RESUMEN
The physics of the interaction of high-intensity laser pulses with underdense plasma depends not only on the interaction intensity but also on the laser pulse length. We show experimentally that as intensities are increased beyond 10(20) W cm(-2) the peak electron acceleration increases beyond that which can be produced from single stage plasma wave acceleration and it is likely that direct laser acceleration mechanisms begin to play an important role. If, alternatively, the pulse length is reduced such that it approaches the plasma period of a relativistic electron plasma wave, high-power interactions at much lower intensity enable the generation of quasi-mono-energetic beams of relativistic electrons.
RESUMEN
Experimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield.
RESUMEN
Ion acceleration by the interaction of an ultraintense short-pulse laser with an underdense-plasma has been studied at intensities up to 3 x 10(20) W/cm(2). Helium ions having a maximum energy of 13.2+/-1.0 MeV were measured at an angle of 100 degrees from the laser propagation direction. The maximum ion energy scaled with plasma density as n(0.70+/-0.05)(e). Two-dimensional particle-in-cell simulations suggest that multiple collisionless shocks are formed at high density. The interaction of shocks is responsible for the observed plateau structure in the ion spectrum and leads to an enhanced ion acceleration beyond that possible by the ponderomotive potential of the laser alone.
RESUMEN
The transverse emittance of a relativistic electron beam generated by the interaction of a high-intensity laser with an underdense plasma has been measured with the "pepper-pot" method. For parameters pertaining to the forced laser wakefield regime, we have measured an emittance as low as (2.7+/-0.9) pi mm mrad for (55+/-2) MeV electrons. These measurements are consistent with 3D particle-in-cell simulations of the experiment, which additionally show the existence of a relatively large halo around the beam core.
RESUMEN
We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a(0). This radiative process is dominant for a(0) greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.
RESUMEN
Plasmas are an attractive medium for the next generation of particle accelerators because they can support electric fields greater than several hundred gigavolts per meter. These accelerating fields are generated by relativistic plasma waves-space-charge oscillations-that can be excited when a high-intensity laser propagates through a plasma. Large currents of background electrons can then be trapped and subsequently accelerated by these relativistic waves. In the forced laser wake field regime, where the laser pulse length is of the order of the plasma wavelength, we show that a gain in maximum electron energy of up to 200 megaelectronvolts can be achieved, along with an improvement in the quality of the ultrashort electron beam.
RESUMEN
Thermonuclear fusion neutrons produced by D(d,n)3He reactions have been measured from the interaction of a high-intensity laser with underdense deuterium plasmas. For an input laser energy of 62 J, more than (1.0+/-0.2)x10(6) neutrons with a mean kinetic energy of (2.5+/-0.2) MeV were detected. These neutrons were observed to have an isotropic angular emission profile. By comparing these measurements with those using a secondary solid CD2 target it was determined that neutrons are produced from direct ion heating during this interaction.
RESUMEN
A short-pulse laser beat wave scheme for advanced particle accelerator applications is examined. A short, intense (3-ps, >10(18)-W cm(-2)) two-frequency laser pulse is produced by use of a modified chirped-pulse amplification scheme and is shown to produce relativistic plasma waves during interactions with low-density plasmas. The generation of plasma waves was observed by measurement of forward Raman scattering. Resonance was found to occur at an electron density many times that expected, owing to ponderomotive displacement of plasma within the focal region.
RESUMEN
Energy and angular distributions of the fast outgoing electron beam induced by the interaction of a 1 J, 30 fs, 2 x 10(19) W/cm(2), 10 Hz laser with a thin foil target are characterized by electron energy spectroscopy and photonuclear reactions. We have investigated the effect of the target thickness and the intensity contrast ratio level on the electron production. Using a 6-microm polyethylene target, up to 4 x 10(8) electrons with energies between 5 and 60 MeV were produced per laser pulse and converted to gamma rays by bremsstrahlung in a Ta secondary target. The rates of photofission of U as well as photonuclear reactions in Cu, Au, and C samples have been measured. In optimal focusing conditions, about 0.06% of the laser energy has been converted to outgoing electrons with energies above 5 MeV. Such electrons leave the target in the laser direction with an opening angle of 2.5 degrees.
