# Journal of Optics

Published by IOP Publishing

Online ISSN: 2040-8986

Print ISSN: 2040-8978

Published by IOP Publishing

Online ISSN: 2040-8986

Print ISSN: 2040-8978

Publications

In this paper, we demonstrate a high speed spectral domain optical coherence tomography (SDOCT) system capable of achieving full range complex imaging at 47 kHz line scan rate. By applying beam-offset method, a constant modulation frequency is introduced into each B-scan that enables reconstruction of the full range complex SDOCT images of in vivo tissue samples. To make use of the full capacity of detection camera used in the system, system control software is developed that streams the raw spectral fringe data directly into the computer memory. In order to assess performance of the high speed full range SDOCT system for imaging biological specimen, we present results imaged from the cuticle of fingernail of a human volunteer in vivo, and from the chicken embryos ex vivo. We also show the high sensitivity advantages of full range complex imaging as compared to the conventional SDOCT. To the best of our knowledge, 47,000 A-scan imaging rate is the highest imaging rate ever been reported for full range complex imaging. Notwithstanding, the method reported here has no limitations on the imaging speed, thus offers a useful tool to achieve volumetric imaging of living samples where the high sensitivity region around zero-delay line in the system can be utilized for imaging.

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We show that laser-tweezers Raman spectroscopy of eukaryotic cells with a significantly larger diameter than the tight focus of a single beam laser trap leads to optical trapping of the cell by its optically densest part, i.e. typically the cell's nucleus. Raman spectra of individual optically trapped monocytes are compared with location-specific Raman spectra of monocytes adhered to a substrate. When the cell's nucleus is stained with a fluorescent live cell stain, the Raman spectrum of the DNA-specific stain is observed only in the nucleus of individual monocytes. Optically trapped monocytes display the same behavior. We also show that the Raman spectra of individual monocytes exhibit the characteristic Raman signature of cells that have not yet fully differentiated and that individual primary monocytes can be distinguished from transformed monocytes based on their Raman spectra. This work provides further evidence that laser tweezers Raman spectroscopy of individual cells provides meaningful biochemical information in an entirely nondestructive fashion that permits discerning differences between cell types and cellular activity.

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Polarized light microscopy provides unique opportunities for analyzing the molecular order in man-made and natural materials, including biological structures inside living cells, tissues, and whole organisms. 20 years ago, the LC-PolScope was introduced as a modern version of the traditional polarizing microscope enhanced by liquid crystal devices for the control of polarization, and by electronic imaging and digital image processing for fast and comprehensive image acquisition and analysis. The LCPolScope is commonly used for birefringence imaging, analyzing the spatial and temporal variations of the differential phase delay in ordered and transparent materials. Here we describe an alternative use of the LC-PolScope for imaging the polarization dependent transmittance of dichroic materials. We explain the minor changes needed to convert the instrument between the two imaging modes, discuss the relationship between the quantities measured with either instrument, and touch on the physical connection between refractive index, birefringence, transmittance, diattenuation, and dichroism.

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This paper presents a planar waveguide grating sensor integrated with a photodetector (PD) for on-chip optical sensing systems which are suitable for diagnostics in the field and in-situ measurements. III-V semiconductor-based thin-film PD is integrated with a polymer based waveguide grating device on a silicon platform. The fabricated optical sensor successfully discriminates optical spectral characteristics of the polymer waveguide grating from the on-chip PD. In addition, its potential use as a refractive index sensor is demonstrated. Based on a planar waveguide structure, the demonstrated sensor chip may incorporate multiple grating waveguide sensing regions with their own optical detection PDs. In addition, the demonstrated processing is based on a post-integration process which is compatible with silicon complementary metal-oxide semiconductor (CMOS) electronics. Potentially, this leads a compact, chip-scale optical sensing system which can monitor multiple physical parameters simultaneously without need for external signal processing.

