2,184 research outputs found
Light propagation and emission in complex photonic media
We provide an introduction to complex photonic media, that is, composite
materials with spatial inhomogeneities that are distributed over length scales
comparable to or smaller than the wavelength of light. This blossoming field is
firmly rooted in condensed matter physics, in optics, and in materials science.
Many stimulating analogies exist with other wave phenomena such as sound and
seismology, X-rays, neutrons. The field has a rich history, which has led to
many applications in lighting, novel lasers, light harvesting, microscopy, and
bio optics. We provide a brief overview of complex photonic media with
different classes of spatial order, varying from completely random to
long-periodically ordered structures, quasi crystalline and aperiodic
structures, and arrays of cavities. In addition to shaping optical waves by
suitable photonic nanostructures, the realization is quickly arising that the
spatial shaping of optical wavefronts with spatial light modulators
dramatically increases the number of control parameters. As a result, it is
becoming possible for instance to literally see through completely opaque
complex media. We discuss a unified view of complex photonic media by means of
a photonic interaction strength parameter. This parameter gauges the
interaction of light with any complex photonic medium, and allows to compare
complex media from different classes for similar applications.Comment: 8 pages, 2 figures, Light Localisation and Lasing: Random and
Quasi-Random Photonic Structures, Eds. M. Ghulinyan and L. Pavesi, (Cambridge
Univ. Press, Cambridge, 2015) Ch. 1, p.
Local density of optical states in the band gap of a finite photonic crystal
We study the local density of states (LDOS) in a finite photonic crystal, in
particular in the frequency range of the band gap. We propose a new point of
view on the band gap, which we consider to be the result of vacuum fluctuations
in free space that tunnel in the forbidden range in the crystal. As a result,
we arrive at a model for the LDOS that is in two major items modified compared
to the well-known expression for infinite crystals. Firstly, we modify the
Dirac delta functions to become Lorentzians with a width set by the crystal
size. Secondly, building on characterization of the fields versus frequency and
position we calculated the fields in the band gap. We start from the fields at
the band edges, interpolated in space and position, and incorporating the
exponential damping in the band gap. We compare our proposed model to exact
calculations in one dimension using the transfer matrix method and find very
good agreement. Notably, we find that in finite crystals, the LDOS depends on
frequency, on position, and on crystal size, in stark contrast to the
well-known results for infinite crystals.Comment: 22 pages, 8 figure
Selective coupling of optical energy into the fundamental diffusion mode of a scattering medium
We demonstrate experimentally that optical wavefront shaping selectively
couples light into the fundamental diffusion mode of a scattering medium. The
total energy density inside a scattering medium of zinc oxide (ZnO)
nanoparticles was probed by measuring the emitted fluorescent power of spheres
that were randomly positioned inside the medium. The fluorescent power of an
optimized incident wave front is observed to be enhanced compared to a
non-optimized incident front. The observed enhancement increases with sample
thickness. Based on diffusion theory, we derive a model wherein the
distribution of energy density of wavefront-shaped light is described by the
fundamental diffusion mode. The agreement between our model and the data is
striking not in the least since there are no adjustable parameters. Enhanced
total energy density is crucial to increase the efficiency of white LEDs, solar
cells, and of random lasers, as well as to realize controlled illumination in
biomedical optics.Comment: 5 pages, 5 figure
3D spatially-resolved optical energy density enhanced by wavefront shaping
We study the three-dimensional (3D) spatially-resolved distribution of the
energy density of light in a 3D scattering medium upon the excitation of open
transmission channels. The open transmission channels are excited by spatially
shaping the incident optical wavefronts. To probe the local energy density, we
excite isolated fluorescent nanospheres distributed inside the medium. From the
spatial fluorescent intensity pattern we obtain the position of each
nanosphere, while the total fluorescent intensity gauges the energy density.
