Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We describe measurements characterizing the interaction of ultra-high intensity Petawatt laser pulses with solid targets. Experiments were performed on the Petawatt laser at RAL, and the Titan laser at LLNL. © 2006 Optical Society of America.

Abstract:

In situ diffraction is a technique to probe directly the lattice response of materials during the shock loading process. It is used to record diffraction patterns from multiple lattice planes simultaneously. The application of this technique is described for laser-based shock experiments. The approach to analyze in situ wide-angle diffraction data is discussed. This is presented in the context of single crystal [001] iron shock experiments where uniaxial compression of the bee lattice by up to 6% was observed. Above the alpha-epsilon transition pressure, the lattice showed a collapse along the [001] direction by 15-18%. Additional diffraction lines appear that confirm the transformation of the iron crystal from the initial bee phase to the hcp phase. (C) 2006 Elsevier Ltd. All rights reserved.

Abstract:

We derive expressions for the coupling coefficients for electromagnetic four-wave mixing in the nonlinear quantum vacuum. An experimental setup for detection of elastic photon-photon scattering is suggested, where three incoming laser pulses collide and generate a fourth wave with a new frequency and direction of propagation. An expression for the number of scattered photons is derived and, using beam parameters for the Astra Gemini system at the Rutherford Appleton Laboratory, it is found that the signal can reach detectable levels. Problems with shot-to-shot reproducibility are reviewed, and the magnitude of the noise arising from competing scattering processes is estimated. It is found that detection of elastic photon-photon scattering may be achieved. © 2006 The American Physical Society.

Abstract:

The operation of target diagnostics in a high-energy petawatt laser environment is made challenging by the large number of energetic electrons, hard x rays, and energetic particles produced in laser-target interactions. The charged particles and x rays from the target create secondary radiation and a large electromagnetic pulse (EMP) when they hit structures inside the target chamber. The primary particles create secondary particles and radiation that can create excessive background in sensitive detectors. The large EMP can impair or damage electronic equipment and detectors, especially inside the target chamber. Shielding and EMP mitigation strategies developed during experiments at the Rutherford Appleton Vulcan petawatt laser facility will be presented for a variety of detection systems, such as single-photon-counting x-ray charge-coupled device cameras, multiple diamond x-ray detectors, and scintillator-photomultiplier detectors. These strategies will be applied to the development of diagnostic systems for the OMEGA EP, high-energy petawatt laser facility, currently under construction at the Laboratory for Laser Energetics. © 2006 American Institute of Physics.