545 research outputs found
Influence of Photoexcitation Depth on Luminescence Spectra of Bulk GaAs Single Crystals and Defect Structure Characterization
The results of investigation of bulk GaAs photoluminescence are presented
taken from near-surface layers of different thicknesses using for excitation
the light with the wavelengths which are close but some greater than the
excitonic absorption resonances (so-called bulk photoexcitation). Only the
excitonic and band-edge luminescence is seen under the interband excitation,
while under the bulk excitation, the spectra are much more informative. The
interband excited spectra of all the samples investigated in the present work
are practically identical, whereas the bulk excited PL spectra are different
for different samples and excitation depths and provide the information on the
deep-level point defect composition of the bulk materials.Comment: Aalborg Summer School on Nonlinear Optics, Aalborg, Denmark, 7-12
August 199
Light controlled photon tunneling
Recent measurements of photon tunneling through individual subwavelength
pinholes in a gold film covered with a layer of polydiacetylene (Phys. Rev.
Letters 88, 187402 (2002)) provided strong indication of "photon blockade"
effect similar to Coulomb blockade phenomenon observed in single-electron
tunneling experiments. Here we report first observation of photon tunneling
been blocked (gated) by light at a different wavelength. This observation
suggests possibility of building new class of photon tunneling gating devices
for all-optical signal processing.Comment: 11 pages, 3 figure
Nonlocal Optics of Plasmonic Nanowire Metamaterials
We present an analytical description of the nonlocal optical response of
plasmonic nanowire metamaterials that enable negative refraction, subwavelength
light manipulation, and emission lifetime engineering. We show that dispersion
of optical waves propagating in nanowire media results from coupling of
transverse and longitudinal electromagnetic modes supported by the composite
and derive the nonlocal effective medium approximation for this dispersion. We
derive the profiles of electric field across the unit cell, and use these
expressions to solve the long-standing problem of additional boundary
conditions in calculations of transmission and reflection of waves by nonlocal
nanowire media. We verify our analytical results with numerical solutions of
Maxwell's equations and discuss generalization of the developed formalism to
other uniaxial metamaterials
Shaping plasmon beams via the controlled illumination of finite-size plasmonic crystals
Plasmonic crystals provide many passive and active optical functionalities, including enhanced sensing, optical nonlinearities, light extraction from LEDs and coupling to and from subwavelength waveguides. Here we study, both experimentally and numerically, the coherent control of SPP beam excitation in finite size plasmonic crystals under focussed illumination. The correct combination of the illuminating spot size, its position relative to the plasmonic crystal, wavelength and polarisation enables the efficient shaping and directionality of SPP beam launching. We show that under strongly focussed illumination, the illuminated part of the crystal acts as an antenna, launching surface plasmon waves which are subsequently filtered by the surrounding periodic lattice. Changing the illumination conditions provides rich opportunities to engineer the SPP emission pattern. This offers an alternative technique to actively modulate and control plasmonic signals, either via micro- and nano-electromechanical switches or with electro- and all-optical beam steering which have direct implications for the development of new integrated nanophotonic devices, such as plasmonic couplers and switches and on-chip signal demultiplexing. This approach can be generalised to all kinds of surface waves, either for the coupling and discrimination of light in planar dielectric waveguides or the generation and control of non-diffractive SPP beams
Amplification of surface plasmon polaritons in the presence of nonlinearity and spectral signatures of threshold crossover
We describe effects of nonlinearity on propagation of surface plasmon
polaritons (SPPs) at an interface between a metal and an amplifying medium of
the externally pumped two-level atoms. Using Maxwell equations we derive the
nonlinear dispersion law and demonstrate that, the nonlinear saturation of the
linear gain leads to formation of stationary SPP modes with the intensities
independent from the propagation distance. Transition to the regime of
stationary propagation is similar to the threshold crossover in lasers and
leads to narrowing of the SPP spectrum.Comment: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-34-18-286
Magnetic dipole radiation tailored by substrates: numerical investigation
Nanoparticles of high refractive index materials can possess strong magnetic
polarizabilities and give rise to artificial magnetism in the optical spectral
range. While the response of individual dielectric or metal spherical particles
can be described analytically via multipole decomposition in the Mie series,
the influence of substrates, in many cases present in experimental
observations, requires different approaches. Here, the comprehensive numerical
studies of the influence of a substrate on the spectral response of high- index
dielectric nanoparticles were performed. In particular, glass, perfect electric
conductor, gold, and hyperbolic metamaterial substrates were investigated.
Optical properties of nanoparticles were characterized via scattering
cross-section spectra, electric field profiles, and induced electric and
magnetic moments. The presence of substrates was shown to introduce significant
impact on particle's magnetic resonances and resonant scattering
cross-sections. Variation of substrate material provides an additional degree
of freedom in tailoring properties of emission of magnetic multipoles,
important in many applications.Comment: 10 page, 28 figure
Non-minimal Wu-Yang wormhole
We discuss exact solutions of three-parameter non-minimal Einstein-Yang-Mills
model, which describe the wormholes of a new type. These wormholes are
considered to be supported by SU(2)-symmetric Yang-Mills field, non-minimally
coupled to gravity, the Wu-Yang ansatz for the gauge field being used. We
distinguish between regular solutions, describing traversable non-minimal
Wu-Yang wormholes, and black wormholes possessing one or two event horizons.
The relation between the asymptotic mass of the regular traversable Wu-Yang
wormhole and its throat radius is analysed.Comment: 9 pages, 2 figures, typos corrected, 2 references adde
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