67 research outputs found
Vacuum-field-induced filamentation in laser-beam propagation
We show that filamentation initiated by quantum fluctuations is a process that limits the intensity of a laser beam that can propagate stably through a nonlinear optical medium. We also describe the experimental signatures of this process, which allow it to be distinguished from classical processes such as filamentation induced by wave-front irregularities
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
Two-Photon Interferometry for High-Resolution Imaging
We discuss advantages of using non-classical states of light for two aspects
of optical imaging: creating of miniature images on photosensitive substrates,
which constitutes the foundation for optical lithography, and imaging of micro
objects. In both cases, the classical resolution limit given by the Rayleigh
criterion is approximately a half of the optical wavelength. It has been shown,
however, that by using multi-photon quantum states of the light field, and
multi-photon sensitive material or detector, this limit can be surpassed. We
give a rigorous quantum mechanical treatment of this problem, address some
particularly widespread misconceptions and discuss the requirements for turning
the research on quantum imaging into a practical technology.Comment: Presented at PQE 2001. To appear in Special Issue of Journal of
Modern Optic
True optical spacial derivatives for plasma density measurements
This paper shows analytically and numerically that a vortex plate coupled to
a neutral density filter can deliver a true optical derivative when placed at
the focal plane of a lens pair. This technique turns spatial variations in
intensity into an intensity, which square root is the spatial derivative of the
initial intensity variation. More surprisingly, it also turns any spatial
variations in phase into an intensity, which square root is the spatial
derivative of the initial phase variation. Since the optical derivative drops
the DC component of the signal, it is possible to measure the full electron
plasma turbulence spectrum optically, without using any interferometer
Approaching the Heisenberg limit with two mode squeezed states
Two mode squeezed states can be used to achieve Heisenberg limit scaling in
interferometry: a phase shift of can be
resolved. The proposed scheme relies on balanced homodyne detection and can be
implemented with current technology. The most important experimental
imperfections are studied and their impact quantified.Comment: 4 pages, 7 figure
Agency, qualia and life: connecting mind and body biologically
Many believe that a suitably programmed computer could act for its own goals and experience feelings. I challenge this view and argue that agency, mental causation and qualia are all founded in the unique, homeostatic nature of living matter. The theory was formulated for coherence with the concept of an agent, neuroscientific data and laws of physics. By this method, I infer that a successful action is homeostatic for its agent and can be caused by a feeling - which does not motivate as a force, but as a control signal. From brain research and the locality principle of physics, I surmise that qualia are a fundamental, biological form of energy generated in specialized neurons. Subjectivity is explained as thermodynamically necessary on the supposition that, by converting action potentials to feelings, the neural cells avert damage from the electrochemical pulses. In exchange for this entropic benefit, phenomenal energy is spent as and where it is produced - which precludes the objective observation of qualia
Optical studies of gap, hopping energies and the Anderson-Hubbard parameter in the zigzag-chain compound SrCuO2
We have investigated the electronic structure of the zigzag ladder (chain)
compound SrCuO2 combining polarized optical absorption, reflection,
photoreflectance and pseudo-dielectric function measurements with the model
calculations. These measurements yield an energy gap of 1.42 eV (1.77 eV) at
300 K along (perpendicular) to the Cu-O chains. We have found that the lowest
energy gap, the correlation gap, is temperature independent. The electronic
structure of this oxide is calculated using both the
local-spin-density-approximation with gradient correction method, and the
tight-binding theory for the correlated electrons. The calculated density of
electronic states for non-correlated and correlated electrons shows
quasi-one-dimensional character. The correlation gap values of 1.42 eV
(indirect transition) and 1.88 eV (direct transition) have been calculated with
the electron hopping parameters t = 0.30 eV (along a chain), t_yz = 0.12 eV
(between chains) and the Anderson-Hubbard repulsion on copper sites U= 2.0 eV.
We concluded that SrCuO_2 belongs to the correlated-gap insulators.Comment: 24 pages, 8 figures, to be published in Phys.Rev.
Neuroblastoma presenting with symptoms of epidural compression at birth: a case report
Insights into the Molecular Mechanisms of the Anti-Atherogenic Actions of Flavonoids in Normal and Obese Mice
Obesity is a major and independent risk factor for cardiovascular disease and it is strongly associated with the development of dyslipidemia, insulin resistance and type 2 diabetes. Flavonoids, a diverse group of polyphenol compounds of plant origin widely distributed in human diet, have been reported to have numerous health benefits, although the mechanisms underlying these effects have remained obscure. We analyzed the effects of chronic dietary supplementation with flavonoids extracted from cranberry (FLS) in normal and obese C57/BL6 mice compared to mice maintained on the same diets lacking FLS. Obese mice supplemented with flavonoids showed an amelioration of insulin resistance and plasma lipid profile, and a reduction of visceral fat mass. We provide evidence that the adiponectin-AMPK pathway is the main mediator of the improvement of these metabolic disorders. In contrast, the reduced plasma atherogenic cholesterol observed in normal mice under FLS seems to be due to a downregulation of the hepatic cholesterol synthesis pathway. Overall, we demonstrate for the first time that the molecular mechanisms underlying the beneficial effects of flavonoids are determined by the metabolic state
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