83 research outputs found
Dispersive properties of quasi-phase-matched optical parametric amplifiers
The dispersive properties of non-degenerate optical parametric amplification
in quasi-phase-matched (QPM) nonlinear quadratic crystals with an arbitrary
grating profile are theoretically investigated in the no-pump-depletion limit.
The spectral group delay curve of the amplifier is shown to be univocally
determined by its spectral power gain curve through a Hilbert transform. Such a
constraint has important implications on the propagation of spectrally-narrow
optical pulses through the amplifier. In particular, it is shown that anomalous
transit times, corresponding to superluminal or even negative group velocities,
are possible near local minima of the spectral gain curve. A possible
experimental observation of such effects using a QPM Lithium-Niobate crystal is
suggested.Comment: submitted for publicatio
Co-axial dual-core resonant leaky fibre for optical amplifiers
We present a co-axial dual-core resonant leaky optical fibre design, in which
the outer core is made highly leaky. A suitable choice of parameters can enable
us to resonantly couple power from the inner core to the outer core. In a
large-core fibre, such a resonant coupling can considerably increase the
differential leakage loss between the fundamental and the higher order modes
and can result in effective single-mode operation. In a small-core single-mode
fibre, such a coupling can lead to sharp increase in the wavelength dependent
leakage loss near the resonant wavelength and can be utilized for the
suppression of amplified spontaneous emission and thereby gain equalization of
an optical amplifier. We study the propagation characteristics of the fibre
using the transfer matrix method and present an example of each, the
large-mode-area design for high power amplifiers and the wavelength tunable
leakage loss design for inherent gain equalization of optical amplifiers.Comment: 6 page
Wave-front engineering by Huygens-Fresnel principle for nonlinear optical interactions in domain engineered structures
The wave-front engineering for nonlinear optical interactions was discussed.
Using Huygens-Fresnel principle we developed a general theory and technique for
domain engineering with conventional quasi-phase-matching structures being the
special cases. By Fourier analysis we put forward the concept of local
quasi-phase matching, which suggests that the quasi-phase matching is fulfilled
only locally not globally. Experiments on focal effect of second-harmonic wave
agreed well with the theoretical prediction. The proposed scheme combines three
optical functions: generation, focusing and beam splitting of second-harmonic
wave, thus making the device more compact. Further the proposed scheme can be
used to perform the integration of multi-functional optical properties in
nonlinear photonics, as well as expand the use of nonlinear optical devices.Comment: 15 pages, 3 figure
Engineered nonlinear lattices
We show that with the quasi-phase-matching technique it is possible to fabricate stripes of nonlinearity that trap and guide light like waveguides. We investigate an array of such stripes and find that when the stripes are sufficiently narrow, the beam dynamics is governed by a quadratic nonlinear discrete equation. The proposed structure therefore provides an experimental setting for exploring discrete effects in a controlled manner. In particular, we show propagation of breathers that are eventually trapped by discreteness. When the stripes are wide the beams evolve in a structure we term a quasilattice, which interpolates between a lattice system and a continuous system.Peer ReviewedPostprint (published version
Entangled-Photon Generation from Parametric Down-Conversion in Media with Inhomogeneous Nonlinearity
We develop and experimentally verify a theory of Type-II spontaneous
parametric down-conversion (SPDC) in media with inhomogeneous distributions of
second-order nonlinearity. As a special case, we explore interference effects
from SPDC generated in a cascade of two bulk crystals separated by an air gap.
The polarization quantum-interference pattern is found to vary strongly with
the spacing between the two crystals. This is found to be a cooperative effect
due to two mechanisms: the chromatic dispersion of the medium separating the
crystals and spatiotemporal effects which arise from the inclusion of
transverse wave vectors. These effects provide two concomitant avenues for
controlling the quantum state generated in SPDC. We expect these results to be
of interest for the development of quantum technologies and the generation of
SPDC in periodically varying nonlinear materials.Comment: submitted to Physical Review
Intrinsic NLRP3 inflammasome activity is critical for normal adaptive immunity via regulation of IFN-Îł in CD4+ T cells
The NLRP3 inflammasome controls interleukin-1b maturation in antigen-presenting cells, but
a direct role for NLRP3 in human adaptive immune cells has not been described.We found that
the NLRP3 inflammasome assembles in human CD4+ Tcells and initiates caspase-1–dependent
interleukin-1b secretion, thereby promoting interferon-g production and T helper 1 (TH1)
differentiation in an autocrine fashion. NLRP3 assembly requires intracellular C5 activation and
stimulation of C5a receptor 1 (C5aR1), which is negatively regulated by surface-expressed
C5aR2. Aberrant NLRP3 activity in Tcells affects inflammatory responses in human
autoinflammatory disease and in mouse models of inflammation and infection. Our results
demonstrate that NLRP3 inflammasome activity is not confined to “innate immune cells” but is
an integral component of normal adaptive TH1 responses
Multi-tier Loyalty Programs to Stimulate Customer Engagement
Customers differ in their purchase behavior, profitability, attitude toward the firm, and so on. These differences between customers have led to numerous firms introducing multi-tier loyalty programs. A multi-tier loyalty program explicitly distinguishes between customers by means of hierarchical tiers (e.g. Silver, Gold, Platinum) and assigns customers to different tiers based on their past purchase behavior. Next, customers in different tiers are provided varying levels of tangible rewards and intangible benefits, which are potentially powerful instruments to stimulate customer engagement. In this chapter, we focus on the design and effectiveness of such multi-tier loyalty programs. Building on loyalty program and customer prioritization research, we discuss whether, why, and how multi-tier loyalty programs are effective (or not) in influencing customer behavior, thereby enhancing customer engagement and financial performance
The role of the complement system in traumatic brain injury: a review
Traumatic brain injury (TBI) is an important cause of disability and mortality in the western world. While the initial injury sustained results in damage, it is the subsequent secondary cascade that is thought to be the significant determinant of subsequent outcomes. The changes associated with the secondary injury do not become irreversible until some time after the start of the cascade. This may present a window of opportunity for therapeutic interventions aiming to improve outcomes subsequent to TBI. A prominent contributor to the secondary injury is a multifaceted inflammatory reaction. The complement system plays a notable role in this inflammatory reaction; however, it has often been overlooked in the context of TBI secondary injury. The complement system has homeostatic functions in the uninjured central nervous system (CNS), playing a part in neurodevelopment as well as having protective functions in the fully developed CNS, including protection from infection and inflammation. In the context of CNS injury, it can have a number of deleterious effects, evidence for which primarily comes not only from animal models but also, to a lesser extent, from human post-mortem studies. In stark contrast to this, complement may also promote neurogenesis and plasticity subsequent to CNS injury. This review aims to explore the role of the complement system in TBI secondary injury, by examining evidence from both clinical and animal studies. We examine whether specific complement activation pathways play more prominent roles in TBI than others. We also explore the potential role of complement in post-TBI neuroprotection and CNS repair/regeneration. Finally, we highlight the therapeutic potential of targeting the complement system in the context of TBI and point out certain areas on which future research is needed
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