Mid-infrared electric field sampling approaching single-photon sensitivityC. Hofer, D. Gerz, M. Högner, T. P. Butler, C. Gaida, T. Heuermann, M. Gebhardt, N. Karpowicz, J. Limpert, F. Krausz and I. PupezaEPJ Web Conf., 243 (2020) 16001DOI: https://doi.org/10.1051/epjconf/202024316001