Filamentational Instability of Partially Coherent Femtosecond Optical Pulses in Air

The filamentational instability of spatially broadband femtosecond optical pulses in air is investigated by means of a kinetic wave equation for spatially incoherent photons. An explicit expression for the spatial amplification rate is derived and analyzed. It is found that the spatial spectral broadening of the pulse can lead to stabilization of the filamentation instability. Thus, optical smoothing techniques could optimize current applications of ultra-short laser pulses, such as atmospheric remote sensing.Comment: 8 pages, 2 figures, to appear in Optics Letter

RYDE: A Digital Signature Scheme based on Rank-Syndrome-Decoding Problem with MPCitH Paradigm

We present a signature scheme based on the Syndrome-Decoding problem in rank metric. It is a construction from multi-party computation (MPC), using a MPC protocol which is a slight improvement of the linearized-polynomial protocol used in [Fen22], allowing to obtain a zero-knowledge proof thanks to the MPCitH paradigm. We design two different zero-knowledge proofs exploiting this paradigm: the first, which reaches the lower communication costs, relies on additive secret sharings and uses the hypercube technique [AMGH+22]; and the second relies on low-threshold linear secret sharings as proposed in [FR22]. These proofs of knowledge are transformed into signature schemes thanks to the Fiat-Shamir heuristic [FS86].Comment: arXiv admin note: substantial text overlap with arXiv:2307.0857

The Blockwise Rank Syndrome Learning problem and its applications to cryptography

Recently the notion of blockwise error in a context of rank based cryptography has been introduced by Sont et al. at AsiaCrypt 2023 . This notion of error, very close to the notion sum-rank metric, permits, by decreasing the weight of the decoded error, to greatly improve parameters for the LRPC and RQC cryptographic schemes. A little before the multi-syndromes approach introduced for LRPC and RQC schemes had also allowed to considerably decrease parameters sizes for LRPC and RQC schemes, through in particular the introduction of Augmented Gabidulin codes. In the present paper we show that the two previous approaches (blockwise errors and multi-syndromes) can be combined in a unique approach which leads to very efficient generalized RQC and LRPC schemes. In order to do so, we introduce a new problem, the Blockwise Rank Support Learning problem, which consists of guessing the support of the errors when several syndromes are given in input, with blockwise structured errors. The new schemes we introduce have very interesting features since for 128 bits security they permit to obtain generalized schemes for which the sum of public key and ciphertext is only 1.4 kB for the generalized RQC scheme and 1.7 kB for the generalized LRPC scheme. The new approach proposed in this paper permits to reach a 40 % gain in terms of parameters size when compared to previous results, obtaining even better results in terms of size than for the KYBER scheme whose total sum is 1.5 kB. Besides the description of theses new schemes the paper provides new attacks for the l-RD problem introduced in the paper by Song et al. of AsiaCrypt 2023, in particular these new attacks permit to cryptanalyze all blockwise LRPC parameters they proposed (with an improvement of more than 40bits in the case of structural attacks). We also describe combinatorial attacks and algebraic attacks, for the new Blockwise Rank Support Learning problem we introduce

Les enclos du haut Moyen Âge de Vauvert à Château-Gontier (Mayenne)

Le site de Vauvert, repéré d’avion par G.Leroux en 1992, se compose de fossés pour la plupart profondément creusés dans les schistes précambriens. Ils limitent plusieurs parcelles carrées ou rectangulaires. La plus ancienne, établie à la fin du viesiècle ou au siècle suivant constitue sans doute le noyau initial du site. Plusieurs parcelles vont venir progressivement entourer cet enclos primitif dont nous n’avons pu fouiller qu’une petite partie, le reste ayant été détruit juste avant l’évaluation de J.-C.Meuret en 1999. Les structures d’habitat découvertes sont rares et souvent mal conservées. Elles se résument à un four domestique, une fosse complexe, quelques trous de poteau, des fosses-tranchées énigmatiques et une sépulture établie dans le fond d’un fossé. La partie explorée de ce site, qui appartient à la périphérie d’un habitat beaucoup plus vaste, n’est plus occupée après la période carolingienne.The Vauvert site, identified from the air by G. Leroux in 1992, consists of ditches most deeply cut in precambrian schists, which delimit several square rectangular plots. The earliest, established by the end of Vth century AD or during the following one, is probably the initial nucleus of the site. Several others progressively surround this basic enclosure; we could only excavate a small part, the rest having been destroyed just before evaluation by J.-C. Meuret in 1999. The domestic structures are few and often ill-preserved: a domestic hearth, a complex pit, some postholes, some engmatic ditches and a grave placed in the bottom of a ditch. The explored part of the site, which belongs to the periphery of a much larger settlement, is no longer occupied after the Carolingian period

