Abstract
Light–electron interaction is the seminal ingredient in free-electron lasers and dynamical investigation of matter. Pushing the coherent control of electrons by light to the attosecond timescale and below would enable unprecedented applications in quantum circuits and exploration of electronic motions and nuclear phenomena. Here we demonstrate attosecond coherent manipulation of a free-electron wave function, and show that it can be pushed down to the zeptosecond regime. We make a relativistic single-electron wavepacket interact in free-space with a semi-infinite light field generated by two light pulses reflected from a mirror and delayed by fractions of the optical cycle. The amplitude and phase of the resulting electron–state coherent oscillations are mapped in energy-momentum space via momentum-resolved ultrafast electron spectroscopy. The experimental results are in full agreement with our analytical theory, which predicts access to the zeptosecond timescale by adopting semi-infinite X-ray pulses.
Highlights
A direct single-photon emission/absorption process can bridge the energy-momentum mismatch if either the electrons are not free or when a scattering structure generates evanescent light fields[11] in the vicinity of the interaction volume
Such an electron–photon–matter interaction creates optical field components with a frequency–momentum decomposition that lies outside the light cone, allowing emission/absorption to take place. This type of interaction, which is forbidden in freespace[12,13], is regularly exploited for generating radiation and for accelerating charged particles. It has prompted the development of photon-induced near-field electron microscopy (PINEM)[11,14,15,16]
The microscopic details of the process are encoded in the electron wave function, which can be revealed via ultrafast electron energy-loss spectroscopy (EELS) and controlled using suitable illumination schemes[20,21]
Summary
A direct single-photon emission/absorption process can bridge the energy-momentum mismatch if either the electrons are not free (for example, in photoemission from atoms/molecules[9] and solid surfaces10) or when a scattering structure generates evanescent light fields[11] in the vicinity of the interaction volume. Our experimental results are successfully described within a general theoretical framework for electron–light interaction, which is able to further predict the ability of this method to achieve coherent control over the electron wave function down to the zeptosecond regime using semi-infinite X-ray fields.
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