arXiv subjects

Mark J. Bloemer

Publications and source records attributed to Mark J. Bloemer.

10 recordsLinked to original sources

arXiv2009

Transmission function properties for multi-layered structures: Application to super-resolution

We discuss the properties of the transmission function in the k-space for a generic multi-layered structure. In particular we analytically demonstrate that a transmission greater than one in the evanescent spectrum (amplification of the evanescent modes) can be directly linked to the guided modes supported by the structure. Moreover we show that the slope of the phase of the transmission function in the propagating spectrum is inversely proportional to the ability of the structure to compensate the diffraction of the propagating modes. We apply these findings to discuss several examples where super-resolution is achieved thanks to the simultaneous availability of the amplification of the evanescent modes and the diffraction compensation of the propagating modes.

physics.optics↗

arXiv2008

Homogenization procedure for a metamaterial and local violation of the second principle of thermodynamics

Classical theory of crystals states that a medium to be considered homogeneous must satisfy the following requirements: a) the dimension of the elementary cell must be much smaller than the incident wavelength; b) the sample must contain a large number of elementary cells, i.e. it must be macroscopic with respect to wavelength. Under these conditions, macroscopic quantities can be introduced in order to describe the optical response of the medium. We analytically demonstrate that for a symmetric elementary cell those requirements can be relaxed, and it is possible to assign a permittivity and a permeability to a composite structure, even if the metamaterial cannot be considered homogeneous under the requirements stated above. However, the effective permittivity and permeability in some cases may give rise to unphysical, effective behaviors inside the medium, notwithstanding the fact that they satisfy requirements like being Kramers-Kronig pairs, for example, and are consistent with all the linear properties outside the structure (i.e. reflection, transmission, and absorption at all frequencies). In some situations the medium is assigned a magnetic response even though the medium is not magnetically active. In particular, we demonstrate that the homogenization procedure can lead to a medium that locally violates the second principle of thermodynamics. We also show that, in the non-homogeneous regime, it is not possible to describe the nonlinear behavior of the structure using an effective parameters approach, despite the possibility to assign an effective linear refractive index.

physics.optics↗

arXiv2008

On the Inhibition of Linear Absorption in Opaque Materials Using Phase-Locked Harmonic Generation

We theoretically predict and experimentally demonstrate inhibition of linear absorption for phase and group velocity mismatched second and third harmonic generation in strongly absorbing materials, GaAs in particular, at frequencies above the absorption edge. A 100-fs pump pulse tuned to 1300nm generates 650nm and 435nm second and third harmonic pulses that propagate across a 450 micron-thick GaAs substrate without being absorbed. We attribute this to a phase-locking mechanism that causes the pump to trap the harmonics and to impress them with its dispersive properties.

physics.optics↗

arXiv2008

Influence of the losses on the super-resolution performances of an impedance matched negative index material

We discuss by a Poynting vector analysis how the losses of a negative index material (NIM) affect the resolution performances of a Veselago-Pendry lens and we analyze those performances in the framework of the Abbe criterion. Both the limit of high losses and low losses are explored. We find that the impedance matched NIM is able to resolve 30% better than the limit imposed by the Abbe criterion even when the imaginary part of the refractive index (the material losses) exceeds the absolute value of the real part of the refractive index. The NIM is described by a lossy Drude model with equal permittivity and permeability. By increasing the damping parameter of the Drude model we also explore the regime where both permittivity and permeability are positive and point out the conditions under which the metamaterial is still able to super-resolve.

physics.optics↗

arXiv2008

Ultra-slow light pulses in a nonlinear metamaterial

We find the analytical expression for the threshold intensity necessary to launch ultra-slow light pulses in a metamaterial with simultaneous cubic electric and magnetic nonlinearity. The role played respectively by the permittivity, the permeability, the electric cubic nonlinearity, the magnetic cubic nonlinearity and the pulse duration is clearly identified and discussed.

physics.optics↗

arXiv2008

Anomalous Momentum States, Non-Specular Reflections, and Negative Refraction of Phase-Locked, Second Harmonic Pulses