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Malaria affects over 200 million individuals annually, resulting in 800,000 fatalities. Current tests use blood smears and can only detect the disease when 0.1-1% of blood cells are infected. We are investigating the use of photoacoustic flowmetry to sense as few as one infected cell among 10 million or more normal blood cells, thus diagnosing infection before patients become symptomatic. Photoacoustic flowmetry is similar to conventional flow cytometry, except that rare cells are targeted by nanosecond laser pulses to induce ultrasonic responses. This system has been used to detect single melanoma cells in 10 ml of blood. Our objective is to apply photoacoustic flowmetry to detection of the malaria pigment hemozoin, which is a byproduct of parasite-digested hemoglobin in the blood. However, hemozoin is difficult to purify in quantities greater than a milligram, so a synthetic analog, known as β-hematin was derived from porcine haemin. The specific purpose of this study is to establish the efficacy of using β-hematin, rather than hemozoin, for photoacoustic measurements. We characterized β-hematin using UV-vis spectroscopy, TEM, and FTIR, then tested the effects of laser irradiation on the synthetic product. We finally determined its absorption spectrum using photoacoustic excitation. UV-vis spectroscopy verified that β-hematin was distinctly different from its precursor. TEM analysis confirmed its previously established nanorod shape, and comparison of the FTIR results with published spectroscopy data showed that our product had the distinctive absorbance peaks at 1661 and 1206 cm(-1). Also, our research indicated that prolonged irradiation dramatically alters the physical and optical properties of the β-hematin, resulting in increased absorption at shorter wavelengths. Nevertheless, the photoacoustic absorption spectrum mimicked that generated by UV-vis spectroscopy, which confirms the accuracy of the photoacoustic method and strongly suggests that photoacoustic flowmetry may be used as a tool for diagnosis of malaria infection.

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The article encloses a new Fourier space method for rigorous optical
simulation of 3D periodic dielectric structures. The method relies upon
rigorous solution of Maxwell's equations in complex composite structures by the
Generalized Source Method. Extremely fast GPU enabled calculations provide a
possibility for an efficient search of eigenmodes in 3D periodic complex
structures on the basis of rigorously obtained resonant electromagnetic
response. The method is applied to the homogenization problem demonstrating a
complete anisotropic dielectric tensor retrieval.

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We investigate the differences in the dynamics of the ultrafast photo-induced
metal-insulator transition (MIT) of two VO$_2$ thin films deposited on
different substrates, TiO$_2$ and Al$_2$O$_3$, and in particular the
temperature dependence of the threshold laser fluence values required to induce
various MIT stages in a wide range of sample temperatures (150 K - 320 K). We
identified that, although the general pattern of MIT evolution was similar for
the two samples, there were several differences. Most notably, the threshold
values of laser fluence required to reach the transition to a fully metallic
phase in the VO$_2$ film on the TiO$_2$ substrate were nearly constant in the
range of temperatures considered, whereas the VO$_2$/Al$_2$O$_3$ sample showed
clear temperature dependence. Our analysis qualitatively connects such behavior
to the structural differences in the two VO$_2$ films.

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We present an analysis of self-imaging in a regime beyond the paraxial, where
deviation from simple paraxial propagation causes apparent self-imaging
aberrations. The resulting structures are examples of aberration without rays
and are described analytically using post-paraxial theory. They are shown to
relate to, but surprisingly do not precisely replicate, a standard integral
representation of a diffraction cusp. Beyond the Talbot effect, this result is
significant as it illustrates that the effect of aberration -- as manifested in
the replacement of a perfect focus with a cusp-like pattern -- can occur as a
consequence of improving the paraxial approximation, rather than due to
imperfections in the optical system.

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We investigate the capabilities of the effective non-retarded method (ENR) to
explore and design nanoparticles composites with specific optical properties.
We consider a composite material comprising periodically distributed metallic
spheres in a dielectric host matrix. The effective macroscopic dielectric
function of the composite medium is obtained by means of the ENR and is used to
calculate the electromagnetic response of a slab made of such an inhomogeneous
material. This response is compared with that obtained using the
Korringa-Kohn-Rostoker wave calculation method (KKR). We analyze the optical
properties for different filling fractions, especially in the vicinity of the
resonance frequencies of the macroscopic dielectric function. We show that
appropriately choosing the parameters of the composite it is possible to
achieve a tunable absorber film. The ENR results to be a versatile tool for the
design of nanoparticle composite materials with specific properties.

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We propose to achieve a strong bistable response of a thin layer of a
saturable absorption medium by involving a planar metamaterial specially
designed to bear a high-Q trapped-mode resonance in the infrared region.

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The optical absorption properties of graphene wrapped dielectric particles
have been investigated by using Mie scattering theory and exact
multi-scattering method. It is shown that subwavelength strong absorption in
infrared spectra can take place in such systems due to the excitation of
plasmon resonance in graphene. The absorption characteristics and efficiency
are tunable by varying Fermi level and damping constant of graphene, or by
changing size and dielectric constant of small particles. For a cluster of
these particles, the absorption characteristics are also affected by the
separation distance between them. These extreme light resonances and
absorptions in graphene wrapped nanostructures have great potential for
opto-electronic devices.

