometric scale in new and surprising ways. At these scales the usual theory describing the nonlinear (NL) effects of electromagnetic fields should be revisited and analyzed. We report a collection of experimental results of nonlinear harmonic generation in different nanolayers: semiconductors, conductive oxides and metals. The comparison of these experimental results with numerical predictions of our theoretical model identifies, distinguishes and explains the different nonlinear contributions to the harmonics generated by these materials at nanoscale. Our model accounts for surface, magnetic and bulk nonlinearities arising from free and bound charges, preserving linear and nonlinear dispersion, nonlocal effects due to pressure and viscosity.

We present an experimental study of second harmonic generation from a 20nm-thick indium tin oxide layer in the proximity of its epsilon-near-zero condition. We report measurements of second harmonic efficiencies as a function of the input wavelength and angle of incidence close to the epsilon-near-zero crossing point. We perform theoretical simulations using a hydrodynamical model that is able to capture all major physical mechanisms driving the nonlinear electrodynamic behaviour of conductive oxides. The experimental and theoretical results are compared and a very good quantitative and qualitative agreement is found.

We report a comparative experimental and theoretical study of second harmonic generation from a 20nm-thick indium tin oxide nanolayer in the proximity of the epsilon-near-zero condition. We record the efficiency of the second harmonic signal both as a function of wavelength as well as of the angle of incidence around the epsilon-near-zero crossing point. We compare our experimental results with numerical simulations based on a hydrodynamical model able to capture all major physical mechanisms driving the electrodynamic behavior of conductive oxide layers, with unique aspects of the different nonlinear sources. We found a very good quantitative and qualitative agreement between experiment and theory.

We discuss a dynamical model of harmonic generation that arises from surfaces that demarcate two different metals or conductors, or the electron cloud that spills outside a simple metal surface and the interior bulk, having different electron densities, for example a noble metal such as gold, and indium tin oxide (ITO). While in general two adjacent materials may contain free and bound charges that determine their respective dielectric constants, the transition region may be characterized by a large discontinuity in the free electron density, , epsilon-near-zero conditions, or multiple, nested plasmonic resonances. For example, , while the free-electron cloud that spills outside a noble metal surface decreases as a function of position from the hard ionic surface. These discrepancies lead to the prediction that the angular dependence of second harmonic generation (SHG) from a simple planar structure is direction-dependent, and highlights the sensitivity of both SHG and third harmonic generation to the makeup of the surface and what surrounds it. Our calculations also suggest that the nonlinear optical analysis of more complicated, hybrid structures, such as metal/oxide nanoantennas or metasurfaces, should always be performed by including effects that are generally overlooked, such as nonlocal effects (viscosity and pressure); the presence of linear and nonlinear quantum tunneling currents in the nano- and sub nano-gaps between the nanoantenna and embedded nanoparticles; linear and nonlinear contributions of bound (inner-core) electrons to the dielectric constant.

The absorption of electromagnetic waves has always attracted a large interest because of its cross-the-board nature that spans from microwave to optical frequencies in both linear and nonlinear regimes. At the same time, the experimental isolation of bi-dimensional (2D) materials has recently unveiled how single layers might also be very attractive because of their unprecedented optical and absorption properties. In particular, graphene, a 2D version of graphite, exhibits a remarkably high absorption value (∼2.3%) in the visible range [1] when compared to metals or dielectric materials. In this paper, we will review and illustrate the quest for the enhanced absorption in photonic nanostructures that incorporate monolayer and multilayer graphene sheets emphasizing the difference in terms of configurations and strategies proposed in literature. Then, we will detail the optical performance of graphene-based one-dimensional (1D) gratings that support guided mode resonances showing how it is possible to tune theoretically and experimentally their total absorption ranging from 2.3% to perfect absorption by means of metallic and dielectric reflectors or engineered super cells.

We present a detailed analysis of the optical properties of one-dimensional arrays of slits in metal films. Although enhanced transmission windows are dominated by Fabry-Perot cavity modes localized inside the slits, the periodicity introduces surface modes that can either enhance or inhibit light transmission. We thus illustrate the interaction between cavity modes and surface modes in both finite and infinite arrays of slits. In particular we study a grating that clearly separates surface plasmon effects from Wood-Rayleigh anomalies. The periodicity of the grating induces a strong plasmonic band gap that inhibits coupling to the cavity modes for frequencies near the center of the band gap, thereby reducing the transmission of the grating. Strong field localization at the high energy plasmonic band edge enhances coupling to the cavity modes while field localization at the low energy band edge leads to weak cavity coupling and reduced transmission.

Extraordinary transmission through thick gratings results from resonances inside the apertures and is narrowband. We report observation of extremely broadband transmission through thick gratings at angles of incidence related to a Brewster angle.

