Results 1 - 10 of 16535
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[en] Spatial beam shaping is an important topic for the lasers applications. For various industrial areas (marking, drilling, laser-matter interaction, high-power laser seeding...) the optical beam has to be flattened. Currently, the state of the art of the beam shaping: 'free-space' solutions or highly multimode fibers, are not fully suitable. The first ones are very sensitive to any perturbations and the maintenance is challenging, the second ones cannot deliver a coherent beam. For this reason, we present in this manuscript a micro-structured optical single-mode fiber delivering a spatially flattened beam. This 'Top-Hat' fiber can shape any beam in a spatially coherent beam what is a progress with respect to the highly multimode fibers used in the state of the art. The optical fibers are easy to use and very robust, what is a strong benefit with respect to the 'free-space' solutions. Thanks to this fiber, we could realize an all-fiber multi-stage laser chain to amplify a 10 ns pulse to 100 μJ. Moreover the temporal, spectral and spatial properties were preserved. We adapted this 'Top-Hat' fiber to this multi-stage laser chain, we proved the capability and the interest of this fiber for the spatial beam shaping of the laser beams in highly performing and robust laser systems. (author)
[fr]La mise en forme spatiale est une problematique importante pour les lasers et ses applications. Dans de nombreux domaines (l'industrie, l'interaction laser-matiere, l'injection des lasers de puissance...) il est indispensable que le faisceau laser ait une forme aplatie. Les solutions actuelles de mise en forme spatiale d'un faisceau laser quelconque en faisceau aplati (par les techniques 'espace-libre' ou par les fibres fortement multimodes) ne sont pas satisfaisantes. Elles occasionnent des difficultes de maintenance, sont tres sensibles aux perturbations du systeme et elles ne permettent pas de delivrer un faisceau spatialement coherent. Pour cette raison nous presentons dans ce manuscrit une fibre optique microstructuree monomode delivrant un faisceau spatialement aplati. Cette fibre 'mode-plat' permet de transformer n'importe quel faisceau en un faisceau aplati coherent spatialement ce qui est un progres par rapport aux fibres fortement multimodes utilisees jusque-la. L'interet des fibres optiques est egalement leur maintenance facilitee et leur robustesse, cette solution est donc d'un grand avantage par rapport aux solutions 'espace-libres'. Grace a cette fibre, nous avons pu realiser une chaine laser entierement fibree permettant d'amplifier une impulsion d'une duree de 10 ns jusqu'a 100 μJ tout en controlant ses proprietes temporelles, spectrales et spatiales. En adaptant la fibre 'mode-plat' a cette chaine laser, nous avons demontre la faisabilite et l'interet de cette fibre pour la mise en forme spatiale de faisceaux laser dans des systemes performants et robustes
[en] Utilizing the significant shape recovery ability (in the order of 100% strain) in shape memory polymers (SMPs), we propose two simple approaches, namely laser heating and indentation, to produce micro-sized protrusion arrays. In the former, after local laser heating a pre-compressed SMP, protrusive bumps can be produced. In the latter, through an indentation-polishing-heating process, various shaped protrusive bumps can be produced. It is to demonstrate that indentation is a more convenient and powerful approach than laser heating, since well controlled, different shaped protrusion arrays can be realized. (note)
[en] A new controllable laser beam shaping technique is demonstrated, where a magnetic fluid-based liquid deformable mirror is proposed to redistribute the laser phase profile and thus change the propagation property of the beam. The mirror is driven by an inner miniature actuator array along with a large outer actuator. The inner actuator array is used for deforming the magnetic fluid surface, while the outer actuator is used to linearize the fluid surface response and amplify the magnitude of the deflection. In comparison to other laser beam shaping techniques, this technique offers the advantages such as simplicity, low cost, large shape deformation, and high adaptability. Based on a fabricated prototype of the liquid deformable mirror, an experimental AO system was set up to produce a desired conical surface shape that shaped the incident beam into a Bessel beam. The experimental results show the effectiveness of the proposed technique for laser beam shaping. (paper)
[en] Analytical theories of the geodesic acoustic mode (GAM) are reviewed in the small-and large-orbit drift width limits, respectively. Different physics pictures in these two limits are displayed. As an example, these two analytical methods are employed to investigate the plasma shaping effect on the frequency and collisionless damping rate of the GAM.
[en] We present a random effects spline regression model based on splines that provides an integrated approach for analyzing functional data, i.e., curves, when the shape of the curves is not parametrically specified. An analysis using this model is presented that makes inferences about a population of curves as well as features of the curves.
[en] In the year 2000, a design concept of a Neutrino Factory based on Muon Storage Ring was studied at FNAL. To treat high energy spread of muons that come out of a target and decay channel and are to be accelerated before they go into the storage ring, a phase rotating scheme using a long-pulse accelerating system has been proposed. In this system accelerating voltage is to be shaped to correct the energy spread. To implement this approach, the pulse power system has been suggested that allows forming a bipolar accelerating voltage pulse with the predefined shape. This report addresses some issues of the pulse shape optimization and describes main features of the accelerating system comprising an accelerating structure similar to that of a linear induction accelerator (LIA) and a pulser that drives it