Magnetic fields in cosmic particle acceleration sources

We review here some magnetic phenomena in astrophysical particle accelerators associated with collisionless shocks in supernova remnants, radio galaxies and clusters of galaxies. A specific feature is that the accelerated particles can play an important role in magnetic field evolution in the objects. We discuss a number of CR-driven, magnetic field amplification processes that are likely to operate when diffusive shock acceleration (DSA) becomes efficient and nonlinear. The turbulent magnetic fields produced by these processes determine the maximum energies of accelerated particles and result in specific features in the observed photon radiation of the sources. Equally important, magnetic field amplification by the CR currents and pressure anisotropies may affect the shocked gas temperatures and compression, both in the shock precursor and in the downstream flow, if the shock is an efficient CR accelerator. Strong fluctuations of the magnetic field on scales above the radiation formation length in the shock vicinity result in intermittent structures observable in synchrotron emission images. Resonant and non-resonant CR streaming instabilities in the shock precursor can generate mesoscale magnetic fields with scale-sizes comparable to supernova remnants and even superbubbles. This opens the possibility that magnetic fields in the earliest galaxies were produced by the first generation Population III supernova remnants and by clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review

Time-of-flight range detection using low-frequency intensity modulation of a cw laser diode: application to fiber length measurement

International audienceThis paper describes a simple optical range detector in the time-of-flight (TOF) category using a cw laser diode emitting at 1.55 µm. The principle of operation combines TOF with frequency-modulated cw methods. The main originality of this method consists in measuring the time delay between two signals without using the time variable. The forward current of the laser diode is modulated by a low-frequency triangular signal. The emitted and received signals are compared, and the amplitude difference gives a readout signal whose peak-to-peak amplitude is proportional to the TOF. An application to optical fiber lenth measurement is given

Novel holographic masking technique for Bragg reflector inscription on integrated optics components

A novel triangular interferometer configuration is used to inscribe periodic or aperiodic patterns with micronic or submicronic fringe spacing. It is employed to realize Bragg reflectors or resonant grating filters on integrated optical components

Bragg mirror inscription on LiNbO3 waveguides by index microstructuration

Numerous applications in integrated optics, especially those related to multiwavelength telecommunications, require dichroic reflectors for use as narrowband or broadband wavelength-selective filters. Bragg mirrors are excellent candidates for this purpose, and we describe a method of fabricating Bragg grating reflectors in Ti-indiffused Lithium Niobate single-mode waveguides based on holographic masking in association with proton exchange. The holographic setup is employed to record a photolithographic mask directly on the substrate, enabling the inscription of waveguides with both periodic and aperiodic distributed parameters

First demonstration of parabolic pulse generation in comb-like profiled dispersion decreasing fiber

International audienc

Experimental demonstration of parabolic similariton generation in comb-like dispersion-decreasing fiber

International audienc

All-Fiber Source of 20 fs Pulses at 1550 nm using Two Stage Linear-Nonlinear Compression of Parabolic Similaritons

International audienceParabolic pulses from a similariton amplifier at 1550nm are compressed using a two-stage fiber compressor employing linear compression in photonic bandgap fiber and soliton effect compression in highly nonlinear fiber. Precise optimization of the compressor design using frequency resolved optical gating allows the generation of minimally chirped pulses as short as 20fs. This duration corresponds to only four optical cycles of the underlying electric field at this wavelengt

Mesure par conductimetrie de la receptivite aux maladies fongiques et du niveau de resistance induite par elicitation. Etude sur 3 modeles experimentaux

