arXiv subjects

M. J. Bloemer

Publications and source records attributed to M. J. Bloemer.

12 recordsLinked to original sources

arXiv2018

Harmonic Generation from Metal-Oxide and Metal-Metal Boundaries

We explore the outcomes of detailed microscopic models by calculating second- and third-harmonic generation from thin film surfaces with discontinuous free-electron densities. These circumstances can occur in structures consisting of a simple metal mirror, or arrangements composed of either different metals or a metal and a free electron system like a conducting oxide. Using a hydrodynamic approach we highlight the case of a gold mirror, and that of a two-layer system containing indium tin oxide (ITO) and gold. We assume the gold mirror surface is characterized by a free-electron cloud of varying density that spills into the vacuum, which as a result of material dispersion exhibits epsilon-near-zero conditions and local field enhancement at the surface. For a bylayer consisting of a thin ITO and gold films, if the wave is incident from the ITO side the electromagnetic field is presented with a free-electron discontinuity at the ITO/gold interface, and wavelength-dependent, epsilon-near-zero conditions that enhance local fields and conversion efficiencies, and determine the surface's emission properties. We evaluate the relative significance of additional nonlinear sources that arise when a free-electron discontinuity is present, and show that harmonic generation can be sensitive to the density of the screening free-electron cloud, and not its thickness. Our findings also suggest the possibility to control surface harmonic generation through surface charge engineering.

physics.optics↗

arXiv2018

Reevaluation of radiation reaction and consequences for light-matter interactions at the nanoscale

In the context of electromagnetism and nonlinear optical interactions damping is generally introduced as a phenomenological, viscous term that dissipates energy, proportional to the temporal derivative of the polarization. Here, we follow the radiation reaction method presented in [G. W. Ford and R. F. O'Connell, Phys. Lett. A, 157, 217 (1991)], which applies to non-relativistic electrons of finite size, to introduce an explicit reaction force in the Newtonian equation of motion, and derive a hydrodynamic equation that offers new insight on the influence of damping in generic plasmas, metal-based and/or dielectric structures. In these settings, we find new damping-dependent linear and nonlinear source terms that suggest the damping coefficient is proportional to the local charge density, and nonlocal contributions that stem from the spatial derivative of the magnetic field and discuss the conditions that could modify both linear and nonlinear electromagnetic responses.

physics.optics↗

arXiv2011

A Dynamical Model of Harmonic Generation in Centrosymmetric Semiconductors

We study second and third harmonic generation in centrosymmetric semiconductors at visible and UV wavelengths in bulk and cavity environments. Second harmonic generation is due to a combination of symmetry breaking, the magnetic portion of the Lorentz force, and quadrupolar contributions that impart peculiar features to the angular dependence of the generated signals, in analogy to what occurs in metals. The material is assumed to have a non-zero, third order nonlinearity that gives rise to most of the third harmonic signal. Using the parameters of bulk Silicon we predict that cavity environments can significantly modify second harmonic generation (390nm) with dramatic improvements for third harmonic generation (266nm). This occurs despite the fact that the harmonics may be tuned to a wavelength range where the dielectric function of the material is negative: a phase locking mechanism binds the pump to the generated signals and inhibits their absorption. These results point the way to novel uses and flexibility of materials like Silicon as nonlinear media in the visible and UV ranges.

physics.optics↗

arXiv2010

The nature of transmission resonances in plasmonic metallic gratings

Using the Fourier modal method (FMM) we report our analysis of the transmission resonances of a plasmonic grating with sub-wavelength period and extremely narrow slits for wavelengths of the incoming, transverse magnetic (TM)-polarized, radiation ranging from 240nm to 1500nm and incident angles from 0 degree to 90 degree. In particular, we study the case of a silver grating placed in vacuo. Consistent with previous studies on the topic, we highlight that the main mechanism for extraordinary transmission is a TM-Fabry-Perot (FP) branch supported by waveguide modes inside each slit. The TM-FP branch may also interact with surface plasmons (SPs) at the air/Ag interface through the reciprocal lattice vectors of the grating, for periods comparable with the incoming wavelength. When the TM-FP branch crosses a SP branch, a band gap is formed along the line of the SP dispersion. The gap has a Fano-Feshbach resonance at the low frequency band edge and a ridge resonance with extremely long lifetime at the high frequency band edge. We discuss the nature of these dispersion features, and in particular we describe the ridge resonance in the framework of guided-mode resonances (GMRs). In addition, we elucidate the connection of the coupling between the TM-FP branch and SPs within the Rayleigh condition. We also study the peculiar characteristics of the field localization and the energy transport in two topical examples.

physics.optics↗

arXiv2010

Enhancement and Inhibition of Transmission from metal gratings: Engineering the Spectral Response

We present a systematic analysis of the optical properties of slit arrays in metal films. An exhaustive investigation of geometrical and dispersive properties reveals the resonance features of these structures, including the role of surface waves and their relationship with features in the transmission spectrum. Although enhanced transmission windows are significantly dominated by the longitudinal resonances localized inside the slits, the periodicity introduces transverse resonances that can either enhance or inhibit light transmission. We thus illustrate the intriguing interaction regime between longitudinal and transverse resonances, where the two modes hybridize leading to the formation of a photonic band gap spectrum.

