Time-frequency characterization of high-order harmonic pulsesR. López-Martens, J. Mauritsson, A. Johansson, J. Norin and A. L'HuillierEur. Phys. J. D, 26 1 (2003) 105-109DOI: https://doi.org/10.1140/epjd/e2003-00085-9