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An exact solution of the Maxwell equations in Rindler coordinates is
obtained. The electromagnetic field represents a wave preserving its shape in a
relativistic uniformly accelerated frame. The relation with Airy beams is shown
explicitly in the non-relativistic limit.

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We present a contrast-maximizing optimal linear representation of
polarimetric images obtained from a snapshot polarimetric camera for enhanced
vision of a polarized light source in obscured weather conditions (fog, haze,
cloud) over long distances (above 1 km). We quantitatively compare the gain in
contrast obtained by different linear representations of the experimental
polarimetric images taken during rapidly varying foggy conditions. It is shown
that the adaptive image representation that depends on the correlation in
background noise fluctuations in the two polarimetric images provides an
optimal contrast enhancement over all weather conditions as opposed to a simple
difference image which underperforms during low visibility conditions. Finally,
we derive the analytic expression of the gain in contrast obtained with this
optimal representation and show that the experimental results are in agreement
with the assumed correlated Gaussian noise model.

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We experimentally demonstrate a broadband and an ultra-broadband spectral
bandwidth polarization rotators. Both polarization rotators have modular
design, that is, they are comprised of an array of half-wave plates rotated to
a given angle. We show that the broadband and ultra-broadband performance of
the polarization rotators is due to the adiabatic nature of the light
polarization evolution. In this paper we experimentally investigate the
performance of broadband and ultra-broadband polarization rotators comprising
of ten multi-order half-wave plates or ten commercial achromatic half-wave
plates, respectively. The half-wave plates in the arrays are rotated gradually
with respect to each other starting from an initial alignment between the fast
polarization axis of the first one and the incoming linearly polarized light,
to the desired polarization rotation angle.

…

The Alcubierre spacetime was simulated by means of a Tamm medium which is
asymptotically identical to vacuum and has constitutive parameters which are
ontinuous functions of the spatial coordinates. Accordingly, the Tamm medium is
amenable to physical realization as a nanostructured metamaterial. A
comprehensive characterization of ray trajectories in the Tamm medium was
undertaken, within the geometric-optics regime. Propagation directions
corresponding to evanescent waves were identified: these occur in the region of
the Tamm medium which corresponds to the warp bubble of the Alcubierre
spacetime, especially for directions perpendicular to the velocity of the warp
bubble at high speeds of that bubble. Ray trajectories are acutely sensitive to
the magnitude and direction of the warp bubble's velocity, but rather less
sensitive to the thickness of the transition zone between the warp bubble and
its background. In particular, for rays which travel in the same direction as
the warp bubble, the latter acts as a focusing lens, most notably at high
speeds.

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We design non-singular cloaks enabling objects to scatter waves like objects with smaller size and very different shapes. We consider the Schrodinger equation which is valid e.g. in the contexts of geometrical and quantum optics. More precisely, we introduce a generalized non-singular transformation for star domains, and numerically demonstrate that an object of nearly any given shape surrounded by a given cloak scatters waves in exactly the same way as a smaller object of another shape. When a source is located inside the cloak, it scatters waves as if it would be located some distance away from a small object. Moreover, the invisibility region actually hosts almost-trapped eigenstates. Mimetism is numerically shown to break down for the quantified energies associated with confined modes. If we further allow for non-isomorphic transformations, our approach leads to the design of quantum super-scatterers: a small size object surrounded by a quantum cloak described by a negative anisotropic heterogeneous effective mass and a negative spatially varying potential scatters matter waves like a larger nano-object of different shape. Potential applications might be for instance in quantum dots probing. Comment: Version 2: 23 pages, 9 figures. More figures added. Misprints corrected. OCIS Codes: (000.3860) Mathematical methods in physics; (260.2110) Electromagnetic theory; (160.3918) Metamaterials; (160.1190) Anisotropic optical materials; (350.7420) Waves; (230.1040) Acousto-optical devices; (160.1050) Acousto-optical materials; (290.5839) Scattering,invisibility; (230.3205) Invisibility cloaks

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We study paraxial beam propagation parallel to the screw axis of a dislocated
amorphous medium that is optically weakly inhomogeneous and isotropic. The
effect of the screw dislocation on the beam's orbital angular momentum is shown
to change the optical vortex strength, rendering vortex annihilation or
generation possible. Furthermore, the dislocation is shown to induce a weak
\textit{biaxial} anisotropy in the medium due to the elasto-optic effect, which
changes the beam's spin angular momentum as well as causing precession of the
polarization. We derive the equations of motion of the beam and demonstrate the
optical Hall effect in the dislocated medium. Its application with regard to
determining the Burgers vector as well as the elasto-optic coefficients of the
medium is explained.