physics.optics↗

arXiv2010

Second and Third Harmonic Generation in Metal-Based Nanostructures

We present a new theoretical approach to the study of second and third harmonic generation from metallic nanostructures and nanocavities filled with a nonlinear material, in the ultrashort pulse regime. We model the metal as a two-component medium, using the hydrodynamic model to describe free electrons, and Lorentz oscillators to account for core electron contributions to both the linear dielectric constant and to harmonic generation. The active nonlinear medium that may fill a metallic nanocavity, or be positioned between metallic layers in a stack, is also modeled using Lorentz oscillators and surface phenomena due to symmetry breaking are taken into account. We study the effects of incident TE- and TM-polarized fields and show that a simple re-examination of the basic equations reveals additional exploitable dynamical features of nonlinear frequency conversion in plasmonic nanostructures.

physics.optics↗

arXiv2009

Extraordinary Transmission in the UV Range from Sub-wavelength Slits on Semiconductors

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 <= 270nm). We show that the metal-like response of bulk semiconductors exhibits surface plasmon waves that lead to extraordinary transmission in the UV and soft X-ray ranges. The importance of realistic material response versus perfect conductors is also discussed. These findings may be important in high resolution photo-lithography, near field optical devices and ultra high density optical storage.

physics.optics↗

arXiv2009

Bloch vector analysis in non linear, finite, dissipative systems: an experimental study

We have investigated and experimentally proved the robustness of the Bloch vector for one-dimensional, nonlinear, finite, dissipative systems. The case studied is the second harmonic generation from metallo-dielectric filters. Nowadays metallic based nanostructures play a fundamental role in nonlinear nano-photonics and nano-plasmonics. Our results clearly suggest that even in these forefront fields the Bloch vector continues to play an essential role.

physics.optics↗

arXiv2009

Extraordinary nonlinear optics in ordinary semiconductors

We numerically demonstrate inhibition of absorption, optical transparency, and anomalous momentum states of phase locked harmonic pulses in semiconductors, at UV and extreme UV frequencies, in spectral regions where the dielectric constant of typical semiconductors is negative. We show that a generated harmonic signal can propagate through a bulk metallic medium without being absorbed as a result of a phase locking mechanism between the pump and its harmonics. These findings may open new regimes in nonlinear optics and are particularly relevant to the emerging fields of nonlinear negative index meta-materials and nano-plasmonics, especially in the ultrafast pulse regime.

physics.optics↗

arXiv2008

Semiconductor-based superlens for sub-wavelength resolution below the dif-fraction limit at extreme ultraviolet frequencies

We theoretically demonstrate negative refraction and sub-wavelength resolution below the diffraction limit in the UV and extreme UV ranges using semiconductors. The metal-like re-sponse of typical semiconductors such as GaAs or GaP makes it possible to achieve negative refraction and super-guiding in resonant semiconductor/dielectric multilayer stacks, similar to what has been demonstrated in metallo-dielectric photonic band gap structures. The exploita-tion of this basic property in semiconductors raises the possibility of new, yet-untapped ap-plications in the UV and soft x-ray ranges.

physics.optics↗

arXiv2008

Second harmonic generation from metallo-dielectric multilayer photonic band gap structures

We experimentally and theoretically investigate the second order nonlinear optical response of metallo-dielectric multilayer structures composed of Ag and Ta2O5 layers, deposited by magnetron sputtering. Second harmonic generation measurements were performed in reflection mode as a function of incidence angle, using femtosecond pulses originating from a Ti:Sapphire laser system tuned at 800 nm. The dependence of the generated signal was investigated as a function of pump intensity and polarization state. Our experimental results show that the conversion efficiency from a periodic metallo-dielectric sample may be enhanced by at least a factor of 30 with respect to the conversion efficiency from a single metal layer, thanks in part to the increased number of active surfaces, pump field localization and penetration inside the metal layers. The conversion efficiency maximum shifts from 70 degrees for the single silver layer down to approximately 55 degrees for the stack. The experimental results are found to be in good agreement with calculations based on coupled Maxwell-Drude oscillators under the action of a nonlinear Lorentz force term.

physics.optics↗

arXiv2008

Tailoring Metallodielectric Structures for Super Resolution and Superguiding Applications in the Visible and Near IR Ranges

We discuss propagation effects in realistic, transparent, metallo-dielectric photonic band gap structures in the context of negative refraction and super-resolution in the visible and near infrared ranges. In the resonance tunneling regime, we find that for transverse-magnetic incident polarization, field localization effects contribute to a waveguiding phenomenon that makes it possible for the light to remain confined within a small fraction of a wavelength, without any transverse boundaries, due to the suppression of diffraction. This effect is related to negative refraction of the Poynting vector inside each metal layer, balanced by normal refraction inside the adjacent dielectric layer: The degree of field localization and material dispersion together determine the total momentum that resides within any given layer, and thus the direction of energy flow. We find that the transport of evanescent wave vectors is mediated by the excitation of quasi-stationary, low group velocity surface waves responsible for relatively large losses. As representative examples we consider transparent metallo-dielectric stacks such as Ag/TiO2 and Ag/GaP and show in detail how to obtain the optimum conditions for high transmittance of both propagating and evanescent modes for super-guiding and super resolution applications across the visible and near IR ranges. Finally, we study the influence of gain on super-resolution. We find that the introduction of gain can compensate the losses caused by the excitation of surface plasmons, improves the resolving characteristics of the lens, and leads to gain-tunable super-resolution.

physics.optics↗