846 research outputs found
Rigorous analysis of grazing-angle scattering of electromagnetic waves in periodic gratings
Grazing-angle scattering (GAS) is a type of Bragg scattering of waves in
slanted non-uniform periodic gratings, when the diffracted order satisfying the
Bragg condition propagates at a grazing angle with respect to the boundaries of
a slab-like grating. Rigorous analysis of GAS of bulk TE electromagnetic waves
is undertaken in holographic gratings by means of the enhanced T-matrix
algorithm. A comparison of the rigorous and the previously developed
approximate theories of GAS is carried out. A complex pattern of numerous
previously unknown resonances is discovered and analysed in detail for gratings
with large amplitude, for which the approximate theory fails. These resonances
are associated not only with the geometry of GAS, but are also typical for wide
transmitting gratings. Their dependence on grating amplitude, angles of
incidence and scattering, and grating width is investigated numerically.
Physical interpretation of the predicted resonances is linked to the existence
and the resonant generation of special new eigenmodes of slanted gratings. Main
properties of these modes and their field structure are discussed.Comment: 21 pages, 13 figure
Non-steady-state extremely asymmetrical scattering of waves in periodic gratings
Extremely asymmetrical scattering (EAS) is a highly resonant type of Bragg
scattering with a strong resonant increase of the scattered wave amplitude
inside and outside the grating. EAS is realized when the scattered wave
propagates parallel to the grating boundaries. We present a rigorous algorithm
for the analysis of non-steady-state EAS, and investigate the relaxation of the
incident and scattered wave amplitudes to their steady-state values.
Non-steady-state EAS of bulk TE electromagnetic waves is analyzed in narrow and
wide, slanted, holographic gratings. Typical relaxation times are determined
and compared with previous rough estimations. Physical explanation of the
predicted effects is presented.Comment: 7 pages, 3 figures. This paper is freely available online at
http://www.opticsexpress.org/abstract.cfm?URI=OPEX-10-6-268 which includes
multimedia files not included in this preprint versio
Rigorous analysis of extremely asymmetrical scattering of electromagnetic waves in slanted periodic gratings
Extremely asymmetrical scattering (EAS) is a new type of Bragg scattering in
thick, slanted, periodic gratings. It is realised when the scattered wave
propagates parallel to the front boundary of the grating. Its most important
feature is the strong resonant increase in the scattered wave amplitude
compared to the amplitude of the incident wave: the smaller the grating
amplitude, the larger the amplitude of the scattered wave. In this paper,
rigorous numerical analysis of EAS is carried out by means of the enhanced
T-matrix algorithm. This includes investigation of harmonic generation inside
and outside the grating, unusually strong edge effects, fast oscillations of
the incident wave amplitude in the grating, etc. Comparison with the previously
developed approximate theory is carried out. In particular, it is demonstrated
that the applicability conditions for the two-wave approximation in the case of
EAS are noticeably more restrictive than those for the conventional Bragg
scattering. At the same time, it is shown that the approximate theory is
usually highly accurate in terms of description of EAS in the most interesting
cases of scattering with strong resonant increase of the scattered wave
amplitude. Physical explanation of the predicted effects is presented.Comment: 14 pages, 7 figures; v2: corrections to metadata and bibliographical
info in preprin
Nanoscale Fabry-Perot Interferometer Using Channel Plasmon-Polaritons in Triangular Metallic Grooves
In this letter, we demonstrate the possibility of an effective nano-scale Fabry-Perot interferometer in a sub-wavelength plasmonic waveguide in the form of a triangular groove on a metal surface, guiding channel plasmon-polaritons (CPPs). The resonant cavity is formed by two semitransparent metal membranes (mirrors) placed into the groove. Effective filtering effect of the cavity is demonstrated, resulting in single-mode output from the cavity. Typical quality factor for the cavity of the resonant length is determined to be Q ~ 100 for the silver-vacuum structure with the 30 degree groove angle. Possible ways of increasing this factor are discussed
Extremely asymmetrical scattering in gratings with varying mean structural parameters
Extremely asymmetrical scattering (EAS) is an unusual type of Bragg
scattering in slanted periodic gratings with the scattered wave (the +1
diffracted order) propagating parallel to the grating boundaries. Here, a
unique and strong sensitivity of EAS to small stepwise variations of mean
structural parameters at the grating boundaries is predicted theoretically (by
means of approximate and rigorous analyses) for bulk TE electromagnetic waves
and slab optical modes of arbitrary polarization in holographic (for bulk
waves) and corrugation (for slab modes) gratings. The predicted effects are
explained using one of the main physical reasons for EAS--the diffractional
divergence of the scattered wave (similar to divergence of a laser beam). The
approximate method of analysis is based on this understanding of the role of
the divergence of the scattered wave, while the rigorous analysis uses the
enhanced T-matrix algorithm. The effect of small and large stepwise variations
of the mean permittivity at the grating boundaries is analysed. Two distinctly
different and unusual patterns of EAS are predicted in the cases of wide and
narrow (compared to a critical width) gratings. Comparison between the
approximate and rigorous theories is carried out.Comment: 16 pages, 5 figure
Extremely asymmetrical scattering of electromagnetic waves in gradually varying periodic arrays
