Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions

Bellei, C. and Nagel, S. R. and Kar, S. and Henig, A. and Kneip, S. and Palmer, C. and Saevert, A. and Willingale, L. and Carroll, D. and Dromey, B. and Green, J. S. and Markey, K. and Simpson, P. and Clarke, R. J. and Lowe, H. and Neely, D. and Spindloe, C. and Tolley, M. and Kaluza, M. C. and Mangles, S. P. D. and McKenna, P. and Norreys, P. A. and Schreiber, J. and Zepf, M. and Davies, J. R. and Krushelnick, K. and Najmudin, Z. (2010) Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions. New Journal of Physics, 12. ISSN 1367-2630

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    Abstract

    The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of mu m-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given.