Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions by Bellei, C, Nagel, SR, Kar, S, Henig, A, Kneip, S, Palmer, C, Sävert, A, Willingale, L, Carroll, D, Dromey, B, Green, J, Markey, K, Simpson, P, Clarke, R, Lowe, H, Neely, D, Spindloe, C, Tolley, M, Kaluza, M, Mangles, S, McKenna, P, Norreys, P, Schreiber, J, Zepf, M, Davies, JR