Abstract
In the early days of quantum mechanics Kapitza and Dirac predicted that matter waves would scatter off the optical intensity grating formed by two counter-propagating light waves1. This interaction, driven by the ponderomotive potential of the optical standing wave, was both studied theoretically and demonstrated experimentally for atoms2 and electrons3,4,5. In the original version of the experiment1,5, only the transverse momentum of particles was varied, but their energy and longitudinal momentum remained unchanged after the interaction. Here, we report on the generalization of the Kapitza–Dirac effect. We demonstrate that the energy of sub-relativistic electrons is strongly modulated on the few-femtosecond timescale via the interaction with a travelling wave created in vacuum by two colliding laser pulses at different frequencies. This effect extends the possibilities of temporal control of freely propagating particles with coherent light and can serve the attosecond ballistic bunching of electrons6, or for the acceleration of neutral atoms or molecules by light.
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Acknowledgements
We thank T. Higuchi and J. McNeur for proof-reading of the manuscript. The authors acknowledge funding from ERC grant ‘Near Field Atto’. This publication is funded in part by the Gordon and Betty Moore Foundation through Grant GBMF4744 ‘Accelerator on a Chip International Program – ACHIP’ and by BMBF via a project with contract number 05K16WEC.
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M.K. planned and carried out the experiments, processed the data and performed the simulations. T.E. designed and fabricated the electromagnetic spectrometer. N.S. developed the controlling software for data acquisition. M.K. and P.H. interpreted the results and wrote the manuscript with contributions of all authors.
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Kozák, M., Eckstein, T., Schönenberger, N. et al. Inelastic ponderomotive scattering of electrons at a high-intensity optical travelling wave in vacuum. Nat. Phys. 14, 121–125 (2018). https://doi.org/10.1038/nphys4282
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DOI: https://doi.org/10.1038/nphys4282