We theoretically investigate second harmonic generation that originates from the nonlinear, magnetic Lorentz force term from single and multiple apertures carved on thick, opaque metal substrates. The linear transmission properties of apertures on metal substrates have been previously studied in the context of the extraordinary transmission of light. The transmission process is driven by a number of physical mechanisms, whose characteristics and relative importance depend on the thickness of the metallic substrate, slit size, and slit separation. In this work we show that a combination of cavity effects and surface plasmon generation gives rise to enhanced second harmonic generation in the regime of extraordinary transmittance of the pump field. We have studied both forward and backward second harmonic generation conversion efficiencies as functions of the geometrical parameters, and how they relate to pump transmission efficiency. The resonance phenomenon is evident in the generated second harmonic signal, as conversion efficiency depends on the duration of incident pump pulse, and hence its bandwidth. Our results show that the excitation of tightly confined modes as well as the combination of enhanced transmission and nonlinear processes can lead to several potential new applications such as photo-lithography, scanning microscopy, and high-density optical data storage devices., Keywords: Enhanced Transmission, Second Harmonic Generation, Surface Plasmon, Sub-wavelength Slit

We are designing and fabricating arrays of subwavelength SP structures in metal films and combining these structures with EO polymers to understand the interaction of the EO polymer with the enhanced electric fields of the plasmons. We have designed and modeled resonance structures to maximize extraordinary transmittance. We are making a systematic study of SP structure shapes by studying circular holes, elliptical holes and slits. Initially we have fabricated and begun optical evaluation of subwavelength slits in gold films. Slits with 32 nm width and 120 nm width have been fabricated by a focused ion beam system. Preliminary optical transmittance measurements in the visible and NIR are underway and will be compared to theoretical modeling.

Summary form only given. Negative refraction and sub-wavelength imaging in the visible part of the spectrum are numericlly investigated using a multilayer, metal-dielectric photonic band gap structure. Results show that the main underlying physical mechanism for sub-wavelength focusing comes as a result of resonance tunneling, field localization and propagation effects, and that surface plasmons do not play a significant role. The advantage of these structures is that both tunability and high transmission are achievable across the visible wavelength regime as well as into the infrared regime.

We proposed a coherent source based on parametric down-conversion in a photonic crystal. Our design is based on the band edge or defect-mode field enhancement phenomena near a photonic band gap. The numerical results show that a range of bandwidths, intensities, and frequencies up to 12 THz can be obtained.

International Quantum Electronics Conference 2004, San Francisco, California United States, 16–21 May 2004, We propose a device based on a one-dimensional photonic band gap structure that is optimized for the generation of coherent, THz radiation tunable up to 10 THz.

We report theoretical predictions and experimental results on the formation of pass bands and stop bands of extraordinary acoustic transmission in multilayer structures based on alternating layers of acoustic metamaterial and air. The metamaterial layers can be made of any acoustically hard material perforated with a two-dimensional array of subwavelength apertures. In this way, it is possible to tailor the density and speed of sound of an otherwise acoustically bulk hard material with fixed properties. The sonic band structure allows transmission passband and stop bandgaps that depend on the layer thicknesses and effective properties of the metamaterials. In addition, we show the existence of resonant tunneling due to the formation of an acoustic passband in a spectral region of low transmission for a single layer. This opens the possibility to engineer different types of phononic materials to manipulate and control acoustic waves.

We exploit the metamaterial properties of a thick metallic grating with extreme sub-wavelength slits on a metallic slab to achieve complete absorption of transverse magnetic polarized microwaves. We measure narrow bands of total absorption (up to 99.9999%) from normal to grazing incidence that can be tuned by varying an air gap between the grating and the slab. Unlike typical absorbers, the structure is mostly metallic with a 97% filling factor, and no absorptive material beside the metal itself is employed. We access the absorption properties of metals in the microwave where they are commonly believed to be perfect reflectors.

We demonstrate experimentally the existence of an omnidirectional reflection band of a two-dimensional metamaterial structure consisting of split ring resonators and thin conducting wires. Experimental angular reflectance data agree reasonably well with simulations using model dispersion relations for the effective dielectric permittivity and magnetic permeability that were fitted to the experimentally retrieved material parameters. The tunability of the reflection bandwidth is demonstrated by changing the effective electric plasma frequency. These findings are also relevant to optical frequencies where similar metamaterial composites have been fabricated.

The authors present a theoretical analysis of a super-resolving lens based on one-dimensional metal-dielectric photonic band gap composed of Ag∕GaP multilayers. The lens contains a total of ten optical skin depths of Ag, yet maintains a normal incidence transmittance of ∼50% for propagating waves over the super-resolving wavelength range of 500–650nm. The individual Ag layers are 22nm thick and can be readily fabricated in conventional deposition systems. The importance of antireflection coatings for the transmission of evanescent and propagating waves is illustrated by comparison to periodic and symmetric structures without the coatings.

In this paper we describe a way to achieve the extraordinary transmission regime from sub-wavelength slits carved on semiconductor substrates. Unlike metals, the dielectric permittivity of typical semiconductors like GaAs or GaP is negative beginning in the extreme UV range (lambda

We proposed a coherent source based on parametric down-conversion in a photonic crystal. Our design is based on the band edge or defect-mode field enhancement phenomena near a photonic band gap. The numerical results show that a range of bandwidths, intensities, and frequencies up to 12 THz can be obtained.

In this paper we describe a way to achieve the extraordinary transmission regime from sub-wavelength slits carved on semiconductor substrates. Unlike metals, the dielectric permittivity of typical semiconductors like GaAs or GaP is negative beginning in the extreme UV range (lambda