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Nanoplasmonics has recently experienced explosive development with many novel ideas and dramatic achievements in both fundamentals and applications. The spaser has been predicted and observed experimentally as an active element -- generator of coherent local fields. Even greater progress will be achieved if the spaser could function as a ultrafast nanoamplifier -- an optical counterpart of the MOSFET (metal-oxide-semiconductor field-effect transistor). A formidable problem with this is that the spaser has the inherent feedback causing quantum generation of nanolocalized surface plasmons and saturation and consequent elimination of the net gain, making it unsuitable for amplification. We have overcome this inherent problem and shown that the spaser can perform functions of an ultrafast nanoamplifier in two modes: transient and bistable. On the basis of quantum density matrix (optical Bloch) equations we have shown that the spaser amplifies with gain greater than 50, the switching time less or on the order of 100 fs (potentially, 10 fs). This prospective spaser technology will further broaden both fundamental and applied horizons of nanoscience, in particular, enabling ultrafast microprocessors working at 10 to 100 THz clock speed. Other prospective applications are in ultrasensing, ultradense and ultrafast information storage, and biomedicine. The spasers are based on metals and, in contrast to semiconductors, are highly resistive to ionizing radiation, high temperatures, microwave radiation, and other adverse environments. Comment: 4 figures

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We investigated the effct of pump wavelength on the modal instabilities (MI)
in high power linearly-polarized Yb-doped fiber amplifiers. We built a novel
semi-analytical model to determine the frequency coupling characteristics and
power threshold of MI, which indicates promising MI suppression through pumping
at an appropriate wavelength. By pumping at 915nm, the threshold can be
enhanced by a factor of 2.36 as compared to that pumped at 976nm. Based on a
high power linearly-polarized fiber amplifier platform, we studied the
influence of pump wavelength experimentally. The threshold has been increased
by a factor of 2 at 915nm, which agrees with the theoretical calculation and
verified our theoretical model. Furthermore, we show that MI suppression by
detuning the pump wavelength is weakened for fiber with large core-to-cladding
ratio.

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We present an analytical model for describing complex dynamics of a hybrid
system consisting of interacting classical and quantum resonant structures.
Classical structures in our model correspond to plasmonic nano-resonators of
different geometries, as well as other types of nano- and micro-structures
optical response of which can be described without invoking quantum-mechanical
treatment. Quantum structures are represented by atoms or molecules, or their
aggregates (for example, quantum dots and carbon nanotubes), which can be
accurately modelled only with the use of quantum approach. Our model is based
on the set of equations that combines well-established density matrix formalism
appropriate for quantum systems, coupled with harmonic-oscillator equations
ideal for modelling sub-wavelength plasmonic and optical resonators. This model
can also be straightforwardly adopted for describing electromagnetic dynamics
of various hybrid systems outside the photonics realm, such as
Josephson-junction metamaterials, or SQUID elements coupled with an RF strip
resonator.

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The investigation of surface termination over the inverse Goos-H\"anchen (GH)
shift of two-dimensional (2D) negatively refractive photonic crystal (NRPhC),
made by air holes arranged in hexagonal lattice in a dielectric background,
shows that the magnitude of the inverse GH shift of 2D-NRPhC depends strongly
on the surface termination even for an incident beam with fixed frequency and
incidence angle, while the effective index of 2D-NRPhC remains. For surface
termination with the outmost row of air holes complete, TM-polarized light is
characterized by the inverse GH shift of more than tens of lattices and
TE-polarized light by very tiny inverse GH shift. While for surface termination
with the outmost row of air holes cut in quarter or so, the situation is just
on the opposite. In addition, the reflectivity of 2D-NRPhC as a function of
surface termination is also studied, and the result shows that the smaller the
reflectivity the larger the inverse GH shifts. The results of this paper will
provide technical information for the combination of various functional
photonic elements in the design of integrated optical circuits.

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It is shown that the photon picture of the electromagnetic field enables one
to determine unambiguously the splitting of the total angular momentum of the
electromagnetic field into the orbital part and the spin part.

