1,067 research outputs found
On the statistical interpretation of optical rogue waves
Numerical simulations are used to discuss various aspects of "optical rogue
wave" statistics observed in noise-driven fiber supercontinuum generation
associated with highly incoherent spectra. In particular, we consider how long
wavelength spectral filtering influences the characteristics of the statistical
distribution of peak power, and we contrast the statistics of the spectrally
filtered SC with the statistics of both the peak power of the most red-shifted
soliton in the SC and the maximum peak power across the full temporal field
with no spectral selection. For the latter case, we show that the unfiltered
statistical distribution can still exhibit a long-tail, but the extreme-events
in this case correspond to collisions between solitons of different
frequencies. These results confirm the importance of collision dynamics in
supercontinuum generation. We also show that the collision-induced events
satisfy an extended hydrodynamic definition of "rogue wave" characteristics.Comment: Paper accepted for publication in the European Physical Journal ST,
Special Topics. Discussion and Debate: Rogue Waves - towards a unifying
concept? To appear 201
Simultaneous fs pulse spectral broadening and third harmonic generation in highly nonlinear fibre: experiments and simulations
Experiments and numerical simulations are used to study non-phasematched single-mode third harmonic generation occurring simultaneously with fs pulse spectral broadening in highly nonlinear fibre. Pump pulses around 100 fs at 1560 nm injected into sub-5 cm lengths of commercially-available highly nonlinear fibre are observed to undergo spectral broadening spanning over 700 nm at the -30 dB level, and to simultaneously generate third harmonic radiation around 520 nm. Simulations based on a generalized nonlinear envelope equation are shown to well reproduce the spectral structure of the broadened pump pulses and the generated third harmonic signal
Evolution in prostheses for sprinters with lower-limb amputation
Depuis une quinzaine d'annĂ©es, les progrĂšs techniques en appareillage ont Ă©tĂ© le facteur dĂ©terminant de la progression des performances des sportifs amputĂ©s de membre infĂ©rieur. Pour l'amputĂ© tibial, la prothĂšse de course comprend un manchon gel et une emboĂźture solidarisĂ©s par un accrochage distal ou un vide virtuel. Par ses qualitĂ©s dynamiques, le pied en fibre de carbone, garni de pointes, assure des performances remarquables. Pour l'amputĂ© fĂ©moral, Ă©quipĂ© des mĂȘmes pieds prothĂ©tiques, le genou est Ă biellettes et Ă contrĂŽle des phases d'appui et pendulaire. Par rapport au coureur valide, le temps d'appui sur le membre appareillĂ© est raccourci tandis que celui sur le membre sain est allongĂ©. L'asymĂ©trie du sprint de l'amputĂ© tibial est discrĂšte. C'est le travail des extenseurs de hanche qui est la principale compensation au dĂ©ficit de propulsion dĂ» Ă l'amputation. Chez l'amputĂ© fĂ©moral, l'absence de genou aggrave l'asymĂ©trie. L'extension totale du genou prothĂ©tique, prĂ©coce en fin de phase oscillante et persistant pendant toute la phase d'appui, impose une compensation par une augmentation d'extension de la hanche controlatĂ©rale. Les transferts de charge de travail entre cĂŽtĂ© amputĂ© et sain, par l'intermĂ©diaire d'une hyperlordose lombaire, mettent en jeu le bassin, le tronc et les Ă©paules. Les amputĂ©s sportifs font progresser la recherche en appareillage. Leurs orthoprothĂ©sistes acquiĂšrent avec eux un savoir-faire dont bĂ©nĂ©ficient leurs patients non-sportifs.For about 15 years, technical advances in prosthetic treatment have been the main factor in the increased performance of athletes with lower-limb amputation. For trans-tibial amputation, the prosthesis for sprinting is composed of a gel liner and a socket joined by a locking or virtual vacuum liner. Because of these dynamic properties, the carbon prosthetic foot equipped with tacks ensures outstanding performance. For trans-femoral amputation, a hydraulic swing and a stance control unit are added to the same prosthesis. In comparison with the able-bodied runner, athletes with amputation have smaller loading times in the prosthetic limb and larger ones in the sound limb. The length of the energy-storing prosthetic foot is determined by the âup-on-the-toesâ running gait. The sprinting gait with trans-tibial amputation is almost symmetrical. The hip extensor effort is the main compensation of propulsion reduction with lower-limb amputation. With trans-femoral amputation, the lack of knee increases the asymmetry. The total prosthetic knee extension (early in late-swing phase and lasting during total stance phase) compensates with extension of both hips, especially the opposite one. The amputation and sound limb load transfer with lumbar hyperlordosis concern the pelvis, trunk and shoulders. Because of athletes with amputation, research in prosthetic treatment has progressed. The development of orthotics and prostheses for such athletes has benefited non-athletes with amputation
