560 research outputs found
Periodic transmission peak splitting in one dimensional disordered photonic structures
In the present paper we present ways to modulate the periodic transmission
peaks arising in disordered one dimensional photonic structures with hundreds
of layers. Disordered structures in which the optical length nd (n is the
refractive index and d the layer thickness) is the same for each layer show
regular peaks in their transmission spectra. A proper variation of the optical
length of the layers leads to a splitting of the transmission peaks. Notably,
the variation of the occurrence of high and low refractive index layers, gives
a tool to tune also the width of the peaks. These results are of highest
interest for optical application, such as light filtering, where the manifold
of parameters allows a precise design of the spectral transmission ranges.Comment: 5 pages, 3 figure
Photo-thermal effect with photonic crystals for photocatalysis and water desalination
The demand of water is absolutely important for irrigation, industrial processes and domestic use. An interesting strategy to cope with the increasing water need is water desalination, which can be pursued with several strategies. Usually, the energy requirement of desalination plants is rather high. Membrane distillation is a good alternative, but it requires a non negligible amount of energy to heat the input water. Photothermal effects that exploit photonic structures can overcome this problem. In this review, we report significant works that employ photonic devices for water desalination. Moreover, we envisage the use of low-cost and easy-to-design one-dimensional photonic crystals and random photonic structures as photothermal devices
Black Phosphorus based One-dimensional Photonic Crystals and Microcavities
The latest achievements in the fabrication of black phosphorus thin layers,
towards the technological breakthrough of a phosphorene atomically thin layer,
are paving the way for a their employment in electronics, optics, and
optoelectronics. In this work, we have simulated the optical properties of
one-dimensional photonic structures, i.e. photonic crystals and microcavities,
in which few-layer black phosphorus is one of the components. The insertion of
the 5 nm black phosphorous layers leads to a photonic band gap in the photonic
crystals and a cavity mode in the microcavity interesting for light
manipulation and emission enhancement.Comment: 7 pages, 4 figure
Colloidal CuFeS2 Nanocrystals: Intermediate Fe d-Band Leads to High Photothermal Conversion Efficiency
We describe the colloidal hot-injection synthesis of phase-pure nanocrystals
(NCs) of a highly abundant mineral, chalcopyrite (CuFeS2). Absorption bands
centered at around 480 and 950 nm, spanning almost the entire visible and near
infrared regions, encompass their optical extinction characteristics. These
peaks are ascribable to electronic transitions from the valence band (VB) to
the empty intermediate band (IB), located in the fundamental gap and mainly
composed of Fe 3d orbitals. Laser-irradiation (at 808 nm) of an aqueous
suspension of CuFeS2 NCs exhibited significant heating, with a photothermal
conversion efficiency of 49%. Such efficient heating is ascribable to the
carrier relaxation within the broad IB band (owing to the indirect VB-IB gap),
as corroborated by transient absorption measurements. The intense absorption
and high photothermal transduction efficiency (PTE) of these NCs in the
so-called biological window (650-900 nm) makes them suitable for photothermal
therapy as demonstrated by tumor cell annihilation upon laser irradiation. The
otherwise harmless nature of these NCs in dark conditions was confirmed by in
vitro toxicity tests on two different cell lines. The presence of the deep Fe
levels constituting the IB is the origin of such enhanced PTE, which can be
used to design other high performing NC photothermal agents.Comment: 12 pages, Chemistry of Materials, 31-May-201
Stretching and Heating Single DNA Molecules with Optically Trapped Gold-Silica Janus Particles
Self-propelled micro- and nanoscale motors are capable of autonomous motion typically by inducing local concentration gradients or thermal gradients in their surrounding medium. This is a result of the heterogeneous surface of the self-propelled structures that consist of materials with different chemical or physical properties. Here we present a self-thermophoretically driven Auâsilica Janus particle that can simultaneously stretch and partially melt a single double-stranded DNA molecule. We show that the effective force acting on the DNA molecule is in the âŒpN range, well suited to probe the entropic stretching regime of DNA, and we demonstrate that the local temperature enhancement around the gold side of the particle produces partial DNA dehybridization
Query processing of spatial objects: Complexity versus Redundancy
The management of complex spatial objects in applications, such as geography and cartography,
imposes stringent new requirements on spatial database systems, in particular on efficient
query processing. As shown before, the performance of spatial query processing can be improved
by decomposing complex spatial objects into simple components. Up to now, only decomposition
techniques generating a linear number of very simple components, e.g. triangles or trapezoids, have
been considered. In this paper, we will investigate the natural trade-off between the complexity of
the components and the redundancy, i.e. the number of components, with respect to its effect on
efficient query processing. In particular, we present two new decomposition methods generating
a better balance between the complexity and the number of components than previously known
techniques. We compare these new decomposition methods to the traditional undecomposed representation
as well as to the well-known decomposition into convex polygons with respect to their
performance in spatial query processing. This comparison points out that for a wide range of query
selectivity the new decomposition techniques clearly outperform both the undecomposed representation
and the convex decomposition method. More important than the absolute gain in performance
by a factor of up to an order of magnitude is the robust performance of our new decomposition
techniques over the whole range of query selectivity
Large scale indium tin oxide (ITO) one dimensional gratings for ultrafast signal modulation in the visible spectral region
Indium tin oxide (ITO) is a heavily doped semiconductor with a plasmonic response in the near infrared region. When exposed to light, the distribution of conduction band electron induces a change in the real and imaginary parts of the dielectric permittivity. The coupling of the electromagnetic waves with the electrons in the conduction band of metallic nanostructures with ultrashort light pulses results in a nonlinear plasmonic response. Such optical modulation occurring on ultrafast time scales, e.g. picosecond response times, can be exploited and used to create integrated optical components with terahertz modulation speed. Here, we present a photophysical study on a one dimensional ITO grating, realized using a femtosecond micromachining process, a very industrially accessible technology. The geometries, dimensions and pitch of the various gratings analyzed are obtained by means of direct ablation in a controlled atmosphere of a homogeneous thin layer of ITO deposited on a glass substrate. The pitch has been selected in order to obtain a higher order of the photonic band gap in the visible spectral region. Femtosecond micromachining technology guarantees precision, repeatability and extreme manufacturing flexibility. By means of ultrafast pump-probe spectroscopy, we characterize both the plasmon and inter-band temporal dynamics. We observe a large optical nonlinearity of the ITO grating in the visible range, where the photonic band gap occurs, when pumped at the surface plasmon resonance in the near infrared (1500 nm) region. All together, we show the possibility of all-optical signal modulation with heavily doped semiconductors in their transparency window with a picosecond response time through the formation of ITO grating structures
The Epistemology of Intentionality: Notional Constituents vs. Direct Grasp
Franz Brentano is well known for highlighting the importance of intentionality, but he said curiously little about the nature of intentionality. According to Mark Textor, there is a deep reason for this: Brentano took intentionality to be a conceptual primitive the nature of which is revealed only in direct grasp. Although there is certainly textual support for this interpretation, it appears in tension with Brentanoâs repeated attempts to analyze intentionality in terms of ânotional constituentsâ â aspects of intentionality which cannot come apart in reality but which can be conceptually distinguished. After bringing out this tension, I explore some options for resolving it, ultimately offering my own favored interpretation
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