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The law of reflection and Snell's law are among the tenets of geometrical
optics. Corrections to these laws in wave optics are respectively known as the
angular Goos-Hänchen shift and Fresnel filtering. In this paper we give a
positive answer to the question of whether the two effects are common in nature
and we study both effects in the more general context of optical beam shifts.
We find that both effects are caused by the same principle, but have been
defined differently. We identify and discuss the similarities and differences
that arise from the different definitions.

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We prove that a single photon with quantum data encoded in its orbital angular
momentum can be manipulated with simple optical elements to provide any desired
quantum computation. We will show how to build any quantum unitary operator using
beamsplitters, phase shifters, holograms and an extraction gate based on quantum
interrogation. The advantages and challenges of these approach are then discussed, in
particular the problem of the readout of the results.

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This paper is devoted to study the propagation of light beams carrying
orbital angular momentum in optically anisotropic media. We first review some
properties of homogeneous anisotropic media, and describe how the paraxial
formalism is modified in order to proceed with a new approach dealing with a
general setting of paraxial propagation along uniaxial inhomogeneous media.
This approach is suitable for describing the space-variant-optical-axis phase
plates.

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We predict a non-thermal magneto-optical effect for magnetic insulators
subject to intense light carrying orbital angular momentum (OAM). Using a
classical approach to second harmonic generation in non-linear media with
specific symmetry properties we predict a significant nonlinear contribution to
the local magnetic field triggered by light with OAM. The resulting magnetic
field originates from the displacement of electrons driven by the electrical
field (with amplitude $E_0$) of the spatially inhomogeneous optical pulse,
modeled here as a Laguerre-Gaussian beam carrying OAM. In particular, the
symmetry properties of the irradiated magnet allow for magnetic field responses
which are second-order ($\sim E_0^2$) and fourth-order ($\sim E_0^4$) in
electric-field strength and have opposite signs. For sufficiently high laser
intensities, terms $\sim E_0^4$ dominate and generate magnetic field strengths
which can be as large as several Tesla. Moreover, changing the OAM of the laser
beam is shown to determine the direction of the total light-induced magnetic
field, which is further utilized to study theoretically the non-thermal
magnetization dynamics.

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In this paper we describe how to derive the expressions for the higher
nonlinear generation of waves, their transmission and reflection for the case
of a normal incidence plane wave by direct superposition of nonlinear dipoles.
We describe explicitly that the transmitted and reflected nonlinear harmonic
wave can only propagate inside the material if the phase matching condition is
fulfilled and show for the case of second-harmonic-generation that our
calculation yields similar results with coupled-mode-theory (CMT).

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We experimentally study the writing of one- and two-dimensional
photorefractive lattices and the propagation of linear and nonlinear waves
inside them. Using plane waves, we perform a time-resolved study of lattice
writing and find good agreement with transient and steady-state photorefractive
theory. In particular, the ratio of the drift to diffusion terms is
proportional to the lattice period. We then analyze various wave propagation
schemes. For focussed linear waves with broad transverse spectrum, we note that
both the intensity distributions in real space ("discrete diffraction") and
Fourier space ("Brillouin zone spectroscopy") reflect the Bragg planes and band
structure. For non-linear waves, we observe modulational instability and
time-domain discrete solitons formation. We discuss also the non-ideal effects
inherent to the photo-induction technique : anisotropy, parasitic nonlinearity,
diffusive term, and non-stationarity.

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We have introduced a class of spiraling elliptic breathers in saturable
nonlinear media with linear anisotropy. Two kinds of evolution behaviors of the
breathers, rotating and pendulum-like librating, are both predicted by the
variational approach, and confirmed by the numerical simulation.The spiraling
elliptic breathers can rotate even though they have no initial orbital angular
momentum (OAM). Due to the linear anisotropy of the media, the OAM is no longer
conserved. Therefore, the angular velocity is found to be not a constant but a
periodic function of the propagation distance. When the linear anisotropy is
large enough, the spiraling elliptic breathers can librate like the pendulum.
The spiraling elliptic breathers exist in the media with not only the saturable
nonlinearity but also the nonlocal nonlinearity, as a matter of fact, they are
universal in the nonlinear media with the linear anisotropy.

