1,721,134 research outputs found
SHEEBA: A spatial high energy electron beam analyzer
No full textElectron bunches with large energy and angle spread are not easy to be analyzed with conventional spectrometers. In this article, a device for the detection of high energy electrons is presented. This detector, based on the traces left by electrons on a stack of dosimetric films, together with an original numerical algorithm for traces deconvolution, is able to characterize both angularly and spectrally (up to some mega-electron-volts) a broad-spectrum electron bunch. A numerical test was successfully performed with a virtual electron beam, which was in turn reconstructed using a Montecarlo code (based on the CERN library GEANT4). Due to its simplicity and small size, the spatial high energy electron beam analyzer (SHEEBA) detector is particularly suitable to be used in laser plasma acceleration experiments. © 2005 American Institute of Physics
Relativistic interaction of rippled laser beams with plasmas
No full textAn investigation of the growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in a plasma is presented. Based on WKB and paraxial ray approximation the phenomenon of relativistic self-focusing (RSF) is analytically investigated. The differential equation for beamwidth parameter of rippled laser beam is evaluated. The ripple gets focused when the initial power of the ripple is greater than the critical power for focusing. The focusing is found to be considerably affected by the power of the main beam and the phase angle between the electric vectors of the main beam and the ripple. At higher intensities the saturation effects of nonlinearity become predominant, making the nonlinear refractive index in the paraxial region have slower radial dependence, and thus the ripple extract relatively less energy from its neighborhood. The case of magnetized plasmas is also preliminarily discussed
Nonlinear propagation of intense short pulses through underdense plasmas
No full textCurrently there is much interest in the interaction of high-intensity ultra-short laser pulses with plasmas. Applications include the recently proposed Fast Ignitor Concept for Inertial Confinement Fusion. In the present work we make an analytical investigation of nonlinear propagation of intense short pulses through underdense plasmas. When a laser beam is focused into a plasma, self-focusing and self-channeling can occur as a result of relativistic modification of electron mass in the laser field and the reduction of electron density on the focal region due to the expulsion of electrons by laser ponderomotive force. The paper presents a paraxial theory of self-focusing of intense laser pulses due to expulsion of plasma electrons produced by the extreme ponderomotive force of a focused laser pulse. The nonlinear dielectric constant, self-focusing equation relating the variation of beamwidth parameter with distance of propagation, self-trapping condition and critical power are evaluated. The results suggest a self-focusing of the laser pulse in the plasma
Experimental study of X-ray generation in laser-produced plasmas based on K-shell time-resolved spectroscopy
No full textSoft-X-ray generation in aluminium plasmas produced by Nd nanosecond laser pulses is investigated analysing time-resolved spectra of K-shell line emission. Time histories of line emission and electron temperature as well as the time-integrated X-ray yield were studied as a function of laser pulse duration and target position along the laser beam propagation ads. The experimental results suggest that X-ray emission is influenced by self-focusing of laser light in the plasma
Thomson backscattering X-rays from ultra-relativistic electron bunches and temporally shaped laser pulses
No full textThe process of Thomson scattering of an ultra-intense laser pulse by a relativistic electron bunch has been proposed as a way to obtain a bright source of short, tunable and quasi-monochromatic X-ray pulses. The real applicability of such a method depends crucially on the electron-beam quality, the angular and energetic distributions playing a relevant role. In this paper we present the computation of the Thomson-scattered radiation generated by a plane-wave, linearly polarized and flat-top laser pulse, incident on a counterpropagating electron bunch having a sizable angular divergence and a generic energy distribution. Both linear and nonlinear Thomson-scattering regimes are considered and the impact of the rising front of the pulse on the scattered-radiation distribution has been taken into account. Simplified relations valid for long laser pulses and small values of both scattering angle and bunch divergence are also reported. Finally, we apply the results to the cases of backscattering with electron bunches typically produced with both standard radio-frequency-based accelerators and laser-plasma accelerators
High brightness laser-plasma X-ray source at IFAM: Characterization and applications
No full textA high brightness laser-plasma X-ray source has been set-up and is presently available at IFAM. A wide range of diagnostics has been set up to monitor the properties of the X-ray radiation and to control the main parameters including photon energy, flux intensity, and pulse duration. A beam extractor enables access to the X-ray radiation at atmospheric pressure. A simple, easy-to-use projection microscope has been built which is capable of single-shot micron resolution imaging with digital acquisition. Preliminary biomedical experiments show that the X-ray doses available on a single laser shot exposure of our source fully meet the conditions required for an important class of biological experiments based on X-ray induced DNA damage providing an ideal alternative to the long time exposures needed with X-ray tubes
High-order harmonic generation from a linear chain of ions
No full textThe high-order harmonic generation process due to the interaction of a multi-well quantum system with an intense laser field is examined. A plateau extension up to a photon energy of I-p + 8U(p) and the generation of attosecond pulses are demonstrated
Magnetically induced optical transparency of overdense plasmas due to ultrafast ionization
No full textLaser light can propagate through an overdense magnetized plasma a's an extraordinary mode. The required stationary magnetic field may be supplied by ultrafast ionization of the medium [Phys. Rev. Lett. 61, 337 (1988)]. The implications of this process on the interpretation of recent unexpected results [Phys. Rev. Lett: 79, 3194 (1997)] in terms of extraordinary mode propagation, is briefly discussed. This physical mechanism opens new and exciting perspectives in high-intensity femtosecond :interaction studies and related applications
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