We simulate and discuss novel spatio-temporal propagation effects that relate specifically to pulsed, phase-mismatched second harmonic generation in a negative index material having finite length. Using a generic Drude model for the dielectric permittivity and magnetic permeability, the fundamental and second harmonic frequencies are tuned so that the respective indices of refraction are negative for the pump and positive for the second harmonic signal. A phase-locking mechanism causes part of the second harmonic signal generated at the entry surface to become trapped and dragged along by the pump and to refract negatively, even though the index of refraction at the second harmonic frequency is positive. These circumstances culminate in the creation of an anomalous state consisting of a forward-moving second harmonic wave packet that has negative wave vector and momentum density, which in turn leads to non-specular reflections at intervening material interfaces. The forward-generated second harmonic signal trapped under the pump pulse propagates forward, but has all the attributes of a reflected pulse, similar to its twin counterpart generated at the surface and freely propagating backward away from the interface. This describes a new state of negative refraction, associated with nonlinear frequency conversion and parametric processes, whereby a beam generated at the interface can refract negatively even though the index of refraction at that wavelength is positive.

physics.optics↗

arXiv2006

Broadband superresolving lens with high transparency for propagating and evanescent waves in the visible range

We present a theoretical analysis of a super-resolving lens based on 1-dimensional metallo-dielectric photonic crystals composed of Ag/GaP multilayers. The lens contains a total of 10 optical skin depths of Ag, yet maintains a normal incidence transmittance of ~50% for propagating waves over the super-resolving wavelength range of 500-650 nm. The individual Ag layers are 22 nm thick and can be readily fabricated in conventional deposition systems. The importance of anti-reflection coatings for the transmission of evanescent and propagating waves is illustrated by comparison to periodic and symmetric structures without the coatings. In addition, the reflection for propagating waves is reduced to ~5% across the super-resolving wavelength band diminishing the interference between the object and the lens.

physics.optics↗

arXiv2006

Enhancement and Inhibition of Stimulated Processes in a Negative Index Cavity

We study second harmonic generation in a negative index material cavity. The transmission spectrum shows a gap between the electric and magnetic plasma frequencies, so that localized and anti-localized states are allowed at the band edges. The process is made efficient by local phase matching conditions between a forward-propagating pump and a backward-propagating second harmonic signal. By simultaneously exciting the cavity with counter-propagating pulses one is able to enhance or inhibit absorption and stimulated processes. The control parameter is the relative phase difference between the two incident pulses which determines the interference properties of the fields inside the cavity.

physics.optics↗

arXiv2006

Analysis of second harmonic generation in photonic-crystal-assisted waveguides

We study second harmonic generation in a planar dielectric waveguide having a low-index, polymer core layer, bounded by two multilayer stacks. This geometry allows exceptionally strong confinement of the light at the fundamental wavelength inside the core region with virtually zero net propagation losses for distances that exceed several centimeters, provided material and scattering losses are neglected. A phase-matched configuration of the waveguide is reported in which the pump signal is the lowest-order mode of the waveguide, and the generated second harmonic signal corresponds to the third propagation mode of the waveguide. Using a polymer waveguide core, having chi(2)=100 pm/V, we predict a conversion efficiency of approximately 90% after a propagation distance of 2 mm, using peak pump intensities inside the core of the waveguide of 1.35 GW/cm^2. If the waveguide core contains polymer layers with different glass transition temperatures, the layers can be poled independently to maximize the overlap integral, and similar pump depletions may be achieved over a distance of approximately 500 microns.

physics.optics↗

arXiv2006

Negative refraction and sub-wavelength imaging using transparent metal-dielectric stacks

Negative refraction is known to occur in materials that simultaneously possess a negative electric permittivity and magnetic permeability; hence they are termed negative index materials. However, there are no known natural materials that exhibit a negative index of refraction. In large part, interest in these materials is due to speculation that they could be used as perfect lenses with superresolution. We propose a new way of achieving negative refraction with currently available technology, based on transparent, metallo-dielectric multilayer structures. The advantage of these structures is that both tunability and transmission (well above 50%) can be achieved in the visible wavelength regime. We demonstrate both negative refraction and superresolution in these structures. Our findings point to a simpler way to fabricate a material that exhibits negative refraction. This opens up an entirely new path not only for negative refraction, but also to expand the exploration of wave propagation effects in metals.

physics.optics↗