On negative higher-order Kerr effect and filamentation

As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence, nor its inversion, nor the intensity at which it is observed, appear to be flawed. Furthermore, we argue that, independently on our values, the principle of including HOKE is straightforward. Due to the different temporal and spectral dynamics, the respective efficiency of defocusing by the plasma and by the HOKE is expected to depend substantially on both incident wavelength and pulse duration. The discussion should therefore focus on defining the conditions where each filamentation regime dominates.Comment: 22 pages, 11 figures. Submitted to Laser physics as proceedings of the Laser Physics 2010 conferenc

Non linear propagation of ultrashort laser pulses in transparent media

Nous présentons différents aspects de la propagation d'impulsions laser ultra-courtes dans les milieux transparents. Tout d'abord, après avoir établi les équations de propagation à partir des équations de Maxwell, nous rappelons les principaux phénomènes physiques auxquels sont soumises les impulsions ultra-courtes et de forte puissance se propageant dans un milieu transparent. Celles-ci subissent de l'auto-focalisation causée par la réponse Kerr du milieu. Cette auto-focalisation est stoppée par la création d'un plasma produit par l'ionisation photonique des molécules du milieu. La propagation de l'onde laser génère aussi un supercontinuum par auto-modulation de phase. Enfin, on rappelle les principaux résultats concernant la filamentation simple ou multiple de l'onde provenant des inhomogénéités du faisceau et qui a lieu lorsque la puissance initiale du laser est supérieure au seuil d'auto-focalisation. Dans une deuxième partie, nous nous intéressons à l'influence de non-linéarités optiques d'ordre élevé sur la propagation de l'onde et sur la figure de filamentation créée. Dans une troisième partie, afin de contrôler la filamentation multiple, nous analysons la propagation de faisceaux particuliers: les impulsions optiques femtosecondes avec gradient fort et les vortex. Nous justifions les propriétés de robustesse de ces derniers type d'objets optiques. Enfin, nous examinons la filamentation multiple d'impulsions ultra-courtes à travers une chambre à brouillard, et dans les cellules d'éthanol dopées à la coumarine, pour différentes configurations du faisceau.We present different aspects of the propagation of ultrashort laser pulses in transparent media. First, we derive the propagation equations starting from the Maxwell equations. We remind of the main physical phenomena undergone by ultrashort and powerful laser pulses. First self-focusing occurs, owing to the Kerr response of the medium. This self-focusing is stopped by plasma generation from the laser-induced ionization of the ambient atoms. The propagation of the wave generates a supercontinuum through self-phase modulation. We recall the main results concerning the simple and multiple filamentations of an intense wave, induced by the beam inhomogeneities and which take place as soon as the beam power is above critical. In a second part, we investigate the influence of high-order nonlinearities on the propagation of the beam and especially on its filamentation pattern. To control the multifilamentation process, we investigate in a third part the propagation of beams with special designs, namely; Gradient- and vortex-shaped beams. We justify the robustness of this latter kind of optical objects. Eventually, we investigate multifilamentation patterns of femtosecond pulses in a fog tube and in cells of ethanol doped with coumarine, for different beam configurations

Propagation non-linéaire d'impulsions laser ultra-courtes dans les milieux transparents

