Characterization of spectral entanglement of spontaneous parametric-down conversion biphotons in femtosecond pulsed regimeG. Brida, V. Caricato, M. V. Fedorov, M. Genovese, M. Gramegna and S. P. KulikEPL, 87 6 (2009) 64003DOI: https://doi.org/10.1209/0295-5075/87/64003