544 research outputs found
Electromagnetic wave propagation through a dielectric-chiral interface and through a chiral slab
The reflection from and transmission through a semi-infinite chiral medium are analyzed by obtaining the Fresnel equations in terms of parallel- and perpendicular-polarized modes, and a comparison is made with results reported previously. The chiral medium is described electromagnetically by the constitutive relations D = ΔE + iÎłB and H = iÎłE + (1/ÎŒ)B. The constants Δ, ÎŒ, and Îł are real and have values that are fixed by the size, the shape, and the spatial distribution of the elements that collectively compose the medium. The conditions are obtained for the total internal reflection of the incident wave from the interface and for the existence of the Brewster angle. The effects of the chirality on the polarization and the intensity of the reflected wave from the chiral half-space are discussed and illustrated by using the Stokes parameters. The propagation of electromagnetic waves through an infinite slab of chiral medium is formulated for oblique incidence and solved analytically for the case of normal incidence
FDTD analysis of the tunneling and growing exponential in a pair of epsilon-negative and mu-negative slabs
Pairing together material slabs with opposite signs for the real parts of
their constitutive parameters has been shown to lead to interesting and
unconventional properties that are not otherwise observable for single slabs.
One such case was demonstrated analytically for the conjugate (i.e.,
complementary) pairing of infinite planar slabs of epsilon-negative (ENG) and
mu-negative (MNG) media [A. Alu, and N. Engheta, IEEE Trans. Antennas Prop.,
51, 2558 (2003)]. There it was shown that when these two slabs are juxtaposed
and excited by an incident plane wave, resonance, complete tunneling, total
transparency and reconstruction of evanescent waves may occur in the
steady-state regime under a monochromatic excitation, even though each of the
two slabs by itself is essentially opaque to the incoming radiation. This may
lead to virtual imagers with sub-wavelength resolution and other anomalous
phenomena overcoming the physical limit of diffraction. Here we explore how a
transient sinusoidal signal that starts at t = 0 interacts with such an ENG-MNG
pair of finite size using an FDTD technique. Multiple reflections and
transmissions at each interface are shown to build up to the eventual steady
state response of the pair, and during this process one can observe how the
growing exponential phenomenon may actually occur inside this bilayer.Comment: 14 pages, 9 figures, submitted to Phys Rev
Circuit elements at optical frequencies: nano-inductors, nano-capacitors and nano-resistors
We present some ideas for synthesizing nanocircuit elements in the optical
domain using plasmonic and non-plasmonic nanoparticles. Three basic circuit
elements, i.e., nano-inductors, nano-capacitors, and nano-resistors, are
discussed in terms of small nanostructures with different material properties.
Coupled nanocircuits and parallel and series combinations are also envisioned,
which may provide road maps for the synthesis of more complex nanocircuits in
the IR and visible bands. Ideas for the optical implementation of right-handed
and left-handed nano-transmission lines are also forecasted.Comment: 14 pages, 5 figures, submitted to Physical Review Letter
Manipulation of Giant Faraday Rotation in Graphene Metasurfaces
Faraday rotation is a fundamental magneto-optical phenomenon used in various
optical control and magnetic field sensing techniques. Recently, it was shown
that a giant Faraday rotation can be achieved in the low-THz regime by a single
monoatomic graphene layer. Here, we demonstrate that this exceptional property
can be manipulated through adequate nano-patterning, notably achieving giant
rotation up to 6THz with features no smaller than 100nm. The effect of the
periodic patterning on the Faraday rotation is predicted by a simple physical
model, which is then verified and refined through accurate full-wave
simulations.Comment: 4 pages, 5 figures, submitted to Applied Physics Letter
Coupling between a dark and a bright eigenmode in a terahertz metamaterial
Terahertz time domain spectroscopy and rigorous simulations are used to probe
the coupling between a dark and a bright plasmonic eigenmode in a metamaterial
with broken symmetry. The metamaterial consists of two closely spaced split
ring resonators that have their gaps in non-identical positions within the
ring. For normal incidence and a fixed polarization both lowest order
eigenmodes of the split ring resonators can be excited; although one of them
has to be regarded as dark since coupling is prohibited because of symmetry
constraints. Emphasis in this work is put on a systematic evaluation of the
