Abstract
Pump–probe experiments with subfemtosecond resolution are the key to understanding electronic dynamics in quantum systems. Here we demonstrate the generation and control of subfemtosecond pulse pairs from a two-colour X-ray free-electron laser. By measuring the delay between the two pulses with an angular streaking diagnostic, we characterize the group velocity of the X-ray free-electron laser and show control of the pulse delay down to 270 as. We confirm the application of this technique to a pump–probe measurement in core-ionized para-aminophenol. These results reveal the ability to perform pump–probe experiments with subfemtosecond resolution and atomic site specificity.
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Data availability
A subset of the raw data used to produce Figs. 1–4 is publicly available via Figshare at https://doi.org/10.6084/m9.figshare.23232350.v2 (ref. 61). This repository also contains a copy of the analysis script used to generate the streaking correlation maps and the photoemission spectroscopy data. All other data that support the plots within this paper and other findings of this study are available from the corresponding authors upon reasonable request.
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Acknowledgements
Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences under contract number DE-AC02-76SF00515. A.M., D.C., P.L.F., R.R.R., Z.H. and Z.G. acknowledge support from the Accelerator and Detector Research Program of the Department of Energy, Basic Energy Sciences division. Z.G., P.L.F. and R.R.R. also acknowledge support from the Robert Siemann Fellowship of Stanford University. The effort from T.D., J.W., E.I., J.T.O., A.L.W., M.F.K., P.H.B., T.J.A.W. and J.P.C. is supported by the US Department of Energy, Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences (CSGB). C.B. acknowledges funding from the Swiss National Science Foundation (SNSF) project grant 200021-197372. L.F.D., D.T. and G.A.M. acknowledge support from the US Department of Energy, Office of Science, Basic Energy Sciences under awards DE-FG02-04ER15614 and DE-SC0012462. V.A. and M.R. acknowledge support from the UK’s Engineering and Physical Sciences Research Council (EPSRC) through the grant ‘Quantum entanglement in attosecond ionization’, grant number EP/V009192/1. O.A. and J.P.M. were supported by UK EPSRC grant numbers EP/R019509/1, EP/X026094/1 and EP/T006943/1. T.W., D.S.S. and O.G. are supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under the contract number DE-AC02-05CH11231. L.Y. and G.D. were supported by the US Department of Energy, Office of Science, Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under award DE-AC02-06CH11357. D.R., A.R. and E.W. are supported by the same funding agency under grant number DE-FG02-86ER13491. S.B. and N.B. are supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences under the contract number DE-SC0012376. A.M. would like to acknowledge L. Giannessi and P. Musumeci for useful discussions and suggestions. L.I. would like to acknowledge helpful discussion with S.-K. Son and acknowledges support from DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, and the Cluster of Excellence ‘CUI: Advanced Imaging of Matter’ of the Deutsche Forschungsgemeinschaft (DFG) – EXC 2056 – project ID 390715994.
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Z.G., T.D., J.P.C. and A.M. conceived the two-colour streaking experiment. C.B., V.A., M.R., L.F.D., G.D., O.G., D.R., A.R., D.S.S., K.U., T.W., L.Y., P.H.B., J.P.M., M.F.K., P.W., N.B., T.D., J.P.C. and A.M. conceived the aminophenol pump–probe experiment. Z.G., D.C., D.B., K.A.L., J.D., P.L.F., R.R.R., N.S.S., Z.Z. and A.M. set up the attosecond XFEL configuration. Z.G., P.L.F., S.L., T.D., J.W., E.I., K.A.L., J.M.G., X.C., X.L., M.-F.L., A.K., R.O., N.S.S., E.T., M.F.K., J.P.C. and A.M. conducted the angular streaking measurements to determine the pulse separation. Z.G., T.D., S.B., D.C., J.D., P.L.F., O.A., C.B., X.C., L.F.D., G.D., R.F., O.G., J.M.G., E.I., A.K., K.A.L., S.L., X.L., M.-F.L., G.A.M., R.O., J.T.O., R.R.R., D.R., A.R., D.S.S., N.S.S., D.T., E.T., K.U., E.W., A.L.W., J.W., T.W., T.J.A.W., L.Y., Z.Z., P.H.B., J.P.M., M.F.K., P.W., N.B., J.P.C. and A.M. conducted the aminophenol pump–probe experiment. Z.G., S.B., P.L.F., S.L., T.D., Z.H., R.R.R., E.I., J.W., L.I., N.B., J.P.C. and A.M. performed the data analysis and interpreted the data. Z.G., Z.Z., R.R.R. and D.C. conducted numerical simulations of the FEL. All authors were involved in the writing of the paper.
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Extended data
Extended Data Fig. 1 Undulator configuration in the ω/2ω mode.
Values of undulator K were set to be on resonance with ω and 2ω pulses in the first and second undulator section, respectively. The transparent grey area shows the location of the magnetic delay chicane.
Extended Data Fig. 2 Measured two-dimensional projection of the photoelectron momentum distribution recorded by the c-VMI in the absence of the circularly polarised streaking field.
The left panel shows the data from Fig. 1c in polar coordinates. The 1-D trace on the right-hand-side shows the electron yield integrated over all detector angles. Two pairs of dashed lines label lower and upper bounds of integrating electron yields in 2 photoemission features for the delay analysis.
Extended Data Fig. 3 Partial covariance between the measured photon energy spectrum and the photoelectron kinetic energy spectrum in the vicinity of the carbon K-shell ionisation features.
The partial covariance uses the pump pulse intensity as a fluctuating parameter. The red curve shows the averaged photon spectra for each delay. The blue dashed line shows the best fit line to the dispersive photoemission feature. The black dotted line is the fit of the first delay that is used as a reference.
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Supplementary Figs. 1–24, Discussion and Tables 1–4.
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Guo, Z., Driver, T., Beauvarlet, S. et al. Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser. Nat. Photon. (2024). https://doi.org/10.1038/s41566-024-01419-w
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DOI: https://doi.org/10.1038/s41566-024-01419-w