725 research outputs found
Polymer nanofibers as novel light-emitting sources and lasing material
Polymer micro- and nano-fibers, made of organic light-emitting materials with
optical gain, show interesting lasing properties. Fibers with diameters from
few tens of nm to few microns can be fabricated by electrospinning, a method
based on electrostatic fields applied to a polymer solution. The morphology and
emission properties of these fibers, composed of optically inert polymers
embedding laser dyes, are characterized by scanning electron and fluorescence
microscopy, and lasing is observed under optical pumping for fluences of the
order of 10^2 microJ cm^-2. In addition, light-emitting fibers can be
electrospun by conjugated polymers, their blends, and other active organics,
and can be exploited in a range of photonic and electronic devices. In
particular, waveguiding of light is observed and characterized, showing optical
loss coefficient in the range of 10^2-10^3 cm^-1. The reduced size of these
novel laser systems, combined with the possibility of achieving wavelength
tunability through transistor or other electrode-based architectures embedding
non-linear molecular layers, and with their peculiar mechanical robustness,
open interesting perspectives for realizing miniaturized laser sources to
integrate on-chip optical sensors and photonic circuits.Comment: 7 pages, 3 figures, 27 references. Invited contribution. Copyright
(2013) Society of Photo Optical Instrumentation Engineers. One print or
electronic copy may be made for personal use only. Systematic reproduction
and distribution, duplication of any material in this paper for a fee or for
commercial purposes, or modification of the content of the paper are
prohibite
Scoperta di pattern ripetuti mediante l'uso di alberi PQ
In questo lavoro è stata affrontata e studiata una nuova tecnica interessante ed utile per l’estrazione e la scoperta di pattern da sequenze biologiche. Per far ciò, è stata utilizzata la struttura dati degli "Alberi PQ"
Emission properties of electrospun polymeric nanofibres
The emission properties of polymer nanofibres fabricated by electrospinning are analysed. The nanofibres, made by conjugated polymers, display diameters of few hundreds of nanometers, depending on the process parameters, and exhibit photoluminescence tunable in the visible spectral range and polarized along the fibre axis. Nonradiative energy transfer in fibres made by blends of polymers and its exploitation for emission tuning are discussed
A nanophotonic laser on a graph
Conventional nano-photonic schemes minimise multiple scattering to realise a
miniaturised version of beam-splitters, interferometers and optical cavities
for light propagation and lasing. Here instead, we introduce a nanophotonic
network built from multiple paths and interference, to control and enhance
light-matter interaction via light localisation. The network is built from a
mesh of subwavelength waveguides, and can sustain localised modes and
mirror-less light trapping stemming from interference over hundreds of nodes.
With optical gain, these modes can easily lase, reaching 100 pm
linewidths. We introduce a graph solution to the Maxwell's equation which
describes light on the network, and predicts lasing action. In this framework,
the network optical modes can be designed via the network connectivity and
topology, and lasing can be tailored and enhanced by the network shape.
