Showing papers by "David Neely published in 2006"

Enhanced proton beams from ultrathin targets driven by high contrast laser pulses

Abstract: The generation of proton beams from ultrathin targets, down to 20 nm in thickness, driven with ultrahigh contrast laser pulses is explored. the conversion efficiency from laser energy into protons increases as the foil thickness is decreased, with good beam quality and high efficiencies of 1% being achieved, for protons with kinetic energy exceeding 0.9 MeV, for 100 nm thick aluminum foils at intensities of 10(19) W/cm(2) with 33 fs, 0.3 J pulses. To minimize amplified spontaneous emission (ASE) induced effects disrupting the acceleration mechanism, exceptional laser to ASE intensity contrasts of up to 1010 are achieved by introducing a plasma mirror to the high contrast 10 Hz multiterawatt laser at the Lund Laser Centre. It is shown that for a given laser energy on target, regimes of higher laser-to-proton energy conversion efficiency. can be accessed with increasing contrast. The increasing efficiency as the target thickness decreases is closely correlated to an increasing proton temperature. (c) 2006 American Institute of Physics.

Laser-driven shock experiments on precompressed water: Implications for “icy” giant planets

Abstract: Laser-driven shock compression of samples precompressed to 1GPa produces high-pressure-temperature conditions inducing two significant changes in the optical properties of water: the onset of opacity followed by enhanced reflectivity in the initially transparent water. The onset of reflectivity at infrared wavelengths can be interpreted as a semiconductor↔electronic conductor transition in water, and is found at pressures above ∼130GPa for single-shocked samples precompressed to 1GPa. Our results indicate that conductivity in the deep interior of “icy” giant planets is greater than realized previously because of an additional contribution from electrons.

High-intensity laser-driven proton acceleration : influence of pulse contrast

Abstract: Proton acceleration from the interaction of ultra-short laser pulses with thin foil targets at intensities greater than 10 18 Wc m K2 is discussed. An overview of the physical processes giving rise to the generation of protons with multi-MeV energies, in well defined beams with excellent spatial quality, is presented. Specifically, the discussion centres on the influence of laser pulse contrast on the spatial and energy distributions of accelerated proton beams. Results from an ongoing experimental investigation of proton acceleration using the 10 Hz multi-terawatt Ti : sapphire laser (35 fs, 35 TW) at the Lund Laser Centre are discussed. It is demonstrated that a window of amplified spontaneous emission (ASE) conditions exist, for which the direction of proton emission is sensitive to the ASE-pedestal preceding the peak of the laser pulse, and that by significantly improving the temporal contrast, using plasma mirrors, efficient proton acceleration is observed from target foils with thickness less than 50 nm.

Vulcan petawatt-operation and development

Abstract: Petawatt capability on the Vulcan laser facility has been available to the international plasma physics community for over two years. This has enabled novel experiments to be carried out and new regimes of physics to be explored. During that time, there have been 10 successful user experiments with 89% of shots delivered within the requested energy limits. In the autumn of 2004, pulses with powers of more than a petawatt (10 15 Watts) were delivered to target with energies greater than 400 J and pulse widths shorter than 500 femtoseconds (10 -15 ) on target. In parallel to the development of ultra-high intensity pulses is a programme to enhance Vulcan's long pulse capabilities. This paper will present an overview of the current capabilities of the Vulcan Petawatt facility and discuss some of the recent technological advances that have enabled the generation of Petawatt pulses.

Detection of short lived radioisotopes as a fast diagnostic for intense laser-solid interactions

Abstract: As a diagnostic of high-intensity laser interactions (>1019Wcm−2), the detection of radioactive isotopes is regularly used for the characterization of proton, neutron, ion, and photon beams. This involves sample removal from the interaction chamber and time consuming post shot analysis using NaI coincidence counting or Ge detectors. This letter describes the use of in situ detectors to measure laser-driven (p,n) reactions in Al27 as an almost real-time diagnostic for proton acceleration. The produced Si27 isotope decays with a 4.16s half-life by the predominantly β+ emission, producing a strong 511keV annihilation peak.