L’appréciation des dégâts parasitaires, souvent difficile à évaluer, peut être effectuée par des mesures conductimétriques; en effet, les cellules altérées libèrent davantage d’électrolytes que les cellules saines dans le milieu extérieur, dont on mesure la conductance. Cette méthode peut être utilisée dans différents cas, notamment lorsqu’il y a attaque au niveau racinaire. On mesure alors la conductance de l’eau dans laquelle baignent des racines contaminées (piment - Phytophthora capsici, tableau I), ou des feuilles appartenant à des plantes dont le système racinaire est malade (blé - Gaeumannomyces graminis) (tableau II). Les mesures de perte d’électrolytes par conductimétrie apportent également des renseignements intéressants sur la réceptivité aux maladies des tissus sains; celle-ci varie en particulier avec l’âge des tissus, notamment en fonction de la hauteur des entre-nœuds et des étages foliaires; elle peut être mesurée par la quantité d’ions relargués, car une bonne corrélation existe entre les notes de sensibilité à la maladie et la conductance des tissus sains. Les études ont été conduites, d’une part, sur le couple maïs - Helminthosporium turcicum (tableau III avec r = + 0,953) et d’autre part, sur le couple piment - Phytophthora capsici (tableau IV avec r = + 0,909 pour les feuilles et r = + 0,932 pour les tiges). Les éliciteurs ont la propriété d’induire chez les végétaux des mécanismes de défense. Le passage à l’état élicité se traduit par une modification de la perméabilité cellulaire qui a pu être observée ici avec 2 éliciteurs phospholipidiques : un sphingophospholipide à inositol issu de P capsici et une phosphatidylcholine issue de G graminis. L’étude sur piment, qu’il s’agisse d’élicitation directe ou d’élicitation à distance (tableau V), montre que les tissus traités relarguent de moins en moins d’électrolytes au fur et à mesure que la concentration en éliciteur augmente et que la protection se renforce. Il existe cependant une concentration en éliciteur optimale au-delà de laquelle l’effet s’inverse. Chez le blé, les semences ayant germé en présence d’éliciteur donnent des plantules qui libèrent moins d’électrolytes que les témoins (tableau VI). L’intérêt de cette méthode en phytopathologie est discuté.Damage to plants due to parasites is often difficult to evaluate, particularly in root system diseases. When altered cells (necrotic or with altered metabolism) are soaked in water, they leak electrolytes and the conductance of the surrounding solution increases. For example, the amount of electrolytes released by pepper roots attacked by Phytophthora capsici increases with zoospore concentration (table I); likewise, at flowering time, leaves of wheat (when floated on water) contaminated by Gaeumannomyces graminis have a higher conductance than the healthy control (table II). The susceptibility of healthy tissues changes with age, particularly with the height of internodes and foliar position above the soil. In the corn - Helminthosporium turcicum (table III) and pepper - P capsici system interactions (table IV), there is a good correlation between the conductance of healthy tissues and the susceptibility ratings of corresponding tissues (corn leaf, r = 0.953; pepper leaf, r = 0.909; pepper stem, r = 0.932). Elicitation may be performed either by soaking detached cotyledons or by truncating and soaking non-detached cotyledons (pepper, table V) or by soaking the seeds (wheat, table VI). Two phospholipid elicitors are used: inositol sphingophospholipid isolated from P capsici and phosphatidylcholine isolated from G graminis. The elicitor amount of electrolytes leaked by plants decreases whith increasing concentrations. However, there is an optimum concentration (between 5 and 10 μg/ml) beyond which the effect is reversed

Generation of ultrafast Bessel micro-beams and applications to laser surface nanoprocessing

International audienceThe novel propagation characteristics of Bessel beams have been widely applied to optical manipulation and harmonic generation, and have provided new perspectives on fundamentals of ultrashort laser pulse propagation in nonlinear media. Fully exploiting their many unique properties, however, requires the development of techniques for the generation of high quality Bessel beams with flexible adjustment of the beam parameters. Moreover, long working distances are needed to produce Bessel beams inside bulk samples. In this paper, we report on the development of a novel spatial light modulator based setup that combines the properties of parameter flexibility, long working distance, high throughput and operation on micron-scale. We report both on the general characterization of the beam properties as well as a specific application in surface nanoprocessing

Optimized one-step compression of femtosecond fibre laser pulses to 30 fs in dispersion-flattened highly nonlinear fibre

In this paper, however, we show that it is possible to obtain high quality nonlinear compressed pulses using only one segment of readily-available highly nonlinear fiber (HNLF). By directly splicing a very short (7 cm) length of HNLF to the output single mode fiber pigtail of a commercial femtosecond fiber laser, frequency resolved optical gating (FROG) confirms that nonlinear compression results in the generation of 28 fs pulses. This represents an extremely simple modification allowing an essentially loss-free factor-of-three reduction in pulse duration relative to the primary source