207 research outputs found
All-Dielectric Rod-Type Metamaterials at Optical Frequencies
Light propagation in all-dielectric rod-type metamaterials is studied
theoretically. The electric and magnetic dipole moments of the rods are derived
analytically in the long-wavelength limit. The effective permittivity and
permeability of a square lattice of rods are calculated by homogenizing the
corresponding array of dipoles. The role of dipole resonances in the optical
properties of the rod array is interpreted. This structure is found to exhibit
a true left-handed behavior, confirming previous experiments [L. Peng
\textit{et al.}, Phys. Rev. Lett. \textbf{98}, 157403 (2007)]. A scaling
analysis shows that this effect holds at optical frequencies and can be
obtained by using rods made, for example, of silicon.Comment: 10 pages, 4 figures. The title has been shortened; Figs. 1, 2 and 3
have been modified; Eq. 4 has been corrected (sign error); A few sentences
have been added/rewritte
Efficient light coupling into a photonic crystal waveguide with flatband slow mode
We design an efficient coupler to transmit light from a strip waveguide into
the flatband slow mode of a photonic crystal waveguide with ring-shaped holes.
The coupler is a section of a photonic crystal waveguide with a higher group
velocity, obtained by different ring dimensions. We demonstrate coupling
efficiency in excess of 95% over the 8 nm wavelength range where the photonic
crystal waveguide exhibits a quasi constant group velocity vg = c/37. An
analysis based on the small Fabry-P\'erot resonances in the simulated
transmission spectra is introduced and used for studying the effect of the
coupler length and for evaluating the coupling efficiency in different parts of
the coupler. The mode conversion efficiency within the coupler is more than
99.7% over the wavelength range of interest. The parasitic reflectance in the
coupler, which depends on the propagation constant mismatch between the slow
mode and the coupler mode, is lower than 0.6% within this wavelength range.Comment: 11 pages, 7 figures, submitted to Photonics and Nanostructures -
Fundamentals and Application
The effect of discharge chamber geometry on the ignition of low-pressure rf capacitive discharges
This paper reports measured and calculated breakdown curves in several gases of rf capacitive discharges excited at 13.56 MHz in chambers of three different geometries: parallel plates surrounded by a dielectric cylinder (“symmetric parallel plate”), parallel plates surrounded by a
grounded metallic cylinder (“asymmetric parallel plate”), and parallel plates inside a much larger grounded metallic chamber (“large chamber”). The breakdown curves for the symmetric chamber have a multivalued section at low pressure. For the asymmetric chamber the breakdown curves are shifted to lower pressures and rf voltages, but the multivalued feature is still present. At higher pressures the breakdown voltages are much lower than for the symmetric geometry. For the large chamber geometry the multivalued behavior is not observed. The breakdown curves were also calculated using a numerical model based on fluid equations, giving results that are in satisfactory
agreement with the measurements
Modes and the alpha-gamma transition in rf capacitive discharges in N2O at different rf frequencies
This paper reports current-voltage characteristics and pressure-voltage transition curves from the weak-current a-mode to the strong-current g-mode for rf capacitive discharges in N2O at
frequencies of 2 MHz, 13.56 MHz, and 27.12 MHz. At 2 MHz the rf discharge is mostly resistive whereas at 13.56 MHz and 27.12 MHz it is mostly capacitive. The weak-current a-mode was found to exist only above a certain minimum gas pressure for all frequencies studied [N. Yatsenko Sov. Phys. Tech. Phys. 26, 678 (19810] previously proposed that the a−g transition corresponds to
breakdown of the sheaths. However, we show that this is the case only for sufficiently high gas pressures. At lower pressure there is a smooth transition from the weak-current a-mode to a strong-current g-mode, in which the sheaths produce fast electrons but the sheath has not undergone breakdown
A 2022 -Herculid meteor cluster from an airborne experiment: automated detection, characterization, and consequences for meteoroids
Context. The existence of meteor clusters has long since been a subject of
speculation and so far only seven events have been reported, among which two
involve less than five meteors, and three were seen during the Leonid storms.
Aims. The 1995 outburst of Comet 73P/Schwassmann-Wachmann was predicted to
result in a meteor shower in May 2022. We detected the shower, proved this to
be the result of this outburst, and detected another meteor cluster during the
same observation mission. Methods. The {\tau}-Herculids meteor shower outburst
on 31 May 2022 was continuously monitored for 4 hours during an airborne
campaign. The video data were analyzed using a recently developed
computer-vision processing chain for meteor real-time detection. Results. We
report and characterize the detection of a meteor cluster involving 38
fragments, detected at 06:48 UT for a total duration of 11.3 s. The derived
cumulative size frequency distribution index is relatively shallow: s = 3.1.
Our open-source computer-vision processing chain (named FMDT) detects 100% of
the meteors that a human eye is able to detect in the video. Classical
automated motion detection assuming a static camera was not suitable for the
stabilized camera setup because of residual motion. Conclusions. From all
reported meteor clusters, we crudely estimate their occurrence to be less than
one per million observed meteors. Low heliocentric distance enhances the
probability of such meteoroid self-disruption in the interplanetary space.Comment: 6 pqges, 5 figure
Nonlinear optical characterization of functionalized organometallic complexes using THG and Z-scan techniques
We report the measurements of third-order nonlinear optical (NLO) properties in picosecond regim of functionalized organometallic complexes using third harmonic generation (THG) and Z-scan techniques. We show the results obtained for solutions dissolved in dichloromethane with different concentrations. For each chromophore, we give the values of: the nonlinear absorption coefficient β, the nonlinear refractive index n2, the third-order nonlinear susceptibility χ 3 and the second-order nonlinear hyperpolarisability γ of individual molecules. This approach allowed us to determine also the electronic and rotational contributions of χ 3 by using a picosecond laser Nd:YAG at the fundamental wavelength 1064 nm
Actes de la 9ème conférence des Technologies de l’Information et de la Communication pour l’Enseignement (TICE 2014)
National audienceLe cycle de conférence TICE a pour objectif de faire tous les deux ans le point sur les résultats de recherches, les nouvelles applications, les derniers usages, et les retours d’expériences dans le domaine de l’éducation supérieure numérique. Le colloque TICE 2014 est organisé par l’IUT de Beziers, une composante de l’Université Montpellier 2. Cette neuvième édition du colloque TICE sera l’occasion de rassembler à Béziers, du 18 au 20 Novembre 2014, la communauté scientifique et industrielle des TICE autour du thème « Nouvelles pédagogies et sciences et technologies du numérique »
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