875 research outputs found
Parabolic pulse generation with active or passive dispersion decreasing optical fibers
We experimentally demonstrate the possibility to generate
parabolic pulses via a single dispersion decreasing optical fiber with normal
dispersion. We numerically and experimentally investigate the influence of
the dispersion profile, and we show that a hybrid configuration combining
dispersion decrease and gain has several benefits on the parabolic generated
pulses
Far infrared absorption by acoustic phonons in titanium dioxide nanopowders
We report spectral features of far infrared electromagnetic radiation
absorption in anatase TiO2 nanopowders which we attribute to absorption by
acoustic phonon modes of nanoparticles. The frequency of peak excess absorption
above the background level corresponds to the predicted frequency of the
dipolar acoustic phonon from continuum elastic theory. The intensity of the
absorption cannot be accounted for in a continuum elastic dielectric
description of the nanoparticle material. Quantum mechanical scale dependent
effects must be considered. The absorption cross section is estimated from a
simple mechanical phenomenological model. The results are in plausible
agreement with the absorption being due to a sparse layer of charge on the
nanoparticle surface.Comment: 8 pages, 5 figures, submitted to Journal of Nanoelectronics and
Optoelectronic
Observation of a Group of Dark Rogue Waves in a Telecommunication Optical Fiber
Over the past decade, the rogue wave debate has stimulated the comparison of
predictions and observations among different branches of wave physics,
particularly between hydrodynamics and optics, in situations where analogous
dynamical behaviors can be identified, thanks to the use of common universal
models. Although the scalar nonlinear Schroedinger equation (NLSE) has
constantly played a central role for rogue wave investigations, moving beyond
the standard NLSE model is relevant and needful for describing more general
classes of physical systems and applications. In this direction, the coupled
NLSEs are known to play a pivotal role for the understanding of the complex
wave dynamics in hydrodynamics and optics. Benefiting from the advanced
technology of high-speed telecommunication-grade components, and relying on a
careful design of the nonlinear propagation of orthogonally-polarized optical
pump waves in a randomly birefringent telecom fiber, this work explores, both
theoretically and experimentally, the rogue wave dynamics governed by such
coupled NLSEs. We report, for the first time, the evidence of a group of three
dark rogue waves, the so-called dark three-sister rogue waves, where
experiments, numerics, and analytics show a very good consistency
High-Resolution Nonlinear Raman Spectroscopy in Gases
The applicability of Raman spectroscopy to the investigation
of gases has been greatly improved by the development of the
different methods of nonlinear Raman scattering. When two laser
beams, one of which has a tunable frequency, are brought to a
common focus in a sample, a stimulated Raman process occurs, as
soon as the frequency difference between the two lasers is equal
to aRaman active rovibrational or rotational transition frequency
of the sarnple, and the corresponding state is popuJated above
equilibrium. The Raman resonance can be detected in different
ways: by coherent anti-Stokes Raman scattering (CARS) or the
corresponding Stokes process (CSRS), by again in one of the
beams (stimulated Raman gain spectroscopy, SRGS) or a loss in
the other one (inverse Raman spectroscopy, IRS), or even by detection of a photoacoustic signal (photoacoustic Raman spectroscopy,PARS). The selective ionisation of the excited molecules by a third ultraviolet laser pulse (ionisation detected stimulated Raman scattering, IDSRS) has considerably increased the sensitivity in special cases. The instrumental resolution of the se techniques is determined by the convoluted linewidths of the lasers used for excitation. This is of special importance for the investigation of high resolution rotation-vibrational spectra of gases
Inelastic neutron scattering due to acoustic vibrations confined in nanoparticles: theory and experiment
The inelastic scattering of neutrons by nanoparticles due to acoustic
vibrational modes (energy below 10 meV) confined in nanoparticles is calculated
using the Zemach-Glauber formalism. Such vibrational modes are commonly
observed by light scattering techniques (Brillouin or low-frequency Raman
scattering). We also report high resolution inelastic neutron scattering
measurements for anatase TiO2 nanoparticles in a loose powder. Factors enabling
the observation of such vibrations are discussed. These include a narrow
nanoparticle size distribution which minimizes inhomogeneous broadening of the
spectrum and the presence of hydrogen atoms oscillating with the nanoparticle
surfaces which enhances the number of scattered neutrons.Comment: 3 figures, 1 tabl
Polarization modulation instability in a Manakov fiber system
The Manakov model is the simplest multicomponent model of nonlinear wave theory: It describes elementary
stable soliton propagation and multisoliton solutions, and it applies to nonlinear optics, hydrodynamics, and
Bose-Einstein condensates. It is also of fundamental interest as an asymptotic model in the context of the
widely used wavelength-division-multiplexed optical fiber transmission systems. However, although its physical
relevance was confirmed by the experimental observation of Manakov (vector) solitons in a planar waveguide in
1996, there have in fact been no quantitative experiments confirming its validity for nonlinear dynamics other than
soliton formation. Here, we report experiments in optical fiber that provide evidence of passband and baseband
polarization modulation instabilities in a defocusing Manakov system. In the spontaneous regime, we also reveal
a unique saturation effect as the pump power increases. We anticipate that such observations may impact the
application of this minimal model to describe and understand more complicated phenomena in nature, such as
the formation of extreme waves in multicomponent systems
Spatiotemporal Characterization of Supercontinuum Extending from the Visible to the Mid-Infrared in Multimode Graded-Index Optical Fiber
We experimentally demonstrate that pumping a graded-index multimode fiber
with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat
supercontinuum generation with a uniform bell-shaped spatial beam profile
extending from the visible to the mid-infrared at 2500\,nm. We study the
development of the supercontinuum along the multimode fiber by the cut-back
method, which permits us to analyze the competition between the Kerr-induced
geometric parametric instability and stimulated Raman scattering. We also
performed a spectrally resolved temporal analysis of the supercontinuum
emission.Comment: 5 pages 7 figure
Elucidating the crystal-chemistry of Jbel Rhassoul stevensite (Morocco) by advanced analytical techniques
The composition of Rhassoul clay is controversial regarding the nature of the puremineral clay fraction which is claimed to be stevensite rather than saponite. In this study, the raw and mineral fractions were characterized using various techniques including Fourier transform infrared spectroscopy and magic angle spinning nuclear magnetic resonance (MAS NMR). The isolated fine clay mineral fraction contained a larger amount of Al (>1 wt.%) than that reported for other stevensite occurrences. The 27Al MAS NMR technique confirmed that the mineral is stevensite in which the Al is equally split between the tetrahedral and octahedral coordination sites. The 29Si NMR spectrum showed a single unresolved resonance indicating little or no short-range ordering of silicon. The chemical composition of the stevensite from Jbel Rhassoul was determined to be ((Na0.25K0.20 (Mg5.04Al0.37Fe0.20&0.21)5.61(Si7.76Al0.24)8O20(OH)4). This formula differs from previous compositions described from this locality and shows it to be an Al-bearing lacustrine clay mineral
- …