Temporal broadening of attosecond photoelectron wavepackets from solid surfaces

W. A. Okell, T. Witting, D. Fabris, C. A. Arrell, J. Hengster, S. Ibrahimkutty, A. Seiler, M. Barthelmess, S. Stankov, Dangyuan Lei, Y. Sonnefraud, M. Rahmani, T. Uphues, S. A. Maier, J. P. Marangos, J. W.G. Tisch