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Results of research of resonant phenomena in planar periodic structures
consisted of dielectric elements are presented. A problem of plane wave
diffraction by a structure which a periodic cell is composed of two dielectric
bars with different lengths has been solved. For the first time an existence of
high Q-factor trapped mode resonances are revealed in these structures. The
main difference of studied structure in contrast to the planar structure with a
single dielectric bar in the unit cell is appearing of a great red shift of a
trapped mode resonant wavelength. The red shift is caused by strong coupling of
electromagnetic fields in neighbor dielectric bar resonators. This property is
very attractive to design resonant periodic planar structures by using moderate
refractive index materials like semiconductors within their transparency
window. In the near infrared band, the trapped mode resonances of periodic
planar structure with bars made of germanium have been studied. It is shown
that decreasing of structure asymmetry degree results in increasing of both red
shift and Q-factor of resonance.

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We present a theory of the local field corrections to the spontaneous
emission rate for the array of silicon nanocrystals in silicon dioxide. An
analytical result for the Purcell factor is obtained. We demonstrate that the
local-field corrections are sensitive to the volume fill factor of the
nanocrystals in the sample and are suppressed for large values of the fill
factor. The local-field corrections and the photonic density of states are
shown to be described by two different effective permittivities: the harmonic
mean between the nanocrystal and the matrix permittivities and the
Maxwell-Garnett permittivity.

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We have studied harmonic oscillations in an elliptical optical waveguide
array in which the coupling between neighboring waveguides is varied in accord
with a Kac matrix so that the propagation constant eigenvalues can take equally
spaced values. As a result, long-living Bloch oscillation (BO) and dipole
oscillation (DO) are obtained when a linear gradient in the propagation
constant is applied. Moreover, we achieve a switching from DO to BO or vice
versa by ramping up the gradient profile. The various optical oscillations as
well as their switching are investigated by field evolution analysis and
confirmed by Hamiltonian optics. The equally spaced eigenvalues in the
propagation constant allow viable applications in transmitting images,
switching and routing of optical signals.

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We show that second harmonic generation can be enhanced by Fano resonant
coupling of asymmetric plasmonic metal nanostructures. We develop a theoretical
model examining the effects of electromagnetic interaction between two metal
nanostructures on the second harmonic generation. We compare the second
harmonic generation efficiency of a single plasmonic metal nanostructure with
that of two coupled ones. We show that second harmonic generation from a single
metal nanostructure can be enhanced about 30 times by attaching a second metal
nanostructure with a 10 times higher quality factor than that of the first one.
The origin of this enhancement is Fano resonant coupling of the two metal
nanostructures. We support our findings on Fano enhancement of second harmonic
generation by an experimental study of a coupled plasmonic system composed of a
silver nanoparticle and a silver nanowire on glass surface in which the ratio
of the quality factors are also estimated to be around 10 times.

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We study a critically coupled cavity doped with resonant atoms with
metamaterial slabs as mirrors. We show how resonant atom-cavity interaction can
lead to a splitting of the critical coupling dip. The results are explained in
terms of the frequency and lifetime splitting of the coupled system.

…

We investigate the self-Kerr nonlinearity of a four-level N-type atomic
system in 87Rb and observe its reversible property with the unidirectional
increase of the switching field. For the laser arrangement that the probe field
interacts with the middle two states, the slope and the sign of the self-Kerr
nonlinearity around the atomic resonance can not only be changed from negative
to positive, but also can be changed to negative again with the unidirectional
increasing of the switching field. Numerical simulation agrees very well with
the experimental results and dressed state analysis is presented to explain the
experimental results.

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The interference between optical beams of different polarizations plays a
fundamental role in reproducing the optical analog of the electron spin weak
measurement. The extraordinary point in optical weak measurements is
represented by the possibility to estimate with great accuracy the
Goos-Haenchen (GH) shift by measuring the distance between the peak of the
outgoing beams for two opposite rotation angles of the polarizers located
before and after the dielectric block. Starting from the numerical calculation
of the GH shift, which clearly shows a frequency crossover for incidence near
to the critical angle, we present a detailed study of the interference between
s and p polarized waves in the critical region. This allows to determine in
which conditions it is possible to avoid axial deformations and reproduce the
GH curves. In view of a possible experimental implementation, we give the
expected weak measurement curves for Gaussian lasers of different beam waist
sizes propagating through borosilicate (BK7) and fused silica dielectric
blocks.

