Probing the longitudinal momentum spread of the electron wave packet at the tunnel exit Claudio Cirelli, Adrian N. Pfeiffer, Alexandra S. Landsman, Mathias Smolarski, Darko Dimitrovski, Lars B. Madsen and Ursula Keller EPJ Web of Conferences, 41 (2013) 02017 Published online: 13 March 2013 DOI: 10.1051/epjconf/20134102017