Nanophotonic networks pave the way for new laser device architectures, which
can be used for sensitive biosensing and on-chip optical information
processing
Modal Coupling of Single Photon Emitters Within Nanofiber Waveguides
Nanoscale generation of individual photons in confined geometries is an
exciting research field aiming at exploiting localized electromagnetic fields
for light manipulation. One of the outstanding challenges of photonic systems
combining emitters with nanostructured media is the selective channelling of
photons emitted by embedded sources into specific optical modes and their
transport at distant locations in integrated systems. Here, we show that
soft-matter nanofibers, electrospun with embedded emitters, combine
subwavelength field localization and large broadband near-field coupling with
low propagation losses. By momentum spectroscopy, we quantify the modal
coupling efficiency identifying the regime of single-mode coupling. These
nanofibers do not rely on resonant interactions, making them ideal for
room-temperature operation, and offer a scalable platform for future quantum
information technology
3D printing of optical materials: an investigation of the microscopic properties
3D printing technologies are currently enabling the fabrication of objects
with complex architectures and tailored properties. In such framework, the
production of 3D optical structures, which are typically based on optical
transparent matrices, optionally doped with active molecular compounds and
nanoparticles, is still limited by the poor uniformity of the printed
structures. Both bulk inhomogeneities and surface roughness of the printed
structures can negatively affect the propagation of light in 3D printed optical
components. Here we investigate photopolymerization-based printing processes by
laser confocal microscopy. The experimental method we developed allows the
printing process to be investigated in-situ, with microscale spatial
resolution, and in real-time. The modelling of the photo-polymerization
kinetics allows the different polymerization regimes to be investigated and the
influence of process variables to be rationalized. In addition, the origin of
the factors limiting light propagation in printed materials are rationalized,
with the aim of envisaging effective experimental strategies to improve optical
properties of printed materials.Comment: 8 pages, 3 figure
Near-field electrospinning of conjugated polymer light-emitting nanofibers
The authors report on the realization of ordered arrays of light-emitting
conjugated polymer nanofibers by near-field electrospinning. The fibers, made
by poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], have diameters of
few hundreds of nanometers and emission peaked at 560 nm. The observed
blue-shift compared to the emission from reference films is attributed to
different polymer packing in the nanostructures. Optical confinement in the
fibers is also analyzed through self-waveguided emission. These results open
interesting perspectives for realizing complex and ordered architectures by
light-emitting nanofibers, such as photonic circuits, and for the precise
positioning and integration of conjugated polymer fibers into light-emitting
devices.Comment: 11 pages, 6 figures Nanoscale, 201
The conformational evolution of elongated polymer solutions tailors the polarization of light-emission from organic nanofibers
Polymer fibers are currently exploited in tremendously important
technologies. Their innovative properties are mainly determined by the behavior
of the polymer macromolecules under the elongation induced by external
mechanical or electrostatic forces, characterizing the fiber drawing process.
Although enhanced physical properties were observed in polymer fibers produced
under strong stretching conditions, studies of the process-induced nanoscale
organization of the polymer molecules are not available, and most of fiber
properties are still obtained on an empirical basis. Here we reveal the
orientational properties of semiflexible polymers in electrospun nanofibers,
which allow the polarization properties of active fibers to be finely
controlled. Modeling and simulations of the conformational evolution of the
polymer chains during electrostatic elongation of semidilute solutions
demonstrate that the molecules stretch almost fully within less than 1 mm from
jet start, increasing polymer axial orientation at the jet center. The
nanoscale mapping of the local dichroism of individual fibers by polarized
near-field optical microscopy unveils for the first time the presence of an
internal spatial variation of the molecular order, namely the presence of a
core with axially aligned molecules and a sheath with almost radially oriented
molecules. These results allow important and specific fiber properties to be
manipulated and tailored, as here demonstrated for the polarization of emitted
light.Comment: 45 pages, 10 figures, Macromolecules (2014
Surface-enhanced Raman spectroscopy in 3D electrospun nanofiber mats coated with gold nanorods
Nanofibers functionalized by metal nanostructures and particles are exploited
as effective flexible substrates for SERS analysis. Their complex
three-dimensional structure may provide Raman signals enhanced by orders of
magnitude compared to untextured surfaces. Understanding the origin of such
improved performances is therefore very important for pushing nanofiber-based
analytical technologies to their upper limit. Here we report on polymer
nanofiber mats which can be exploited as substrates for enhancing the Raman
spectra of adsorbed probe molecules. The increased surface area and the
scattering of light in the nanofibrous system are individually analyzed as
mechanisms to enhance Raman scattering. The deposition of gold nanorods on the
fibers further amplifies Raman signals due to SERS. This study suggests that
Raman signals can be finely tuned in intensity and effectively enhanced in
nanofiber mats and arrays by properly tailoring the architecture, composition,
and light-scattering properties of the complex networks of filaments.Comment: 29 pages, 9 figures, 1 Tabl
- …