Relativistic high harmonics and (sub-)attosecond pulses: relativistic spikes and relativistic mirrorA. Pukhov, T. Baeva, D. an der Brügge and S. MünsterEur. Phys. J. D, 55 2 (2009) 407-414DOI: https://doi.org/10.1140/epjd/e2009-00187-4