956 research outputs found
Mid-infrared sub-wavelength grating mirror design: tolerance and influence of technological constraints
High polarization selective Si/SiO2 mid-infrared sub-wavelength grating
mirrors with large bandwidth adapted to VCSEL integration are compared. These
mirrors have been automatically designed for operation at \lambda = 2.3 m
by an optimization algorithm which maximizes a specially defined quality
factor. Several technological constraints in relation with the grating
manufacturing process have been imposed within the optimization algorithm and
their impact on the optical properties of the mirror have been evaluated.
Furthermore, through the tolerance computation of the different dimensions of
the structure, the robustness with respect to fabrication errors has been
tested. Finally, it appears that the increase of the optical performances of
the mirror imposes a less tolerant design with severer technological
constraints resulting in a more stringent control of the manufacturing process.Comment: The final publication is available at
http://iopscience.iop.org/2040-8986/13/12/125502
MĂ©decine physique et de rĂ©adaptation et cancer : Ă©tat de lâart et analyse de la littĂ©rature
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
Great ape gestures : intentional communication with a rich set of innate signals
Great apes give gestures deliberately and voluntarily, in order to influence particular target audiences, whose direction of attention they take into account when choosing which type of gesture to use. These facts make the study of ape gesture directly relevant to understanding the evolutionary precursors of human language; here we present an assessment of ape gesture from that perspective, focusing on the work of the âSt Andrews Groupâ of researchers. Intended meanings of ape gestures are relatively few and simple. As with human words, ape gestures often have several distinct meanings, which are effectively disambiguated by behavioural context. Compared to the signalling of most other animals, great ape gestural repertoires are large. Because of this, and the relatively small number of intended meanings they achieve, ape gestures are redundant, with extensive overlaps in meaning. The great majority of gestures are innate, in the sense that the speciesâ biological inheritance includes the potential to develop each gestural form and use it for a specific range of purposes. Moreover, the phylogenetic origin of many gestures is relatively old, since gestures are extensively shared between different genera in the great ape family. Acquisition of an adult repertoire is a process of first exploring the innate species potential for many gestures and then gradual restriction to a final (active) repertoire that is much smaller. No evidence of syntactic structure has yet been detected.Publisher PDFPeer reviewe
Real-time measurements of dissipative solitons in a mode-locked fiber laser
Dissipative solitons are remarkable localized states of a physical system
that arise from the dynamical balance between nonlinearity, dispersion and
environmental energy exchange. They are the most universal form of soliton that
can exist in nature, and are seen in far-from-equilibrium systems in many
fields including chemistry, biology, and physics. There has been particular
interest in studying their properties in mode-locked lasers producing
ultrashort light pulses, but experiments have been limited by the lack of
convenient measurement techniques able to track the soliton evolution in
real-time. Here, we use dispersive Fourier transform and time lens measurements
to simultaneously measure real-time spectral and temporal evolution of
dissipative solitons in a fiber laser as the turn-on dynamics pass through a
transient unstable regime with complex break-up and collision dynamics before
stabilizing to a regular mode-locked pulse train. Our measurements enable
reconstruction of the soliton amplitude and phase and calculation of the
corresponding complex-valued eigenvalue spectrum to provide further physical
insight. These findings are significant in showing how real-time measurements
can provide new perspectives into the ultrafast transient dynamics of complex
systems.Comment: See also M. Narhi, P. Ryczkowski, C. Billet, G. Genty, J. M. Dudley,
Ultrafast Simultaneous Real Time Spectral and Temporal Measurements of Fibre
Laser Modelocking Dynamics, 2017 Conference on Lasers and Electro-Optics
Europe & European Quantum Electronics Conference, paper EE-3.5 (2017
Robust design of Si/Si3N4 high contrast grating mirror for mid-infrared VCSEL application
A Si/Si3N4 high contrast grating mirror has been designed for a VCSEL
integration in mid-infrared ({\lambda} = 2.65 m). The use of an
optimization algorithm which maximizes a VCSEL mirror quality factor allowed
the adjustment of the grating parameters while keeping large and shallow
grating pattern. The robustness with respect to fabrication error has been
enhanced thanks to a precise study of the grating dimension tolerances. The
final mirror exhibits large high reflectivity bandwidth with a polarization
selectivity and several percent of tolerance on the grating dimensions.Comment: The final publication is available at http://www.springerlink.com,
Optical and Quantum Electronics (2012) Online Firs
Transitions dipolaires induites par collisions sur un faisceau de formaldéhyde. Effet d'un champ électrique
Using a H2CO molecular beam, a method is first described which permits the observation of rotational transitions ÎJ = ± n (n ✠1), induced by collisions with the molecules of a target gas. In the case H2CO â H 2CO, selection rules are defined and rotational resonance effects are observed on the differential cross sections for some ÎJ = â 1 transitions. It appears that a direct electric field E considerably modifies the H2CO cross sections ÏJ. Using the pair H 2CO â NH3, the study of ÏJ variations with E shows that the ÎJ = 0 transitions become forbidden, when E is intense. The experimental results are compared with the theoretical transition probabilities variations, due to E and calculated in the Born approximation. An experimental method is deduced which permits, by application of an electric field, to select AJ = 0 transitions on a molecular beam.Nous prĂ©sentons d'abord une mĂ©thode expĂ©rimentale qui permet d'observer les transitions rotationnelles ÎJ = ± n (n ✠1) induites par collisions entre les molĂ©cules d'un faisceau de formaldĂ©hyde et un gaz tampon. En prenant H2CO comme gaz tampon, nous prĂ©cisons les rĂšgles de sĂ©lection et, sur les sections de collisions correspondant Ă plusieurs transitions ÎJ = â 1, nous mettons en Ă©vidence des effets de rĂ©sonance rotationnelle. Nous constatons qu'un champ Ă©lectrique continu modifie considĂ©rablement les sections de collisions du formaldĂ©hyde. Sur le systĂšme dipolaire H2 CO-NH3, l'Ă©tude des variations caractĂ©ristiques de celles-ci en fonction du champ appliquĂ© montre que les transitions ÎJ. = 0 de H2CO deviennent interdites en champ fort. Nous comparons les rĂ©sultats expĂ©rimentaux aux variations de probabilitĂ© de transition dues au champ Ă©lectrique et calculĂ©es dans l'approximation de Born. On dĂ©duit une mĂ©thode expĂ©rimentale permettant de trier par effet de champ les transitions ÎJ = 0 sur le faisceau molĂ©culaire
Ăvaluation de la fonction des membres prĂ©sentant un lymphĆdĂšme par un nouveau test aprĂšs rĂ©Ă©ducation intensive
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