4,013 research outputs found
The C9 cluster: Structure and infrared frequencies
The high resolution infrared spectrum of the C9 cluster has been measured in direct absorption by infrared diode laser spectroscopy of a pulsed supersonic carbon cluster jet. Fifty-one rovibrational transitions have been assigned to the nu6 (sigmau ) antisymmetric stretch fundamental of the 1Sigma + 9 linear ground state of C9. The measured rotational constant [429.30(50) MHz] is in good agreement with ab initio calculations and indicates an effective bond length of 1.278 68(75) Å, consistent with cumulenic bonding in this cluster. Several perturbations are observed in the upper state, and the upper- and lower-state centrifugal distortion constants are observed to be anomolously large, evidencing a high degree of Coriolis mixing of the normal modes
Optimal light harvesting structures at optical and infrared frequencies
One-dimensional light harvesting structures with a realistic geometry
nano-patterned on an opaque metallic film are optimized to render high
transmission efficiencies at optical and infrared frequencies. Simple design
rules are developed for the particular case of a slit-groove array with a given
number of grooves that are symmetrically distributed with respect to a central
slit. These rules take advantage of the hybridization of Fabry-Perot modes in
the slit and surface modes of the corrugated metal surface. Same design rules
apply for optical and infrared frequencies. The parameter space of the groove
array is also examined with a conjugate gradient optimization algorithm that
used as a seed the geometries optimized following physical intuition. Both
uniform and nonuniform groove arrays are considered. The largest transmission
enhancement, with respect to a uniform array, is obtained for a chirped groove
profile. Such enhancement is a function of the wavelength. It decreases from
39% in the optical part of the spectrum to 15% at the long wavelength infrared.Comment: 13 pages, 5 figure
Sub-wavelength imaging at infrared frequencies using an array of metallic nanorods
We demonstrate that an array of metallic nanorods enables sub-wavelength
(near-field) imaging at infrared frequencies. Using an homogenization approach,
it is theoretically proved that under certain conditions the incoming radiation
can be transmitted by the array of nanorods over a significant distance with
fairly low attenuation. The propagation mechanism does not involve a resonance
of material parameters and thus the resolution is not strongly affected by
material losses and has wide bandwidth. The sub-wavelength imaging with
resolution by silver rods at 30 THz is demonstrated numerically
using full-wave electromagnetic simulator.Comment: 12 pages, 16 figures, submitted to PR
Topological phase transition in wire medium enables high Purcell factor at infrared frequencies
In this paper, we study topological phase transition in a wire medium
operating at infrared frequencies. This transition occurs in the reciprocal
space between the indefinite (open-surface) regime of the metamaterial to its
dielectric (closed-surface) regime. Due to the spatial dispersion inherent to
wire medium, a hybrid regime turns out to be possible at the transition
frequency. Both such surfaces exist at the same frequency and touch one
another. At this frequency, all values of the axial wavevector correspond to
propagating spatial harmonics. The implication of this regime is the
overwhelming radiation enhancement. We numerically investigated the gain in
radiated power for a sub-wavelength dipole source submerged into such the
medium. In contrast to all previous works, this gain (called the Purcell
factor) turns out to be higher for an axial dipole than for a transversal one
Zone center phonons of the orthorhombic RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
A short range force constant model (SRFCM) has been applied for the first
time to investigate the phonons in RMnO3 (R = Pr, Eu, Tb, Dy, Ho) perovskites
in their orthorhombic phase. The calculations with 17 stretching and bending
force constants provide good agreement for the observed Raman frequencies. The
infrared frequencies have been assigned for the first time.
PACS Codes: 36.20.Ng, 33.20.Fb, 34.20.CfComment: 8 pages, 1 figur
Strong nonlinear optical response of graphene flakes measured by four-wave mixing
We present the first experimental investigation of nonlinear optical
properties of graphene flakes. We find that at near infrared frequencies a
graphene monolayer exhibits a remarkably high third-order optical nonlinearity
which is practically independent of the wavelengths of incident light. The
nonlinear optical response can be utilized for imaging purposes, with image
contrasts of graphene which are orders of magnitude higher than those obtained
using linear microscopy.Comment: 4 pages, 5 figure
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