Our 3D spatially-resolved measurements reveal that the local energy density
versus depth (z) is enhanced up to 26X at the back surface of the medium, while
it strongly depends on the transverse (x; y) position. We successfully
interpret our results with a newly developed 3D model that considers the
time-reversed diffusion starting from a point source at the back surface. Our
results are relevant for white LEDs, random lasers, solar cells, and biomedical
optics
Observation of Intensity Statistics of Light Transmitted Through 3D Random Media
We experimentally observe the spatial intensity statistics of light
transmitted through three-dimensional isotropic scattering media. The intensity
distributions measured through layers consisting of zinc oxide nanoparticles
differ significantly from the usual Rayleigh statistics associated with
speckle, and instead are in agreement with the predictions of mesoscopic
transport theory, taking into account the known material parameters of the
samples. Consistent with the measured spatial intensity fluctuations, the total
transmission fluctuates. The magnitude of the fluctuations in the total
transmission is smaller than expected on the basis of quasi-one-dimensional
(1D) transport theory, which indicates that quasi-1D theories cannot fully
describe these open three-dimensional media.Comment: 4 pages 3 figure
Exploiting speckle correlations to improve the resolution of wide-field fluorescence microscopy
Fluorescence microscopy is indispensable in nanoscience and biological
sciences. The versatility of labeling target structures with fluorescent dyes
permits to visualize structure and function at a subcellular resolution with a
wide field of view. Due to the diffraction limit, conventional optical
microscopes are limited to resolving structures larger than 200 nm. The
resolution can be enhanced by near-field and far-field super-resolution
microscopy methods. Near-field methods typically have a limited field of view
and far-field methods are limited by the involved conventional optics. Here, we
introduce a combined high-resolution and wide-field fluorescence microscopy
method that improves the resolution of a conventional optical microscope by
exploiting correlations in speckle illumination through a randomly scattering
high-index medium: Speckle correlation resolution enhancement (SCORE). As a
test, we collect two-dimensional fluorescence images of 100-nm diameter
dye-doped nanospheres. We demonstrate a deconvolved resolution of 130 nm with a
field of view of 10 x 10 \text{\mu m}^2
Field trial with oral vaccination of dogs against rabies in the Philippines
BACKGROUND: The potential role of oral vaccination of dogs against rabies in the Philippines was investigated in terms of safety and efficacy. METHODS: Prior to the vaccination campaign, a house-to-house survey was carried out to collect data on the dog population in the study area, the coastal village of Mindoro. During the vaccination campaign all households were visited again, and all dogs encountered (>2 months old) were, if possible, vaccinated. Furthermore, 14 dogs vaccinated were bled on different occasions. RESULTS: During the survey, a total of 216 dogs were counted, and none of these animals had previously been vaccinated against rabies. Only 17 dogs could be restrained and subsequently vaccinated directly by the vaccinators. Another 126 dogs were offered a local-made boiled intestine bait, containing a capsule filled with 3.0 ml SAD B19 (10(7.9) FFU/ml). The bait acceptance rate of dogs offered a bait was 96.1%. The vaccination coverage of the dog population (> 2 months old) estimated by the number of animals vaccinated directly and the number of dogs that accepted a bait and subsequently punctured the vaccine container was 76%. Fifteen and 29 days after the vaccination campaign 6 and 10 dogs (n = 14) had rabies virus neutralizing antibody titres of ≥ 0.5 IU/ml, respectively. No unintentional contacts of nontarget species, including humans, with the vaccine virus were reported. CONCLUSIONS: The results of the campaign show that oral vaccination of dogs against rabies is a promising supplementary method in dog rabies control in the Philippines
Finite-size Scaling of the Density of States in Photonic Band Gap Crystals
The famous vanishing of the density of states (DOS) in a band gap, be it
photonic or electronic, pertains to the infinite-crystal limit. In contrast,
all experiments and device applications refer to finite crystals, which raises
the question: Upon increasing the linear size of a crystal, how fast does
the DOS approach the infinite-crystal limit? We present a theory for finite
crystals that includes Bloch-mode broadening due to the presence of crystal
boundaries. Our results demonstrate that the DOS for frequencies inside a band
gap has a scale dependence for crystals in one, two and three dimensions
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