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Blue-green historical beads are sometimes referred to as instable ones because of their degradability. At present, the cause of the phenomenon of deterioration of the blue-green beads is unknown. We explore internal microstucture of degrading blue-green historical beads and its evolution in the process of bead deterioration. Investigating transmittance and scattering spectra of visible and near infrared light we observe formation of microscopic internal inhomogeneities with the sizes less than 150 nm in the glass bulk and growth of their density with increase in degree of bead degradation. By means of laser scanning microscopy we also observe numerous microinclusions and microcracks on the cleavage surface of a partially degraded bead. We discuss possible physical factors resulting in destruction of the blue-green beads.

…

We investigate the influence of the phase-front curvature of an input light
beam on the transverse localization of light by choosing an evanescently
coupled disordered one-dimensional semi-infinite waveguide lattice as an
example. Our numerical study reveals that a finite phase front curvature of the
input beam indeed plays an important role and it could degrade the quality of
light localization in a disordered dielectric structure. More specifically, a
faster transition from ballistic mode of beam propagation due to diffraction to
a characteristic localized state is observed in case of a continuous wave (CW)
beam, whose phase-front is plane as compared to one having a curved phase
front.

…

We present a study of radially and azimuthally polarized Bessel-Gauss beams
in both the paraxial and nonparaxial regimes. We discuss the validity of the
paraxial approximation and the form of the nonparaxial corrections for
Bessel-Gauss beams. We show that, independently from the ratio between the
Bessel aperture cone angle $\vartheta_0$ and the Gauss beam divergence
$\theta_0$, the nonparaxial corrections are always very small and therefore
negligible. Explicit expressions for the nonparaxial vector electric field
components are also reported.

…

We study monochromatic, scalar solutions of the Helmholtz and paraxial wave
equations from a field-theoretic point of view. We introduce appropriate
time-independent Lagrangian densities for which the Euler-Lagrange equations
reproduces either Helmholtz and paraxial wave equations with the
$z$-coordinate, associated with the main direction of propagation of the
fields, playing the same role of time in standard Lagrangian theory. For both
Helmholtz and paraxial scalar fields, we calculate the canonical
energy-momentum tensor and determine the continuity equations relating "energy"
and "momentum" of the fields. Eventually, the reduction of the Helmholtz wave
equation to a useful first-order Dirac form, is presented. This work sheds some
light on the intriguing and not so acknowledged connections between angular
spectrum representation of optical wavefields, cosmological models and physics
of black holes.

…

This work is the second part of an investigation aiming at the study of
optical wave equations from a field-theoretic point of view. Here, we study
classical and quantum aspects of scalar fields satisfying the paraxial wave
equation. First, we determine conservation laws for energy, linear and angular
momentum of paraxial fields in a classical context. Then, we proceed with the
quantization of the field. Finally, we compare our result with the traditional
ones.

…

We consider two-dimensional (2D) localized vortical modes in the three-wave
system with the quadratic ($\chi ^{(2)}$) nonlinearity, alias nondegenerate
second-harmonic-generating system, guided by the isotropic harmonic-oscillator
(HO) (alias parabolic) confining potential. In addition to the straightforward
realization in optics, the system models mixed atomic-molecular Bose-Einstein
condensates (BECs). The main issue is stability of the vortex modes, which is
investigated through computation of instability growth rates for eigenmodes of
small perturbations, and by means of direct simulations. The threshold of
parametric instability for single-color beams, represented solely by the second
harmonic (SH) with zero vorticity, is found in an analytical form with the help
of the variational approximation (VA). Trapped states with vorticities $\left(
+1,-1,0\right) $ in the two fundamental-frequency (FF) components and the SH
one [the so-called \textit{hidden-vorticity} (HV) modes] are completely
unstable. Also unstable are \textit{semi-vortices} (SVs), with component
vorticities $% \left( 1,0,1\right) $. However, full vortices, with charges
$\left( 1,1,2\right) $, have a well-defined stability region. Unstable full
vortices feature regions of robust dynamical behavior, where they periodically
split and recombine, keeping their vortical content.

…

We review optical phenomena associated with the internal energy
redistribution which accompany propagation and transformations of monochromatic
light fields in homogeneous media. The total energy flow (linear-momentum
density, Poynting vector) can be divided into spin part associated with the
polarization and orbital part associated with the spatial inhomogeneity. We
give general description of the internal flows in the coordinate and momentum
(angular spectrum) representations for both nonparaxial and paraxial fields.
This enables one to determine local densities and integral values of the spin
and orbital angular momenta of the field. We analyse patterns of the internal
flows in standard beam models (Gaussian, Laguerre-Gaussian, flat-top beam,
etc.), which provide an insightful picture of the energy transport. The
emphasize is made to the singular points of the flow fields. We describe the
spin-orbit and orbit-orbit interactions in the processes of beam focusing and
symmetry breakdown. Finally, we consider how the energy flows manifest
themselves in the mechanical action on probing particles and in the
transformations of a propagating beam subjected to a transverse perturbation.

