Oxford Centre for High Energy Density Science (OxCHEDS)

Abstract:

We have studied the focusing properties of two highly oriented pyrolitic graphite (HOPG) spectrometers, which differ in the degree of the mosaic spread: ZYA with a low mosaic spread (gamma=0.4degrees) and ZYH with a large mosaic spread (gamma=3.5degrees). In order to asses the crystal performance for a variety of different experiments, various Kalpha and Kbeta x-ray lines have been produced using a high-intensity (greater than or similar to10(17) W/cm(2)) short-pulse (similar to100 fs) laser beam focused onto Ti, V, Zn, and Cu foils. The measured spectral resolution of the HOPG crystals in both first and second order diffraction has been compared with theoretical predictions. Using known values for the peak reflectivity of HOPG crystals, we have also computed Kalpha x-ray conversion efficiencies of Ti, V, Zn, and Cu. These results are important to estimate the optimal conditions under which different types of HOPG monochromators can be used for the detection of weak x-ray signals as the one encountered in x-ray Thomson/Compton scattering experiments. (C) 2004 American Institute of Physics.

Abstract:

High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 10 19 W cm -2 at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and γ-rays. Relativistic electrons are generated through the breaking of large-amplitude relativistic plasma waves created in the wake of the laser pulse as it propagates through a plasma, or through a direct interaction between the laser field and the electrons in the plasma. However, the electron beams produced from previous laser-plasma experiments have a large energy spread, limiting their use for potential applications. Here we report high-resolution energy measurements of the electron beams produced from intense laser-plasma interactions, showing that-under particular plasma conditions-it is possible to generate beams of relativistic electrons with low divergence and a small energy spread (less than three per cent). The monoenergetic features were observed in the electron energy spectrum for plasma densities just above a threshold required for breaking of the plasma wave. These features were observed consistently in the electron spectrum, although the energy of the beam was observed to vary from shot to shot. If the issue of energy reproducibility can be addressed, it should be possible to generate ultrashort monoenergetic electron bunches of tunable energy, holding great promise for the future development of 'table-top' particle accelerators.

Abstract:

The investigation of proton and heavy ion acceleration was carried out in ultrahigh intensity laser plasma interactions using VULCAN lasers. The first spatially integrated measurement of proton and heavy ion acceleration was performed with nuclear activation techniques. High-intensity laser-plasma interactions provide a unique and potentially important source of nuclear radiation for radioisotope production. By controlling the target conditions and the accelerated ion beam properties, the production of radioisotopes can be controlled effectively.