coupling effects depending on a spectral tuning of both resonances
Trapped mode resonances in metalo-dielectric structures with electric asymmetry materials
This paper investigates the possibility of exciting high quality trapped resonant modes on frequency selective surfaces consisting of identical sub-wavelength metallic inclusions (symmetrically split rings) with no structural asymmetry but exhibitting electrical asymmetry. The electrical symmetry is broken by using different dielectric substrates. The existence of such anti-symmetric trapped mode on geometrical symmetric structure is demonstrated through numerical simulation. Numerical results suggest that the high quality factor observed for these resonant modes is achieved via weak coupling between the "trapped modes" and free space which enables the excitation of these modes
Theoretical study of variation of propagation constant in a cylindrical waveguide due to chirality: chiro-phase shifting
Miniaturization of photonic waveguides by the use of left-handed materials
We propose the use of a left-handed material in an optical waveguide
structure to reduce its thickness well below the wavelength of light. We
demonstrate that a layer of left-handed material, added to the cladding of a
planar waveguide rather than to its core, allows for good light confinement in
a subwavelength thin waveguide. We attribute the observed behavior to the
change in phase evolution of electromagnetic waves in the guide. This technique
can be used for the miniaturization of photonic integrated circuits.Comment: 4 pages, 4 figure
An Effective Medium Approach to Electron Waves: Graphene Superlattices
We develop an effective medium approach to characterize the propagation of
matter waves in periodic structures, such as graphene or semiconductor
superlattices. It is proven that the time evolution of the states that are not
more localized in space than the characteristic period of the structure can be
described exactly through an effective Hamiltonian, and that the electronic
band structure of the system can be exactly determined from the effective
Hamiltonian. As an illustration of the application of the method, we
characterize the mesoscopic response of graphene superlattices. It is shown
that these structures may be described using simply two effective parameters: a
dispersive potential, and an anisotropy tensor that characterizes the
pseudospin. Our model predicts that a graphene superlattice characterized by an
indefinite anisotropy tensor - such that the eigenvalues of the tensor have
opposite signs - may permit the perfect tunneling of all the stationary states
with a specific value of the energy when it is paired with a dual graphene
superlattice with positive definite anisotropy tensor.Comment: 36 page
Kinetics of Recovery of the Dark-adapted Salamander Rod Photoresponse
The kinetics of the dark-adapted salamander rod photocurrent response to flashes producing from 10 to 105 photoisomerizations (Ί) were investigated in normal Ringer's solution, and in a choline solution that clamps calcium near its resting level. For saturating intensities ranging from âŒ102 to 104 Ί, the recovery phases of the responses in choline were nearly invariant in form. Responses in Ringer's were similarly invariant for saturating intensities from âŒ103 to 104 Ί. In both solutions, recoveries to flashes in these intensity ranges translated on the time axis a constant amount (Ïc) per e-fold increment in flash intensity, and exhibited exponentially decaying âtail phasesâ with time constant Ïc. The difference in recovery half-times for responses in choline and Ringer's to the same saturating flash was 5â7 s. Above âŒ104 Ί, recoveries in both solutions were systematically slower, and translation invariance broke down. Theoretical analysis of the translation-invariant responses established that Ïc must represent the time constant of inactivation of the disc-associated cascade intermediate (R*, G*, or PDE*) having the longest lifetime, and that the cGMP hydrolysis and cGMP-channel activation reactions are such as to conserve this time constant. Theoretical analysis also demonstrated that the 5â7-s shift in recovery half-times between responses in Ringer's and in choline is largely (4â6 s) accounted for by the calcium-dependent activation of guanylyl cyclase, with the residual (1â2 s) likely caused by an effect of calcium on an intermediate with a nondominant time constant. Analytical expressions for the dim-flash response in calcium clamp and Ringer's are derived, and it is shown that the difference in the responses under the two conditions can be accounted for quantitatively by cyclase activation. Application of these expressions yields an estimate of the calcium buffering capacity of the rod at rest of âŒ20, much lower than previous estimates
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