Influence of Al-doped ZnO Transparent Contacts Deposited by a Spray Pyrolysis Technique on Performance of HIT Solar Cells
AbstractTransparent and conductive Al-doped ZnO (AZO) thin films were deposited by spray pyrolysis and analysed in the aim to improve optical and electrical properties involved in the efficiency of Heterostructure with Intrinsic Thin Layer (HIT) solar cell. X-ray diffraction measurement shows that AZO film grown on glass has (002) preferred orientation. High optical transmittance value of âŒ80% in the visible region was observed and the optical band gap was found to be 3.31eV at room temperature. The influence of AZO thin films as transparent conductive oxide TCO on heterojunction with intrinsic thin-layer (HIT) solar cell performance was investigated using software simulation. The beneficial effect of implementing AZO front contact for increasing electrical energy conversion properties of HIT solar cell compared to the reference cell without the AZO layer
Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation
Numerical simulations of the onset phase of continuous wave supercontinuum
generation from modulation instability show that the structure of the field as
it develops can be interpreted in terms of the properties of Akhmediev
Breathers. Numerical and analytical results are compared with experimental
measurements of spectral broadening in photonic crystal fiber using nanosecond
pulsesComment: 22 pages, 6 figure
Theory of radiation trapping by the accelerating solitons in optical fibers
We present a theory describing trapping of the normally dispersive radiation
by the Raman solitons in optical fibers. Frequency of the radiation component
is continuously blue shifting, while the soliton is red shifting. Underlying
physics of the trapping effect is in the existence of the inertial gravity-like
force acting on light in the accelerating frame of reference. We present
analytical calculations of the rate of the opposing frequency shifts of the
soliton and trapped radiation and find it to be greater than the rate of the
red shift of the bare Raman soliton. Our findings are essential for
understanding of the continuous shift of the high frequency edge of the
supercontinuum spectra generated in photonic crystal fibers towards higher
frequencies.Comment: Several misprints in text and formulas corrected. 10 pages, 9
figures, submitted to Phys. Rev.
Real time noise and wavelength correlations in octave-spanning supercontinuum generation
We use dispersive Fourier transformation to measure shot-to-shot spectral
instabilities in femtosecond supercontinuum generation. We study both the onset
phase of supercontinuum generation with distinct dispersive wave generation, as
well as a highly-unstable supercontinuum regime spanning an octave in
bandwidth. Wavelength correlation maps allow interactions between separated
spectral components to be identified, even when such interactions are not
apparent in shot-to-shot or average measurements. Experimental results are
interpreted using numerical simulations. Our results show the clear advantages
of dispersive Fourier transformation for studying spectral noise during
supercontinuum generation.Comment: 14 pages, 5 figure
Real-time full bandwidth measurement of spectral noise in supercontinuum generation
The ability to measure real-time fluctuations of ultrashort pulses
propagating in optical fiber has provided significant insights into fundamental
dynamical effects such as modulation instability and the formation of
frequency-shifting rogue wave solitons. We report here a detailed study of
real-time fluctuations across the full bandwidth of a fiber supercontinuum
which directly reveals the significant variation in measured noise statistics
across the spectrum, and which allows us to study correlations between widely
separated spectral components. For two different propagation distances
corresponding to the onset phase of spectral broadening and the fully-developed
supercontinuum, we measure real time noise across the supercontinuum bandwidth,
and we quantify the supercontinuum noise using statistical higher-order moments
and a frequency-dependent intensity correlation map. We identify correlated
spectral regions within the supercontinuum associated with simultaneous
sideband generation, as well as signatures of pump depletion and soliton-like
pump dynamics. Experimental results are in excellent agreement with
simulations
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