This paper analyses theoretically and numerically the effect of varying
grating amplitude on the extremely asymmetrical scattering (EAS) of bulk and
guided optical modes in non-uniform strip-like periodic Bragg arrays with
stepwise and gradual variations in the grating amplitude across the array. A
recently developed new approach based on allowance for the diffractional
divergence of the scattered wave is used for this analysis. It is demonstrated
that gradual variations in magnitude of the grating amplitude may change the
pattern of EAS noticeably but not radically. On the other hand, phase
variations in the grating may result in a radically new type of Bragg
scattering - double-resonant EAS (DEAS). In this case, a combination of two
strong simultaneous resonances (one with respect to frequency, and another with
respect to the phase variation) is predicted to take place in non-uniform
arrays with a step-like phase and gradual magnitude variations of the grating
amplitude. The tolerances of EAS and DEAS to small gradual variations in the
grating amplitude are determined. The main features of these types of
scattering in non-uniform arrays are explained by the diffractional divergence
of the scattered wave inside and outside the array.Comment: 13 pages, 10 figure
Double-resonant extremely asymmetrical scattering of electromagnetic waves in periodic arrays separated by a gap
Two strong simultaneous resonances of scattering--double-resonant extremely
asymmetrical scattering (DEAS)--are predicted in two parallel, oblique,
periodic Bragg arrays separated by a gap, when the scattered wave propagates
parallel to the arrays. One of these resonances is with respect to frequency
(which is common to all types of Bragg scattering), and another is with respect
to phase variation between the arrays. The diffractional divergence of the
scattered wave is shown to be the main physical reason for DEAS in the
considered structure. Although the arrays are separated, they are shown to
interact by means of the diffractional divergence of the scattered wave across
the gap from one array into the other. It is also shown that increasing
separation between the two arrays results in a broader and weaker resonance
with respect to phase shift. The analysis is based on a recently developed new
approach allowing for the diffractional divergence of the scattered wave inside
and outside the arrays. Physical interpretations of the predicted features of
DEAS in separated arrays are also presented. Applicability conditions for the
developed theory are derived.Comment: 8 pages, 5 figure
Anomalous absorption of bulk shear sagittal acoustic waves in a layered structure with viscous fluid
It is demonstrated theoretically that the absorptivity of bulk shear sagittal
waves by an ultra-thin layer of viscous fluid between two different elastic
media has a strong maximum (in some cases as good as 100%) at an optimal layer
thickness. This thickness is usually much smaller than the penetration depths
and lengths of transverse and longitudinal waves in the fluid. The angular
dependencies of the absorptivity are demonstrated to have significant and
unusual structure near critical angles of incidence. The effect of
non-Newtonian properties and non-uniformities of the fluid layer on the
absorptivity is also investigated. In particular, it is shown that the
absorption in a thin layer of viscous fluid is much more sensitive to non-zero
relaxation time(s) in the fluid layer than the absorption at an isolated
solid-fluid interface.Comment: 14 pages, 8 figure
Femme au chapeau: Art, Fashion and the Woman's Hat in Belle Epoque Paris
This thesis examines the images of hatted women in the early 1900s among Paris-based artists, when the fast pace of the fashion industry and changing media revolutionised the image of a fashionable woman. The first chapter examines the hat in portraiture of the early twentieth century, in both academic and avant-garde art, with emphasis on the depiction of glamour, and how a woman’s identity might be altered by a hat. It draws a comparison between commercial portraiture, and portraits of women by avant-garde artists. The second chapter addresses the images of the popular Montmartre dance hall, the Moulin de la Galette, both in paintings and in print media. The focus is on the “fantasy,” whereby a temporary and alternative identity is created for a woman through her headgear. The final chapter examines the evolution of the hat to its largest and most elaborate state at Parisian horse-racing events, addressing the obsession with size, and the environmental impact of the millinery trade in its pursuit of ever-increasing grandeur
Grazing-angle scattering of electromagnetic waves in gratings with varying mean parameters: grating eigenmodes
A highly unusual pattern of strong multiple resonances for bulk
electromagnetic waves is predicted and analysed numerically in thick periodic
holographic gratings in a slab with the mean permittivity that is larger than
that of the surrounding media. This pattern is shown to exist in the geometry
of grazing-angle scattering (GAS), that is when the scattered wave (+1
diffracted order) in the slab propagates almost parallel to the slab (grating)
boundaries. The predicted resonances are demonstrated to be unrelated to
resonant generation of the conventional guided modes of the slab. Their
physical explanation is associated with resonant generation of a completely new
type of eigenmodes in a thick slab with a periodic grating. These new slab
eigenmodes are generically related to the grating; they do not exist if the
grating amplitude is zero. The field structure of these eigenmodes and their
dependence on structural and wave parameters is analysed. The results are
extended to the case of GAS of guided modes in a slab with a periodic groove
array of small corrugation amplitude and small variations in the mean thickness
of the slab at the array boundaries.Comment: 16 pages, 6 figure
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