Snapshots of laser wakefields Matlis, N. H; Downer, M. C; Reed, S ...
Nature physics,
11/2006, Volume:
2, Issue:
11
Journal Article
Peer reviewed
Open access
Tabletop plasma accelerators can now produce GeV-range electron beams and femtosecond X-ray pulses, providing compact radiation sources for medicine, nuclear engineering, materials science and ...high-energy physics. In these accelerators, electrons surf on electric fields exceeding 100 GeV m−1, which is more than 1,000 times stronger than achievable in conventional accelerators. These fields are generated within plasma structures (such as Langmuir waves or electron density 'bubbles') propagating near light speed behind laser or charged-particle driving pulses. Here, we demonstrate single-shot visualization of laser-wakefield accelerator structures for the first time. Our 'snapshots' capture the evolution of multiple wake periods, detect structure variations as laser-plasma parameters change, and resolve wavefront curvature; features never previously observed.
In connection with the rapid development of information technology, modern society is in need of solving the problems of the accumulation, storage and automated processing of semiotically ...heterogeneous arrays of texts. An important task of the developed technologies is the search for operational methods for issuing a wide variety of information in accordance with the user’s request. The aim of the proposed work is to develop a computer information system that allows you to select the most appropriate illustration for the given text of the advertisement. In this case, the main content of the text is proposed to be presented in the form of a certain set of main and secondary keywords, and the content of the illustration in the form of a multi-level complex of descriptors. The proximity of these contents (and, accordingly, the correlation between the image and the verbal component of the advertisement) can be determined through the maximum number of matches of support words and descriptors, taking into account their importance. An important feature of this system is the use of a thesaurus method of representing the image content, which is a description of the illustration in the form of a certain set of words and the relations between these words within a certain subject area.
We study propagation of a relativistic electron bunch through a cold plasma assuming that the transverse and longitudinal dimensions of the bunch are much smaller than the plasma collisionless skin ...depth. Treating the bunch as a point charge and assuming that its charge is small, we derive a simplified system of equations for the plasma electrons and show that, through a simple rescaling of variables, the bunch charge can be eliminated from the equations. The equations demonstrate an ion cavity formed behind the driver. They are solved numerically and the scaling of the cavity parameters with the driver charge is obtained. A numerical solution for the case of a positively charged driver is also found.
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We demonstrate that plasmonic response can be tuned spectrally via the alloy composition of an epitaxial semimetallic film. Specifically, attenuated total reflectance studies show that the surface ...plasmon resonance of rare-earth monopnictide La x Lu1–x As alloy films can be tuned across the mid-IR, while lattice-matching to technologically important substrates. The electrical properties are a strong function of the composition, which, in turn, manifests as tunability of the optical properties. The ability to produce tunable (semi)metals that can be epitaxially integrated with III–V emitters and absorbers is expected to enable a new generation of novel nanophotonic device architectures and functionality.
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