Hartmann, N.N.HartmannHartmann, G.G.HartmannHeider, R.R.HeiderWagner, M. S.M. S.WagnerIlchen, M.M.IlchenBuck, J.J.BuckLindahl, A. O.A. O.LindahlBenko, C.C.BenkoGrünert, J.J.GrünertKrzywinski, J.J.KrzywinskiLiu, J.J.LiuLutman, A. A.A. A.LutmanMarinelli, A.A.MarinelliMaxwell, T.T.MaxwellMiahnahri, A. A.A. A.MiahnahriMoeller, S. P.S. P.MoellerPlanas, M.M.PlanasRobinson, J.J.RobinsonKazansky, A. K.A. K.KazanskyKabachnik, N. M.N. M.KabachnikViefhaus, J.J.ViefhausFeurer, ThomasThomasFeurerKienberger, R.R.KienbergerCoffee, R. N.R. N.CoffeeHelml, W.W.Helml2024-10-072024-10-072018https://boris-portal.unibe.ch/handle/20.500.12422/59816The time–energy information of ultrashort X-ray free-electron laser pulses generated by the Linac Coherent Light Source is measured with attosecond resolution via angular streaking of neon 1s photoelectrons. The X-ray pulses promote electrons from the neon core level into an ionization continuum, where they are dressed with the electric field of a circularly polarized infrared laser. This induces characteristic modulations of the resulting photoelectron energy and angular distribution. From these modulations we recover the single-shot attosecond intensity structure and chirp of arbitrary X-ray pulses based on self-amplified spontaneous emission, which have eluded direct measurement so far. We characterize individual attosecond pulses, including their instantaneous frequency, and identify double pulses with well-defined delays and spectral properties, thus paving the way for X-ray pump/X-ray probe attosecond free-electron laser science.en600 - Technology::620 - Engineeringarticle10.7892/boris.12007610.1038/s41566-018-0107-6