Time-frequency characterization of high-order harmonic pulses R. López-Martens, J. Mauritsson, A. Johansson, J. Norin and A. L'Huillier Eur. Phys. J. D, 26 1 (2003) 105-109 Published online: 24 April 2003 DOI: 10.1140/epjd/e2003-00085-9