57 research outputs found

### Ultra-short solitons and kinetic effects in nonlinear metamaterials

We present a stability analysis of a modified nonlinear Schroedinger equation
describing the propagation of ultra-short pulses in negative refractive index
media. Moreover, using methods of quantum statistics, we derive a kinetic
equation for the pulses, making it possible to analyze and describe partial
coherence in metamaterials. It is shown that a novel short pulse soliton, which
is found analytically, can propagate in the medium.Comment: 6 pages, 2 figures, to appear in Phys. Rev.

### Reverse Doppler effect in backward spin waves scattered on acoustic waves

We report on the observation of reverse Doppler effect in backward spin waves
reflected off of surface acoustic waves. The spin waves are excited in a
yttrium iron garnet (YIG) film. Simultaneously, acoustic waves are also
generated. The strain induced by the acoustic waves in the magnetostrictive YIG
film results in the periodic modulation of the magnetic anisotropy in the film.
Thus, in effect, a travelling Bragg grating for the spin waves is produced. The
backward spin waves reflecting off of this grating exhibit a reverse Doppler
shift: shifting down rather than up in frequency when reflecting off of an
approaching acoustic wave. Similarly, the spin waves are shifted up in
frequency when reflecting from receding acoustic waves.Comment: 4 pages, 3 figure

### Electron Beam Instability in Left-Handed Media

We predict that two electron beams can develop an instability when passing
through a slab of left-handed media (LHM). This instability, which is inherent
only for LHM, originates from the backward Cherenkov radiation and results in a
self-modulation of the beams and radiation of electromagnetic waves. These
waves leave the sample via the rear surface of the slab (the beam injection
plane) and form two shifted bright circles centered at the beams. A simulated
spectrum of radiation has well-separated lines on top of a broad continuous
spectrum, which indicates dynamical chaos in the system. The radiation
intensity and its spectrum can be controlled either by the beams' current or by
the distance between the two beams.Comment: 4 pages, 4 figure

### The Dynamics of Charges Induced by a Charged Particle Traversing a Dielectric Slab

We studied the dynamics of surfacea and wake charges induced by a charged
particle traversing a dielectric slab. It is shown that after the crossing of
the slab first boundary, the induced on the slab surface charge (image charge)
is transformed into the wake charge, which overflows to the second boundary
when the particle crosses it. It is also shown, that the polarization of the
slab is of an oscillatory nature, and the net induced charge in a slab remains
zero at all stages of the motion.Comment: 12 pages, 1 figur

### Observation of soft X-ray Cherenkov radiation in Al

The soft X-ray radiation generated by 5.7 MeV electrons from both an Al foil and a Mylar film in forward direction was experimentally studied. A narrow specific directivity, an ultra-narrow spectral bandwidth and a good consistency between the experiment and theory prove that the Cherenkov radiation (CR) with photon energy near the L-edge of absorption in Al was observed. The results demonstrate that the CR spectral-angular properties and the absolute photon yield can be described well enough using Pafomov's theoretical model and Henke's refractive index database, which is essential for all practical applications

### On the possibility of metamaterial properties in spin plasmas

The fluid theory of plasmas is extended to include the properties of electron
spin. The linear theory of waves in a magnetized plasma is presented, and it is
shown that the spin effects causes a change of the magnetic permeability.
Furthemore, by changing the direction of the external magnetic field, the
magnetic permability may become negative. This leads to instabilities in the
long wavelength regimes. If these can be controlled, however, the spin plasma
becomes a metamaterial for a broad range of frequencies, i.e. above the ion
cyclotron frequency but below the electron cyclotron frequency. The
consequences of our results are discussed.Comment: 10 page

### Vector electromagnetic theory of transition and diffraction radiation with application to the measurement of longitudinal bunch size

We have developed a novel method based on vector electromagnetic theory and
Schellkunoff's principles to calculate the spectral and angular distributions
of transtion radiation (TR) and diffraction radiation (DR) produced by a
charged particle interacting with an arbitrary target. The vector method
predicts the polarization and spectral angular distributions of the radiation
at an arbitrary distance form the source, i.e. in both the near and far fields,
and in any direction of observation. The radiation fields of TR and DR
calculated with the commonly used scalar Huygens model are shown to be limiting
forms of those predicted by the vector theory and the regime of validity of the
scalar theory is explicitly shown. Calculations of TR and DR done using the
vector model are compared to results available in the literature for various
limiting cases and for cases of more general interest. Our theory has important
applications in the design of TR and DR diagnostics particularly those that
utilize coherent TR or DR to infer the longitudinal bunch size and shape. A new
technique to determine the bunch length using the angular distribution of
coherent TR or DR is proposed.Comment: 47 pages, 16 figures, accepted for publication in Phys. Rev. ST.
Accel. and Beam

### Bremsstrahlung Suppression due to the LPM and Dielectric Effects in a Variety of Materials

The cross section for bremsstrahlung from highly relativistic particles is
suppressed due to interference caused by multiple scattering in dense media,
and due to photon interactions with the electrons in all materials. We present
here a detailed study of bremsstrahlung production of 200 keV to 500 MeV
photons from 8 and 25 GeV electrons traversing a variety of target materials.
For most targets, we observe the expected suppressions to a good accuracy. We
observe that finite thickness effects are important for thin targets.Comment: 52 pages, 13 figures (incorporated in the revtex LaTeX file

### Control of planar nonlinear guided waves and spatial solitons with a left-handed medium

The evidence that double negative media, with an effective negative
permittivity, and an effective negative permeability, can be manufactured to
operate at frequencies ranging from microwave to optical is ushering in a new
era of metamaterials. They are referred to here as 'left-handed', even though a
variety of names is evident from the literature. In anticipation of a demand
for highly structured integrated practical waveguides, this paper addresses the
impact of this type of medium upon waveguides that can be also nonlinear. After
an interesting historical overview and an exposure of some straightforward
concepts, a planar guide is investigated, in which the waveguide is a slab
consisting of a left-handed medium sandwiched between a substrate and cladding
that are simple dielectrics. The substrate and cladding display a Kerr-type
nonlinear response. Because of the nonlinear properties of the Kerr media, the
power flow direction can be controlled by the intensity of the electric field.
A comprehensive finite-difference-time-domain (FDTD) analysis is presented that
concentrates upon spatial soliton behaviour. An interesting soliton-lens
arrangement is investigated that lends itself to a novel cancellation effect.Comment: 19 pages, 11 figure

- â€¦