réalisée et rédigée au Commissariat à l'Energie Atomique (CEA) Département de Physique Théorique et appliquée,Bruyères-le-Châtel.We present different aspects of the propagation of ultrashort laser pulses in transparent media. First, we derive the propagation equations starting from the Maxwell equations. We remind of the main physical phenomena undergone by ultrashort and powerful laser pulses. First self-focusing occurs, owing to the Kerr response of the medium. This self-focusing is stopped by plasma generation from the laser-induced ionization of the ambient atoms. The propagation of the wave generates a supercontinuum through self-phase modulation. We recall the main results concerning the simple and multiple filamentations of an intense wave, induced by the beam inhomogeneities and which take place as soon as the beam power is above critical. In a second part, we investigate the influence of high-order nonlinearities on the propagation of the beam and especially on its filamentation pattern. To control the multifilamentation process, we investigate in a third part the propagation of beams with special designs, namely; Gradient- and vortex-shaped beams. We justify the robustness of this latter kind of optical objects. Eventually, we investigate multifilamentation patterns of femtosecond pulses in a fog tube and in cells of ethanol doped with coumarine, for different beam configurations.Nous présentons différents aspects de la propagation d'impulsions laser ultra-courtes dans les milieux transparents. Tout d'abord, après avoir établi les équations de propagation à partir des équations de Maxwell, nous rappelons les principaux phénomènes physiques auxquels sont soumises les impulsions ultra-courtes et de forte puissance se propageant dans un milieu transparent. Celles-ci subissent de l'auto-focalisation causée par la réponse Kerr du milieu. Cette auto-focalisation est stoppée par la création d'un plasma produit par l'ionisation photonique des molécules du milieu. La propagation de l'onde laser génère aussi un supercontinuum par auto-modulation de phase. Enfin, on rappelle les principaux résultats concernant la filamentation simple ou multiple de l'onde provenant des inhomogénéités du faisceau et qui a lieu lorsque la puissance initiale du laser est supérieure au seuil d'auto-focalisation. Dans une deuxième partie, nous nous intéressons à l'influence de non-linéarités optiques d'ordre élevé sur la propagation de l'onde et sur la figure de filamentation créée. Dans une troisième partie, afin de contrôler la filamentation multiple, nous analysons la propagation de faisceaux particuliers: les impulsions optiques femtosecondes avec gradient fort et les vortex. Nous justifions les propriétés de robustesse de ces derniers type d'objets optiques. Enfin, nous examinons la filamentation multiple d'impulsions ultra-courtes à travers une chambre à brouillard, et dans les cellules d'éthanol dopées à la coumarine, pour différentes configurations du faisceau

1.1. Chrono-typologie de la céramique d'Angers et réseaux d'approvisionnement de la ville

Moréra-Vinçotte Isabelle. 1.1. Chrono-typologie de la céramique d'Angers et réseaux d'approvisionnement de la ville. In: La céramique médiévale et moderne du Centre-Ouest de la France (11e - 17e siècle). Chrono-typologie de la céramique et approvisionnement de la vallée de la Loire moyenne. Tours : Fédération pour l'édition de la Revue archéologique du Centre de la France, 2003. pp. 15-22. (Supplément à la Revue archéologique du centre de la France, 20

1.1. Chrono-typologie de la céramique d'Angers et réseaux d'approvisionnement de la ville

Moréra-Vinçotte Isabelle. 1.1. Chrono-typologie de la céramique d'Angers et réseaux d'approvisionnement de la ville. In: La céramique médiévale et moderne du Centre-Ouest de la France (11e - 17e siècle). Chrono-typologie de la céramique et approvisionnement de la vallée de la Loire moyenne. Tours : Fédération pour l'édition de la Revue archéologique du Centre de la France, 2003. pp. 15-22. (Supplément à la Revue archéologique du centre de la France, 20

A 1 kHz resolution frequency study of a variety of sonochemical processes

A variety of reactions, which are known to be enhanced or driven by sonochemical effects, have been studied and their absolute rate measured as a function of the ultrasonic frequency employed within a cylindrical reactor. The rate is shown to be highly dependent on the ultrasonic frequency employed in the range of 20 kHz to 160 kHz. The frequency dependence of the system is the net result of the frequency dependencies of the transducer, the reverberant sound field, the cavitation dynamics and the chemistry. Rate variation of the reactions studied is correlated to light emission (sonoluminescence) as a function of the acoustic driving frequency with a resolution down to 1 kHz. The results are discussed with reference to the acoustic characteristics (particularly the modal nature) of the cell employed. The results are compared to the spatial peak acoustic pressure amplitude within the cell and broadband audio emission. Chemical activity could be predicted by sonoluminescence activity, which correlated with the more spatially complex sound field produced at higher frequencies. The most important finding is that characterisation of the sound field is vital in sonochemical experiments: a <3% change in the driving frequency was found to change the chemical activity by 3 orders of magnitude, because of the tuning effect of the modal sound field