…

I present theoretical calculations of reflection beamshifts, Goos-H\"anchen
and Imbert-Fedorov shifts, due to the presence of a monolayer graphene on a
dielectric media when using a beam with wavelength in the visible range.
Specifically, I look at beamshifts for different polarization states (p, s,
$45^0$, $\sigma^+$). The Goos-H\"anchen shifts I calculated are in good
agreement with results of a recent experiment. I will discuss other possible
experimental routes to determine beamshifts in graphene.

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We present a formalism able to predict the transformation of light beams
passing through biaxial crystals. We use this formalism to show both
theoretically and experimentally the transition from double refraction to
conical refraction, which is found when light propagates along one of the optic
axes of a biaxial crystal. Additionally, we demonstrate that the theory is
applicable both to non-cylindrically symmetric and non-homogeneously polarized
beams by predicting the transformation of input beams passing through a cascade
of biaxial crystals.

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Omnidirectional light concentration remains an unsolved problem despite such
important practical applications as design of efficient mobile photovoltaic
cells. Optical black hole designs developed recently offer partial solution to
this problem. However, even these solutions are not truly omnidirectional since
they do not exhibit a horizon, and at large enough incidence angles light may
be trapped into quasi-stationary orbits around such imperfect optical black
holes. Here we propose and realize experimentally another gravity-inspired
design of a broadband omnidirectional light concentrator based on the
cosmological Big Crunch solutions. By mimicking the Big Crunch spacetime via
corresponding effective optical metric we make sure that every photon world
line terminates in a single point.

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We describe a technique to produce narrow-band photon pairs with
frequency-bin entanglement, whose relative phase can be tuned using linear
polarization optics. We show that, making use of the polarization-frequency
coupling effect, the phase of a complex polarizer can be transferred into the
frequency entanglement.

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For the purpose of a pedagogical introduction to the spatial aspects of
Spontaneous Parametric Downconversion (SPDC), we present here a detailed
first-principles derivation of the transverse correlation width of photon pairs
in degenerate collinear SPDC. Along the way, we discuss the quantum-optical
calculation of the amplitude for the SPDC process, as well as its simplified
form for nearly collinear degenerate phase matching. Following this, we show
how this biphoton amplitude can be approximated with a Double-Gaussian
wavefunction, give a brief discussion of the statistics of such Double-Gaussian
distributions, and show how such approximations allow a simple description of
the biphoton field over propagation. Next, we use this Double-Gaussian
approximation to get a simplified estimation of the transverse correlation
width, and compare it to more accurate calculations as well as experimental
results. We then conclude with a discussion of the related concept of a
biphoton birth zone, using it to develop intuition for the tradeoff between the
first-order spatial coherence and bipohoton correlations in SPDC.

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In spontaneous parametric down-conversion photons are known to be created
coherently and with equal probability over the entire length of the crystal.
Then, there is no particular position in the crystal where a photon pair is
created. We make the seemingly contradictory observation that we can control
the time delay with the crystal position along the propagation direction. We
resolve this contradiction by showing that the spatio-temporal correlations
critically affect the temporal properties of the pair of photons, when using a
finite detector size. We expect this to have important implications for
experiments that require indistinguishable photons.

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We analyse a multilayer leaky cladding (MLC) fibre using the finite element method and study the effect of the MLC on the bending loss and birefringence of two types of structures: (i) a circular core large-mode-area structure and (ii) an elliptical-small-core structure. In a large-mode-area structure, we verify that the multilayer leaky cladding strongly discriminates against higher order modes to achieve single-mode operation, the fibre shows negligible birefringence, and the bending loss of the fibre is low for bending radii larger than 10 cm. In the elliptical-small-core structure we show that the MLC reduces the birefringence of the fibre. This prevents the structure from becoming birefringent in case of any departures from circular geometry. The study should be useful in the designs of MLC fibres for various applications including high power amplifiers, gain flattening of fibre amplifiers and dispersion compensation. Comment: 18 pages

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